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different fields. We can show that two GEPs off of the same (possibly multidimensional) array of structs, into different fields, can't alias. Quoting: For two GEPOperators GEP1 and GEP2, if we find that: - both GEPs begin indexing from the exact same pointer; - the last indices in both GEPs are constants, indexing into a struct; - said indices are different, hence,the pointed-to fields are different; - and both GEPs only index through arrays prior to that; this lets us determine that the struct that GEP1 indexes into and the struct that GEP2 indexes into must either precisely overlap or be completely disjoint. Because they cannot partially overlap, indexing into different non-overlapping fields of the struct will never alias. The other BasicAA::aliasGEP rules worked in some cases, but not all (for example, the i32x3 struct in the testcase). We can add this simple ad-hoc rule to complement them. rdar://19717375 Differential Revision: http://reviews.llvm.org/D7453 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228498 91177308-0d34-0410-b5e6-96231b3b80d8
1595 lines
63 KiB
C++
1595 lines
63 KiB
C++
//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the primary stateless implementation of the
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// Alias Analysis interface that implements identities (two different
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// globals cannot alias, etc), but does no stateful analysis.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/Passes.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/AssumptionCache.h"
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#include "llvm/Analysis/CFG.h"
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#include "llvm/Analysis/CaptureTracking.h"
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#include "llvm/Analysis/InstructionSimplify.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/MemoryBuiltins.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GetElementPtrTypeIterator.h"
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#include "llvm/IR/GlobalAlias.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Operator.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/ErrorHandling.h"
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#include <algorithm>
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using namespace llvm;
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/// Cutoff after which to stop analysing a set of phi nodes potentially involved
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/// in a cycle. Because we are analysing 'through' phi nodes we need to be
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/// careful with value equivalence. We use reachability to make sure a value
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/// cannot be involved in a cycle.
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const unsigned MaxNumPhiBBsValueReachabilityCheck = 20;
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// The max limit of the search depth in DecomposeGEPExpression() and
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// GetUnderlyingObject(), both functions need to use the same search
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// depth otherwise the algorithm in aliasGEP will assert.
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static const unsigned MaxLookupSearchDepth = 6;
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//===----------------------------------------------------------------------===//
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// Useful predicates
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//===----------------------------------------------------------------------===//
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/// isNonEscapingLocalObject - Return true if the pointer is to a function-local
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/// object that never escapes from the function.
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static bool isNonEscapingLocalObject(const Value *V) {
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// If this is a local allocation, check to see if it escapes.
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if (isa<AllocaInst>(V) || isNoAliasCall(V))
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// Set StoreCaptures to True so that we can assume in our callers that the
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// pointer is not the result of a load instruction. Currently
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// PointerMayBeCaptured doesn't have any special analysis for the
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// StoreCaptures=false case; if it did, our callers could be refined to be
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// more precise.
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return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
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// If this is an argument that corresponds to a byval or noalias argument,
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// then it has not escaped before entering the function. Check if it escapes
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// inside the function.
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if (const Argument *A = dyn_cast<Argument>(V))
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if (A->hasByValAttr() || A->hasNoAliasAttr())
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// Note even if the argument is marked nocapture we still need to check
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// for copies made inside the function. The nocapture attribute only
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// specifies that there are no copies made that outlive the function.
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return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
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return false;
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}
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/// isEscapeSource - Return true if the pointer is one which would have
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/// been considered an escape by isNonEscapingLocalObject.
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static bool isEscapeSource(const Value *V) {
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if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V))
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return true;
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// The load case works because isNonEscapingLocalObject considers all
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// stores to be escapes (it passes true for the StoreCaptures argument
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// to PointerMayBeCaptured).
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if (isa<LoadInst>(V))
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return true;
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return false;
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}
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/// getObjectSize - Return the size of the object specified by V, or
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/// UnknownSize if unknown.
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static uint64_t getObjectSize(const Value *V, const DataLayout &DL,
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const TargetLibraryInfo &TLI,
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bool RoundToAlign = false) {
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uint64_t Size;
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if (getObjectSize(V, Size, &DL, &TLI, RoundToAlign))
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return Size;
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return AliasAnalysis::UnknownSize;
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}
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/// isObjectSmallerThan - Return true if we can prove that the object specified
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/// by V is smaller than Size.
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static bool isObjectSmallerThan(const Value *V, uint64_t Size,
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const DataLayout &DL,
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const TargetLibraryInfo &TLI) {
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// Note that the meanings of the "object" are slightly different in the
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// following contexts:
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// c1: llvm::getObjectSize()
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// c2: llvm.objectsize() intrinsic
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// c3: isObjectSmallerThan()
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// c1 and c2 share the same meaning; however, the meaning of "object" in c3
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// refers to the "entire object".
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//
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// Consider this example:
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// char *p = (char*)malloc(100)
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// char *q = p+80;
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//
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// In the context of c1 and c2, the "object" pointed by q refers to the
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// stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
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//
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// However, in the context of c3, the "object" refers to the chunk of memory
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// being allocated. So, the "object" has 100 bytes, and q points to the middle
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// the "object". In case q is passed to isObjectSmallerThan() as the 1st
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// parameter, before the llvm::getObjectSize() is called to get the size of
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// entire object, we should:
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// - either rewind the pointer q to the base-address of the object in
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// question (in this case rewind to p), or
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// - just give up. It is up to caller to make sure the pointer is pointing
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// to the base address the object.
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//
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// We go for 2nd option for simplicity.
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if (!isIdentifiedObject(V))
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return false;
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// This function needs to use the aligned object size because we allow
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// reads a bit past the end given sufficient alignment.
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uint64_t ObjectSize = getObjectSize(V, DL, TLI, /*RoundToAlign*/true);
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return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size;
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}
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/// isObjectSize - Return true if we can prove that the object specified
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/// by V has size Size.
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static bool isObjectSize(const Value *V, uint64_t Size,
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const DataLayout &DL, const TargetLibraryInfo &TLI) {
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uint64_t ObjectSize = getObjectSize(V, DL, TLI);
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return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size;
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}
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//===----------------------------------------------------------------------===//
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// GetElementPtr Instruction Decomposition and Analysis
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//===----------------------------------------------------------------------===//
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namespace {
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enum ExtensionKind {
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EK_NotExtended,
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EK_SignExt,
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EK_ZeroExt
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};
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struct VariableGEPIndex {
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const Value *V;
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ExtensionKind Extension;
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int64_t Scale;
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bool operator==(const VariableGEPIndex &Other) const {
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return V == Other.V && Extension == Other.Extension &&
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Scale == Other.Scale;
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}
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bool operator!=(const VariableGEPIndex &Other) const {
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return !operator==(Other);
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}
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};
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}
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/// GetLinearExpression - Analyze the specified value as a linear expression:
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/// "A*V + B", where A and B are constant integers. Return the scale and offset
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/// values as APInts and return V as a Value*, and return whether we looked
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/// through any sign or zero extends. The incoming Value is known to have
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/// IntegerType and it may already be sign or zero extended.
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///
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/// Note that this looks through extends, so the high bits may not be
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/// represented in the result.
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static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
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ExtensionKind &Extension,
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const DataLayout &DL, unsigned Depth,
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AssumptionCache *AC, DominatorTree *DT) {
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assert(V->getType()->isIntegerTy() && "Not an integer value");
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// Limit our recursion depth.
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if (Depth == 6) {
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Scale = 1;
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Offset = 0;
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return V;
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}
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if (ConstantInt *Const = dyn_cast<ConstantInt>(V)) {
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// if it's a constant, just convert it to an offset
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// and remove the variable.
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Offset += Const->getValue();
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assert(Scale == 0 && "Constant values don't have a scale");
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return V;
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}
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if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
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if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
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switch (BOp->getOpcode()) {
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default: break;
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case Instruction::Or:
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// X|C == X+C if all the bits in C are unset in X. Otherwise we can't
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// analyze it.
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if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), &DL, 0, AC,
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BOp, DT))
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break;
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// FALL THROUGH.
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case Instruction::Add:
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V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
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DL, Depth + 1, AC, DT);
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Offset += RHSC->getValue();
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return V;
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case Instruction::Mul:
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V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
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DL, Depth + 1, AC, DT);
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Offset *= RHSC->getValue();
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Scale *= RHSC->getValue();
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return V;
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case Instruction::Shl:
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V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
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DL, Depth + 1, AC, DT);
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Offset <<= RHSC->getValue().getLimitedValue();
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Scale <<= RHSC->getValue().getLimitedValue();
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return V;
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}
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}
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}
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// Since GEP indices are sign extended anyway, we don't care about the high
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// bits of a sign or zero extended value - just scales and offsets. The
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// extensions have to be consistent though.
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if ((isa<SExtInst>(V) && Extension != EK_ZeroExt) ||
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(isa<ZExtInst>(V) && Extension != EK_SignExt)) {
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Value *CastOp = cast<CastInst>(V)->getOperand(0);
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unsigned OldWidth = Scale.getBitWidth();
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unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
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Scale = Scale.trunc(SmallWidth);
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Offset = Offset.trunc(SmallWidth);
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Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt;
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Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension, DL,
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Depth + 1, AC, DT);
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Scale = Scale.zext(OldWidth);
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// We have to sign-extend even if Extension == EK_ZeroExt as we can't
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// decompose a sign extension (i.e. zext(x - 1) != zext(x) - zext(-1)).
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Offset = Offset.sext(OldWidth);
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return Result;
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}
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Scale = 1;
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Offset = 0;
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return V;
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}
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/// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it
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/// into a base pointer with a constant offset and a number of scaled symbolic
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/// offsets.
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///
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/// The scaled symbolic offsets (represented by pairs of a Value* and a scale in
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/// the VarIndices vector) are Value*'s that are known to be scaled by the
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/// specified amount, but which may have other unrepresented high bits. As such,
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/// the gep cannot necessarily be reconstructed from its decomposed form.
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///
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/// When DataLayout is around, this function is capable of analyzing everything
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/// that GetUnderlyingObject can look through. To be able to do that
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/// GetUnderlyingObject and DecomposeGEPExpression must use the same search
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/// depth (MaxLookupSearchDepth).
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/// When DataLayout not is around, it just looks through pointer casts.
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///
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static const Value *
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DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
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SmallVectorImpl<VariableGEPIndex> &VarIndices,
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bool &MaxLookupReached, const DataLayout *DL,
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AssumptionCache *AC, DominatorTree *DT) {
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// Limit recursion depth to limit compile time in crazy cases.
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unsigned MaxLookup = MaxLookupSearchDepth;
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MaxLookupReached = false;
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BaseOffs = 0;
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do {
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// See if this is a bitcast or GEP.
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const Operator *Op = dyn_cast<Operator>(V);
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if (!Op) {
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// The only non-operator case we can handle are GlobalAliases.
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if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
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if (!GA->mayBeOverridden()) {
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V = GA->getAliasee();
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continue;
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}
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}
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return V;
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}
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if (Op->getOpcode() == Instruction::BitCast ||
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Op->getOpcode() == Instruction::AddrSpaceCast) {
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V = Op->getOperand(0);
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continue;
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}
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const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
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if (!GEPOp) {
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// If it's not a GEP, hand it off to SimplifyInstruction to see if it
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// can come up with something. This matches what GetUnderlyingObject does.
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if (const Instruction *I = dyn_cast<Instruction>(V))
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// TODO: Get a DominatorTree and AssumptionCache and use them here
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// (these are both now available in this function, but this should be
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// updated when GetUnderlyingObject is updated). TLI should be
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// provided also.
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if (const Value *Simplified =
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SimplifyInstruction(const_cast<Instruction *>(I), DL)) {
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V = Simplified;
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continue;
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}
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return V;
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}
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// Don't attempt to analyze GEPs over unsized objects.
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if (!GEPOp->getOperand(0)->getType()->getPointerElementType()->isSized())
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return V;
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// If we are lacking DataLayout information, we can't compute the offets of
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// elements computed by GEPs. However, we can handle bitcast equivalent
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// GEPs.
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if (!DL) {
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if (!GEPOp->hasAllZeroIndices())
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return V;
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V = GEPOp->getOperand(0);
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continue;
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}
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unsigned AS = GEPOp->getPointerAddressSpace();
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// Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
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gep_type_iterator GTI = gep_type_begin(GEPOp);
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for (User::const_op_iterator I = GEPOp->op_begin()+1,
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E = GEPOp->op_end(); I != E; ++I) {
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Value *Index = *I;
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// Compute the (potentially symbolic) offset in bytes for this index.
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if (StructType *STy = dyn_cast<StructType>(*GTI++)) {
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// For a struct, add the member offset.
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unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
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if (FieldNo == 0) continue;
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BaseOffs += DL->getStructLayout(STy)->getElementOffset(FieldNo);
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continue;
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}
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// For an array/pointer, add the element offset, explicitly scaled.
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if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
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if (CIdx->isZero()) continue;
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BaseOffs += DL->getTypeAllocSize(*GTI)*CIdx->getSExtValue();
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continue;
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}
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uint64_t Scale = DL->getTypeAllocSize(*GTI);
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ExtensionKind Extension = EK_NotExtended;
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// If the integer type is smaller than the pointer size, it is implicitly
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// sign extended to pointer size.
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unsigned Width = Index->getType()->getIntegerBitWidth();
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if (DL->getPointerSizeInBits(AS) > Width)
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Extension = EK_SignExt;
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// Use GetLinearExpression to decompose the index into a C1*V+C2 form.
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APInt IndexScale(Width, 0), IndexOffset(Width, 0);
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Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension,
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*DL, 0, AC, DT);
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// The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
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// This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
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BaseOffs += IndexOffset.getSExtValue()*Scale;
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Scale *= IndexScale.getSExtValue();
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// If we already had an occurrence of this index variable, merge this
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// scale into it. For example, we want to handle:
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// A[x][x] -> x*16 + x*4 -> x*20
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// This also ensures that 'x' only appears in the index list once.
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for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
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if (VarIndices[i].V == Index &&
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VarIndices[i].Extension == Extension) {
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Scale += VarIndices[i].Scale;
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VarIndices.erase(VarIndices.begin()+i);
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break;
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}
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}
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// Make sure that we have a scale that makes sense for this target's
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// pointer size.
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if (unsigned ShiftBits = 64 - DL->getPointerSizeInBits(AS)) {
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Scale <<= ShiftBits;
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Scale = (int64_t)Scale >> ShiftBits;
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}
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if (Scale) {
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VariableGEPIndex Entry = {Index, Extension,
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static_cast<int64_t>(Scale)};
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VarIndices.push_back(Entry);
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}
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}
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// Analyze the base pointer next.
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V = GEPOp->getOperand(0);
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} while (--MaxLookup);
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// If the chain of expressions is too deep, just return early.
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MaxLookupReached = true;
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return V;
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}
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|
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//===----------------------------------------------------------------------===//
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// BasicAliasAnalysis Pass
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//===----------------------------------------------------------------------===//
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|
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#ifndef NDEBUG
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static const Function *getParent(const Value *V) {
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if (const Instruction *inst = dyn_cast<Instruction>(V))
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return inst->getParent()->getParent();
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if (const Argument *arg = dyn_cast<Argument>(V))
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return arg->getParent();
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return nullptr;
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}
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static bool notDifferentParent(const Value *O1, const Value *O2) {
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const Function *F1 = getParent(O1);
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const Function *F2 = getParent(O2);
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return !F1 || !F2 || F1 == F2;
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}
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#endif
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namespace {
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/// BasicAliasAnalysis - This is the primary alias analysis implementation.
|
|
struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
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static char ID; // Class identification, replacement for typeinfo
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BasicAliasAnalysis() : ImmutablePass(ID) {
|
|
initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
|
|
}
|
|
|
|
void initializePass() override {
|
|
InitializeAliasAnalysis(this);
|
|
}
|
|
|
|
void getAnalysisUsage(AnalysisUsage &AU) const override {
|
|
AU.addRequired<AliasAnalysis>();
|
|
AU.addRequired<AssumptionCacheTracker>();
|
|
AU.addRequired<TargetLibraryInfoWrapperPass>();
|
|
}
|
|
|
|
AliasResult alias(const Location &LocA, const Location &LocB) override {
|
|
assert(AliasCache.empty() && "AliasCache must be cleared after use!");
|
|
assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
|
|
"BasicAliasAnalysis doesn't support interprocedural queries.");
|
|
AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.AATags,
|
|
LocB.Ptr, LocB.Size, LocB.AATags);
|
|
// AliasCache rarely has more than 1 or 2 elements, always use
|
|
// shrink_and_clear so it quickly returns to the inline capacity of the
|
|
// SmallDenseMap if it ever grows larger.
|
|
// FIXME: This should really be shrink_to_inline_capacity_and_clear().
|
|
AliasCache.shrink_and_clear();
|
|
VisitedPhiBBs.clear();
|
|
return Alias;
|
|
}
|
|
|
|
ModRefResult getModRefInfo(ImmutableCallSite CS,
|
|
const Location &Loc) override;
|
|
|
|
ModRefResult getModRefInfo(ImmutableCallSite CS1,
|
|
ImmutableCallSite CS2) override;
|
|
|
|
/// pointsToConstantMemory - Chase pointers until we find a (constant
|
|
/// global) or not.
|
|
bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override;
|
|
|
|
/// Get the location associated with a pointer argument of a callsite.
|
|
Location getArgLocation(ImmutableCallSite CS, unsigned ArgIdx,
|
|
ModRefResult &Mask) override;
|
|
|
|
/// getModRefBehavior - Return the behavior when calling the given
|
|
/// call site.
|
|
ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override;
|
|
|
|
/// getModRefBehavior - Return the behavior when calling the given function.
|
|
/// For use when the call site is not known.
|
|
ModRefBehavior getModRefBehavior(const Function *F) override;
|
|
|
|
/// getAdjustedAnalysisPointer - This method is used when a pass implements
|
|
/// an analysis interface through multiple inheritance. If needed, it
|
|
/// should override this to adjust the this pointer as needed for the
|
|
/// specified pass info.
|
|
void *getAdjustedAnalysisPointer(const void *ID) override {
|
|
if (ID == &AliasAnalysis::ID)
|
|
return (AliasAnalysis*)this;
|
|
return this;
|
|
}
|
|
|
|
private:
|
|
// AliasCache - Track alias queries to guard against recursion.
|
|
typedef std::pair<Location, Location> LocPair;
|
|
typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
|
|
AliasCacheTy AliasCache;
|
|
|
|
/// \brief Track phi nodes we have visited. When interpret "Value" pointer
|
|
/// equality as value equality we need to make sure that the "Value" is not
|
|
/// part of a cycle. Otherwise, two uses could come from different
|
|
/// "iterations" of a cycle and see different values for the same "Value"
|
|
/// pointer.
|
|
/// The following example shows the problem:
|
|
/// %p = phi(%alloca1, %addr2)
|
|
/// %l = load %ptr
|
|
/// %addr1 = gep, %alloca2, 0, %l
|
|
/// %addr2 = gep %alloca2, 0, (%l + 1)
|
|
/// alias(%p, %addr1) -> MayAlias !
|
|
/// store %l, ...
|
|
SmallPtrSet<const BasicBlock*, 8> VisitedPhiBBs;
|
|
|
|
// Visited - Track instructions visited by pointsToConstantMemory.
|
|
SmallPtrSet<const Value*, 16> Visited;
|
|
|
|
/// \brief Check whether two Values can be considered equivalent.
|
|
///
|
|
/// In addition to pointer equivalence of \p V1 and \p V2 this checks
|
|
/// whether they can not be part of a cycle in the value graph by looking at
|
|
/// all visited phi nodes an making sure that the phis cannot reach the
|
|
/// value. We have to do this because we are looking through phi nodes (That
|
|
/// is we say noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB).
|
|
bool isValueEqualInPotentialCycles(const Value *V1, const Value *V2);
|
|
|
|
/// \brief Dest and Src are the variable indices from two decomposed
|
|
/// GetElementPtr instructions GEP1 and GEP2 which have common base
|
|
/// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
|
|
/// difference between the two pointers.
|
|
void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
|
|
const SmallVectorImpl<VariableGEPIndex> &Src);
|
|
|
|
// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
|
|
// instruction against another.
|
|
AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
|
|
const AAMDNodes &V1AAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo,
|
|
const Value *UnderlyingV1, const Value *UnderlyingV2);
|
|
|
|
// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI
|
|
// instruction against another.
|
|
AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
|
|
const AAMDNodes &PNAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo);
|
|
|
|
/// aliasSelect - Disambiguate a Select instruction against another value.
|
|
AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
|
|
const AAMDNodes &SIAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo);
|
|
|
|
AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
|
|
AAMDNodes V1AATag,
|
|
const Value *V2, uint64_t V2Size,
|
|
AAMDNodes V2AATag);
|
|
};
|
|
} // End of anonymous namespace
|
|
|
|
// Register this pass...
|
|
char BasicAliasAnalysis::ID = 0;
|
|
INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
|
|
"Basic Alias Analysis (stateless AA impl)",
|
|
false, true, false)
|
|
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
|
|
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
|
|
INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
|
|
"Basic Alias Analysis (stateless AA impl)",
|
|
false, true, false)
|
|
|
|
|
|
ImmutablePass *llvm::createBasicAliasAnalysisPass() {
|
|
return new BasicAliasAnalysis();
|
|
}
|
|
|
|
/// pointsToConstantMemory - Returns whether the given pointer value
|
|
/// points to memory that is local to the function, with global constants being
|
|
/// considered local to all functions.
|
|
bool
|
|
BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) {
|
|
assert(Visited.empty() && "Visited must be cleared after use!");
|
|
|
|
unsigned MaxLookup = 8;
|
|
SmallVector<const Value *, 16> Worklist;
|
|
Worklist.push_back(Loc.Ptr);
|
|
do {
|
|
const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), DL);
|
|
if (!Visited.insert(V).second) {
|
|
Visited.clear();
|
|
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
|
|
}
|
|
|
|
// An alloca instruction defines local memory.
|
|
if (OrLocal && isa<AllocaInst>(V))
|
|
continue;
|
|
|
|
// A global constant counts as local memory for our purposes.
|
|
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
|
|
// Note: this doesn't require GV to be "ODR" because it isn't legal for a
|
|
// global to be marked constant in some modules and non-constant in
|
|
// others. GV may even be a declaration, not a definition.
|
|
if (!GV->isConstant()) {
|
|
Visited.clear();
|
|
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
|
|
}
|
|
continue;
|
|
}
|
|
|
|
// If both select values point to local memory, then so does the select.
|
|
if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
|
|
Worklist.push_back(SI->getTrueValue());
|
|
Worklist.push_back(SI->getFalseValue());
|
|
continue;
|
|
}
|
|
|
|
// If all values incoming to a phi node point to local memory, then so does
|
|
// the phi.
|
|
if (const PHINode *PN = dyn_cast<PHINode>(V)) {
|
|
// Don't bother inspecting phi nodes with many operands.
|
|
if (PN->getNumIncomingValues() > MaxLookup) {
|
|
Visited.clear();
|
|
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
|
|
}
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
|
|
Worklist.push_back(PN->getIncomingValue(i));
|
|
continue;
|
|
}
|
|
|
|
// Otherwise be conservative.
|
|
Visited.clear();
|
|
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
|
|
|
|
} while (!Worklist.empty() && --MaxLookup);
|
|
|
|
Visited.clear();
|
|
return Worklist.empty();
|
|
}
|
|
|
|
static bool isMemsetPattern16(const Function *MS,
|
|
const TargetLibraryInfo &TLI) {
|
|
if (TLI.has(LibFunc::memset_pattern16) &&
|
|
MS->getName() == "memset_pattern16") {
|
|
FunctionType *MemsetType = MS->getFunctionType();
|
|
if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 &&
|
|
isa<PointerType>(MemsetType->getParamType(0)) &&
|
|
isa<PointerType>(MemsetType->getParamType(1)) &&
|
|
isa<IntegerType>(MemsetType->getParamType(2)))
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// getModRefBehavior - Return the behavior when calling the given call site.
|
|
AliasAnalysis::ModRefBehavior
|
|
BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
|
|
if (CS.doesNotAccessMemory())
|
|
// Can't do better than this.
|
|
return DoesNotAccessMemory;
|
|
|
|
ModRefBehavior Min = UnknownModRefBehavior;
|
|
|
|
// If the callsite knows it only reads memory, don't return worse
|
|
// than that.
|
|
if (CS.onlyReadsMemory())
|
|
Min = OnlyReadsMemory;
|
|
|
|
// The AliasAnalysis base class has some smarts, lets use them.
|
|
return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
|
|
}
|
|
|
|
/// getModRefBehavior - Return the behavior when calling the given function.
|
|
/// For use when the call site is not known.
|
|
AliasAnalysis::ModRefBehavior
|
|
BasicAliasAnalysis::getModRefBehavior(const Function *F) {
|
|
// If the function declares it doesn't access memory, we can't do better.
|
|
if (F->doesNotAccessMemory())
|
|
return DoesNotAccessMemory;
|
|
|
|
// For intrinsics, we can check the table.
|
|
if (unsigned iid = F->getIntrinsicID()) {
|
|
#define GET_INTRINSIC_MODREF_BEHAVIOR
|
|
#include "llvm/IR/Intrinsics.gen"
|
|
#undef GET_INTRINSIC_MODREF_BEHAVIOR
|
|
}
|
|
|
|
ModRefBehavior Min = UnknownModRefBehavior;
|
|
|
|
// If the function declares it only reads memory, go with that.
|
|
if (F->onlyReadsMemory())
|
|
Min = OnlyReadsMemory;
|
|
|
|
const TargetLibraryInfo &TLI =
|
|
getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
|
|
if (isMemsetPattern16(F, TLI))
|
|
Min = OnlyAccessesArgumentPointees;
|
|
|
|
// Otherwise be conservative.
|
|
return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
|
|
}
|
|
|
|
AliasAnalysis::Location
|
|
BasicAliasAnalysis::getArgLocation(ImmutableCallSite CS, unsigned ArgIdx,
|
|
ModRefResult &Mask) {
|
|
Location Loc = AliasAnalysis::getArgLocation(CS, ArgIdx, Mask);
|
|
const TargetLibraryInfo &TLI =
|
|
getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
|
|
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
|
|
if (II != nullptr)
|
|
switch (II->getIntrinsicID()) {
|
|
default: break;
|
|
case Intrinsic::memset:
|
|
case Intrinsic::memcpy:
|
|
case Intrinsic::memmove: {
|
|
assert((ArgIdx == 0 || ArgIdx == 1) &&
|
|
"Invalid argument index for memory intrinsic");
|
|
if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
|
|
Loc.Size = LenCI->getZExtValue();
|
|
assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
|
|
"Memory intrinsic location pointer not argument?");
|
|
Mask = ArgIdx ? Ref : Mod;
|
|
break;
|
|
}
|
|
case Intrinsic::lifetime_start:
|
|
case Intrinsic::lifetime_end:
|
|
case Intrinsic::invariant_start: {
|
|
assert(ArgIdx == 1 && "Invalid argument index");
|
|
assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
|
|
"Intrinsic location pointer not argument?");
|
|
Loc.Size = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
|
|
break;
|
|
}
|
|
case Intrinsic::invariant_end: {
|
|
assert(ArgIdx == 2 && "Invalid argument index");
|
|
assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
|
|
"Intrinsic location pointer not argument?");
|
|
Loc.Size = cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
|
|
break;
|
|
}
|
|
case Intrinsic::arm_neon_vld1: {
|
|
assert(ArgIdx == 0 && "Invalid argument index");
|
|
assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
|
|
"Intrinsic location pointer not argument?");
|
|
// LLVM's vld1 and vst1 intrinsics currently only support a single
|
|
// vector register.
|
|
if (DL)
|
|
Loc.Size = DL->getTypeStoreSize(II->getType());
|
|
break;
|
|
}
|
|
case Intrinsic::arm_neon_vst1: {
|
|
assert(ArgIdx == 0 && "Invalid argument index");
|
|
assert(Loc.Ptr == II->getArgOperand(ArgIdx) &&
|
|
"Intrinsic location pointer not argument?");
|
|
if (DL)
|
|
Loc.Size = DL->getTypeStoreSize(II->getArgOperand(1)->getType());
|
|
break;
|
|
}
|
|
}
|
|
|
|
// We can bound the aliasing properties of memset_pattern16 just as we can
|
|
// for memcpy/memset. This is particularly important because the
|
|
// LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
|
|
// whenever possible.
|
|
else if (CS.getCalledFunction() &&
|
|
isMemsetPattern16(CS.getCalledFunction(), TLI)) {
|
|
assert((ArgIdx == 0 || ArgIdx == 1) &&
|
|
"Invalid argument index for memset_pattern16");
|
|
if (ArgIdx == 1)
|
|
Loc.Size = 16;
|
|
else if (const ConstantInt *LenCI =
|
|
dyn_cast<ConstantInt>(CS.getArgument(2)))
|
|
Loc.Size = LenCI->getZExtValue();
|
|
assert(Loc.Ptr == CS.getArgument(ArgIdx) &&
|
|
"memset_pattern16 location pointer not argument?");
|
|
Mask = ArgIdx ? Ref : Mod;
|
|
}
|
|
// FIXME: Handle memset_pattern4 and memset_pattern8 also.
|
|
|
|
return Loc;
|
|
}
|
|
|
|
static bool isAssumeIntrinsic(ImmutableCallSite CS) {
|
|
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
|
|
if (II && II->getIntrinsicID() == Intrinsic::assume)
|
|
return true;
|
|
|
|
return false;
|
|
}
|
|
|
|
/// getModRefInfo - Check to see if the specified callsite can clobber the
|
|
/// specified memory object. Since we only look at local properties of this
|
|
/// function, we really can't say much about this query. We do, however, use
|
|
/// simple "address taken" analysis on local objects.
|
|
AliasAnalysis::ModRefResult
|
|
BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
|
|
const Location &Loc) {
|
|
assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
|
|
"AliasAnalysis query involving multiple functions!");
|
|
|
|
const Value *Object = GetUnderlyingObject(Loc.Ptr, DL);
|
|
|
|
// If this is a tail call and Loc.Ptr points to a stack location, we know that
|
|
// the tail call cannot access or modify the local stack.
|
|
// We cannot exclude byval arguments here; these belong to the caller of
|
|
// the current function not to the current function, and a tail callee
|
|
// may reference them.
|
|
if (isa<AllocaInst>(Object))
|
|
if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
|
|
if (CI->isTailCall())
|
|
return NoModRef;
|
|
|
|
// If the pointer is to a locally allocated object that does not escape,
|
|
// then the call can not mod/ref the pointer unless the call takes the pointer
|
|
// as an argument, and itself doesn't capture it.
|
|
if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
|
|
isNonEscapingLocalObject(Object)) {
|
|
bool PassedAsArg = false;
|
|
unsigned ArgNo = 0;
|
|
for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
|
|
CI != CE; ++CI, ++ArgNo) {
|
|
// Only look at the no-capture or byval pointer arguments. If this
|
|
// pointer were passed to arguments that were neither of these, then it
|
|
// couldn't be no-capture.
|
|
if (!(*CI)->getType()->isPointerTy() ||
|
|
(!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
|
|
continue;
|
|
|
|
// If this is a no-capture pointer argument, see if we can tell that it
|
|
// is impossible to alias the pointer we're checking. If not, we have to
|
|
// assume that the call could touch the pointer, even though it doesn't
|
|
// escape.
|
|
if (!isNoAlias(Location(*CI), Location(Object))) {
|
|
PassedAsArg = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (!PassedAsArg)
|
|
return NoModRef;
|
|
}
|
|
|
|
// While the assume intrinsic is marked as arbitrarily writing so that
|
|
// proper control dependencies will be maintained, it never aliases any
|
|
// particular memory location.
|
|
if (isAssumeIntrinsic(CS))
|
|
return NoModRef;
|
|
|
|
// The AliasAnalysis base class has some smarts, lets use them.
|
|
return AliasAnalysis::getModRefInfo(CS, Loc);
|
|
}
|
|
|
|
AliasAnalysis::ModRefResult
|
|
BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
|
|
ImmutableCallSite CS2) {
|
|
// While the assume intrinsic is marked as arbitrarily writing so that
|
|
// proper control dependencies will be maintained, it never aliases any
|
|
// particular memory location.
|
|
if (isAssumeIntrinsic(CS1) || isAssumeIntrinsic(CS2))
|
|
return NoModRef;
|
|
|
|
// The AliasAnalysis base class has some smarts, lets use them.
|
|
return AliasAnalysis::getModRefInfo(CS1, CS2);
|
|
}
|
|
|
|
/// \brief Provide ad-hoc rules to disambiguate accesses through two GEP
|
|
/// operators, both having the exact same pointer operand.
|
|
static AliasAnalysis::AliasResult
|
|
aliasSameBasePointerGEPs(const GEPOperator *GEP1, uint64_t V1Size,
|
|
const GEPOperator *GEP2, uint64_t V2Size,
|
|
const DataLayout &DL) {
|
|
|
|
assert(GEP1->getPointerOperand() == GEP2->getPointerOperand() &&
|
|
"Expected GEPs with the same pointer operand");
|
|
|
|
// Try to determine whether GEP1 and GEP2 index through arrays, into structs,
|
|
// such that the struct field accesses provably cannot alias.
|
|
// We also need at least two indices (the pointer, and the struct field).
|
|
if (GEP1->getNumIndices() != GEP2->getNumIndices() ||
|
|
GEP1->getNumIndices() < 2)
|
|
return AliasAnalysis::MayAlias;
|
|
|
|
// If we don't know the size of the accesses through both GEPs, we can't
|
|
// determine whether the struct fields accessed can't alias.
|
|
if (V1Size == AliasAnalysis::UnknownSize ||
|
|
V2Size == AliasAnalysis::UnknownSize)
|
|
return AliasAnalysis::MayAlias;
|
|
|
|
ConstantInt *C1 =
|
|
dyn_cast<ConstantInt>(GEP1->getOperand(GEP1->getNumOperands() - 1));
|
|
ConstantInt *C2 =
|
|
dyn_cast<ConstantInt>(GEP2->getOperand(GEP2->getNumOperands() - 1));
|
|
|
|
// If the last (struct) indices aren't constants, we can't say anything.
|
|
// If they're identical, the other indices might be also be dynamically
|
|
// equal, so the GEPs can alias.
|
|
if (!C1 || !C2 || C1 == C2)
|
|
return AliasAnalysis::MayAlias;
|
|
|
|
// Find the last-indexed type of the GEP, i.e., the type you'd get if
|
|
// you stripped the last index.
|
|
// On the way, look at each indexed type. If there's something other
|
|
// than an array, different indices can lead to different final types.
|
|
SmallVector<Value *, 8> IntermediateIndices;
|
|
|
|
// Insert the first index; we don't need to check the type indexed
|
|
// through it as it only drops the pointer indirection.
|
|
assert(GEP1->getNumIndices() > 1 && "Not enough GEP indices to examine");
|
|
IntermediateIndices.push_back(GEP1->getOperand(1));
|
|
|
|
// Insert all the remaining indices but the last one.
|
|
// Also, check that they all index through arrays.
|
|
for (unsigned i = 1, e = GEP1->getNumIndices() - 1; i != e; ++i) {
|
|
if (!isa<ArrayType>(GetElementPtrInst::getIndexedType(
|
|
GEP1->getPointerOperandType(), IntermediateIndices)))
|
|
return AliasAnalysis::MayAlias;
|
|
IntermediateIndices.push_back(GEP1->getOperand(i + 1));
|
|
}
|
|
|
|
StructType *LastIndexedStruct =
|
|
dyn_cast<StructType>(GetElementPtrInst::getIndexedType(
|
|
GEP1->getPointerOperandType(), IntermediateIndices));
|
|
|
|
if (!LastIndexedStruct)
|
|
return AliasAnalysis::MayAlias;
|
|
|
|
// We know that:
|
|
// - both GEPs begin indexing from the exact same pointer;
|
|
// - the last indices in both GEPs are constants, indexing into a struct;
|
|
// - said indices are different, hence, the pointed-to fields are different;
|
|
// - both GEPs only index through arrays prior to that.
|
|
//
|
|
// This lets us determine that the struct that GEP1 indexes into and the
|
|
// struct that GEP2 indexes into must either precisely overlap or be
|
|
// completely disjoint. Because they cannot partially overlap, indexing into
|
|
// different non-overlapping fields of the struct will never alias.
|
|
|
|
// Therefore, the only remaining thing needed to show that both GEPs can't
|
|
// alias is that the fields are not overlapping.
|
|
const StructLayout *SL = DL.getStructLayout(LastIndexedStruct);
|
|
const uint64_t StructSize = SL->getSizeInBytes();
|
|
const uint64_t V1Off = SL->getElementOffset(C1->getZExtValue());
|
|
const uint64_t V2Off = SL->getElementOffset(C2->getZExtValue());
|
|
|
|
auto EltsDontOverlap = [StructSize](uint64_t V1Off, uint64_t V1Size,
|
|
uint64_t V2Off, uint64_t V2Size) {
|
|
return V1Off < V2Off && V1Off + V1Size <= V2Off &&
|
|
((V2Off + V2Size <= StructSize) ||
|
|
(V2Off + V2Size - StructSize <= V1Off));
|
|
};
|
|
|
|
if (EltsDontOverlap(V1Off, V1Size, V2Off, V2Size) ||
|
|
EltsDontOverlap(V2Off, V2Size, V1Off, V1Size))
|
|
return AliasAnalysis::NoAlias;
|
|
|
|
return AliasAnalysis::MayAlias;
|
|
}
|
|
|
|
/// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
|
|
/// against another pointer. We know that V1 is a GEP, but we don't know
|
|
/// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, DL),
|
|
/// UnderlyingV2 is the same for V2.
|
|
///
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
|
|
const AAMDNodes &V1AAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo,
|
|
const Value *UnderlyingV1,
|
|
const Value *UnderlyingV2) {
|
|
int64_t GEP1BaseOffset;
|
|
bool GEP1MaxLookupReached;
|
|
SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
|
|
|
|
// We have to get two AssumptionCaches here because GEP1 and V2 may be from
|
|
// different functions.
|
|
// FIXME: This really doesn't make any sense. We get a dominator tree below
|
|
// that can only refer to a single function. But this function (aliasGEP) is
|
|
// a method on an immutable pass that can be called when there *isn't*
|
|
// a single function. The old pass management layer makes this "work", but
|
|
// this isn't really a clean solution.
|
|
AssumptionCacheTracker &ACT = getAnalysis<AssumptionCacheTracker>();
|
|
AssumptionCache *AC1 = nullptr, *AC2 = nullptr;
|
|
if (auto *GEP1I = dyn_cast<Instruction>(GEP1))
|
|
AC1 = &ACT.getAssumptionCache(
|
|
const_cast<Function &>(*GEP1I->getParent()->getParent()));
|
|
if (auto *I2 = dyn_cast<Instruction>(V2))
|
|
AC2 = &ACT.getAssumptionCache(
|
|
const_cast<Function &>(*I2->getParent()->getParent()));
|
|
|
|
DominatorTreeWrapperPass *DTWP =
|
|
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
|
|
DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
|
|
|
|
// If we have two gep instructions with must-alias or not-alias'ing base
|
|
// pointers, figure out if the indexes to the GEP tell us anything about the
|
|
// derived pointer.
|
|
if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
|
|
// Do the base pointers alias?
|
|
AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, AAMDNodes(),
|
|
UnderlyingV2, UnknownSize, AAMDNodes());
|
|
|
|
// Check for geps of non-aliasing underlying pointers where the offsets are
|
|
// identical.
|
|
if ((BaseAlias == MayAlias) && V1Size == V2Size) {
|
|
// Do the base pointers alias assuming type and size.
|
|
AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
|
|
V1AAInfo, UnderlyingV2,
|
|
V2Size, V2AAInfo);
|
|
if (PreciseBaseAlias == NoAlias) {
|
|
// See if the computed offset from the common pointer tells us about the
|
|
// relation of the resulting pointer.
|
|
int64_t GEP2BaseOffset;
|
|
bool GEP2MaxLookupReached;
|
|
SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
|
|
const Value *GEP2BasePtr =
|
|
DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
|
|
GEP2MaxLookupReached, DL, AC2, DT);
|
|
const Value *GEP1BasePtr =
|
|
DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
|
|
GEP1MaxLookupReached, DL, AC1, DT);
|
|
// DecomposeGEPExpression and GetUnderlyingObject should return the
|
|
// same result except when DecomposeGEPExpression has no DataLayout.
|
|
if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
|
|
assert(!DL &&
|
|
"DecomposeGEPExpression and GetUnderlyingObject disagree!");
|
|
return MayAlias;
|
|
}
|
|
// If the max search depth is reached the result is undefined
|
|
if (GEP2MaxLookupReached || GEP1MaxLookupReached)
|
|
return MayAlias;
|
|
|
|
// Same offsets.
|
|
if (GEP1BaseOffset == GEP2BaseOffset &&
|
|
GEP1VariableIndices == GEP2VariableIndices)
|
|
return NoAlias;
|
|
GEP1VariableIndices.clear();
|
|
}
|
|
}
|
|
|
|
// If we get a No or May, then return it immediately, no amount of analysis
|
|
// will improve this situation.
|
|
if (BaseAlias != MustAlias) return BaseAlias;
|
|
|
|
// Otherwise, we have a MustAlias. Since the base pointers alias each other
|
|
// exactly, see if the computed offset from the common pointer tells us
|
|
// about the relation of the resulting pointer.
|
|
const Value *GEP1BasePtr =
|
|
DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
|
|
GEP1MaxLookupReached, DL, AC1, DT);
|
|
|
|
int64_t GEP2BaseOffset;
|
|
bool GEP2MaxLookupReached;
|
|
SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
|
|
const Value *GEP2BasePtr =
|
|
DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
|
|
GEP2MaxLookupReached, DL, AC2, DT);
|
|
|
|
// DecomposeGEPExpression and GetUnderlyingObject should return the
|
|
// same result except when DecomposeGEPExpression has no DataLayout.
|
|
if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
|
|
assert(!DL &&
|
|
"DecomposeGEPExpression and GetUnderlyingObject disagree!");
|
|
return MayAlias;
|
|
}
|
|
|
|
// If we know the two GEPs are based off of the exact same pointer (and not
|
|
// just the same underlying object), see if that tells us anything about
|
|
// the resulting pointers.
|
|
if (DL && GEP1->getPointerOperand() == GEP2->getPointerOperand()) {
|
|
AliasResult R = aliasSameBasePointerGEPs(GEP1, V1Size, GEP2, V2Size, *DL);
|
|
// If we couldn't find anything interesting, don't abandon just yet.
|
|
if (R != MayAlias)
|
|
return R;
|
|
}
|
|
|
|
// If the max search depth is reached the result is undefined
|
|
if (GEP2MaxLookupReached || GEP1MaxLookupReached)
|
|
return MayAlias;
|
|
|
|
// Subtract the GEP2 pointer from the GEP1 pointer to find out their
|
|
// symbolic difference.
|
|
GEP1BaseOffset -= GEP2BaseOffset;
|
|
GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
|
|
|
|
} else {
|
|
// Check to see if these two pointers are related by the getelementptr
|
|
// instruction. If one pointer is a GEP with a non-zero index of the other
|
|
// pointer, we know they cannot alias.
|
|
|
|
// If both accesses are unknown size, we can't do anything useful here.
|
|
if (V1Size == UnknownSize && V2Size == UnknownSize)
|
|
return MayAlias;
|
|
|
|
AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, AAMDNodes(),
|
|
V2, V2Size, V2AAInfo);
|
|
if (R != MustAlias)
|
|
// If V2 may alias GEP base pointer, conservatively returns MayAlias.
|
|
// If V2 is known not to alias GEP base pointer, then the two values
|
|
// cannot alias per GEP semantics: "A pointer value formed from a
|
|
// getelementptr instruction is associated with the addresses associated
|
|
// with the first operand of the getelementptr".
|
|
return R;
|
|
|
|
const Value *GEP1BasePtr =
|
|
DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
|
|
GEP1MaxLookupReached, DL, AC1, DT);
|
|
|
|
// DecomposeGEPExpression and GetUnderlyingObject should return the
|
|
// same result except when DecomposeGEPExpression has no DataLayout.
|
|
if (GEP1BasePtr != UnderlyingV1) {
|
|
assert(!DL &&
|
|
"DecomposeGEPExpression and GetUnderlyingObject disagree!");
|
|
return MayAlias;
|
|
}
|
|
// If the max search depth is reached the result is undefined
|
|
if (GEP1MaxLookupReached)
|
|
return MayAlias;
|
|
}
|
|
|
|
// In the two GEP Case, if there is no difference in the offsets of the
|
|
// computed pointers, the resultant pointers are a must alias. This
|
|
// hapens when we have two lexically identical GEP's (for example).
|
|
//
|
|
// In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
|
|
// must aliases the GEP, the end result is a must alias also.
|
|
if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
|
|
return MustAlias;
|
|
|
|
// If there is a constant difference between the pointers, but the difference
|
|
// is less than the size of the associated memory object, then we know
|
|
// that the objects are partially overlapping. If the difference is
|
|
// greater, we know they do not overlap.
|
|
if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) {
|
|
if (GEP1BaseOffset >= 0) {
|
|
if (V2Size != UnknownSize) {
|
|
if ((uint64_t)GEP1BaseOffset < V2Size)
|
|
return PartialAlias;
|
|
return NoAlias;
|
|
}
|
|
} else {
|
|
// We have the situation where:
|
|
// + +
|
|
// | BaseOffset |
|
|
// ---------------->|
|
|
// |-->V1Size |-------> V2Size
|
|
// GEP1 V2
|
|
// We need to know that V2Size is not unknown, otherwise we might have
|
|
// stripped a gep with negative index ('gep <ptr>, -1, ...).
|
|
if (V1Size != UnknownSize && V2Size != UnknownSize) {
|
|
if (-(uint64_t)GEP1BaseOffset < V1Size)
|
|
return PartialAlias;
|
|
return NoAlias;
|
|
}
|
|
}
|
|
}
|
|
|
|
if (!GEP1VariableIndices.empty()) {
|
|
uint64_t Modulo = 0;
|
|
bool AllPositive = true;
|
|
for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i) {
|
|
|
|
// Try to distinguish something like &A[i][1] against &A[42][0].
|
|
// Grab the least significant bit set in any of the scales. We
|
|
// don't need std::abs here (even if the scale's negative) as we'll
|
|
// be ^'ing Modulo with itself later.
|
|
Modulo |= (uint64_t) GEP1VariableIndices[i].Scale;
|
|
|
|
if (AllPositive) {
|
|
// If the Value could change between cycles, then any reasoning about
|
|
// the Value this cycle may not hold in the next cycle. We'll just
|
|
// give up if we can't determine conditions that hold for every cycle:
|
|
const Value *V = GEP1VariableIndices[i].V;
|
|
|
|
bool SignKnownZero, SignKnownOne;
|
|
ComputeSignBit(const_cast<Value *>(V), SignKnownZero, SignKnownOne, DL,
|
|
0, AC1, nullptr, DT);
|
|
|
|
// Zero-extension widens the variable, and so forces the sign
|
|
// bit to zero.
|
|
bool IsZExt = GEP1VariableIndices[i].Extension == EK_ZeroExt;
|
|
SignKnownZero |= IsZExt;
|
|
SignKnownOne &= !IsZExt;
|
|
|
|
// If the variable begins with a zero then we know it's
|
|
// positive, regardless of whether the value is signed or
|
|
// unsigned.
|
|
int64_t Scale = GEP1VariableIndices[i].Scale;
|
|
AllPositive =
|
|
(SignKnownZero && Scale >= 0) ||
|
|
(SignKnownOne && Scale < 0);
|
|
}
|
|
}
|
|
|
|
Modulo = Modulo ^ (Modulo & (Modulo - 1));
|
|
|
|
// We can compute the difference between the two addresses
|
|
// mod Modulo. Check whether that difference guarantees that the
|
|
// two locations do not alias.
|
|
uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
|
|
if (V1Size != UnknownSize && V2Size != UnknownSize &&
|
|
ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
|
|
return NoAlias;
|
|
|
|
// If we know all the variables are positive, then GEP1 >= GEP1BasePtr.
|
|
// If GEP1BasePtr > V2 (GEP1BaseOffset > 0) then we know the pointers
|
|
// don't alias if V2Size can fit in the gap between V2 and GEP1BasePtr.
|
|
if (AllPositive && GEP1BaseOffset > 0 && V2Size <= (uint64_t) GEP1BaseOffset)
|
|
return NoAlias;
|
|
}
|
|
|
|
// Statically, we can see that the base objects are the same, but the
|
|
// pointers have dynamic offsets which we can't resolve. And none of our
|
|
// little tricks above worked.
|
|
//
|
|
// TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
|
|
// practical effect of this is protecting TBAA in the case of dynamic
|
|
// indices into arrays of unions or malloc'd memory.
|
|
return PartialAlias;
|
|
}
|
|
|
|
static AliasAnalysis::AliasResult
|
|
MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
|
|
// If the results agree, take it.
|
|
if (A == B)
|
|
return A;
|
|
// A mix of PartialAlias and MustAlias is PartialAlias.
|
|
if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
|
|
(B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
|
|
return AliasAnalysis::PartialAlias;
|
|
// Otherwise, we don't know anything.
|
|
return AliasAnalysis::MayAlias;
|
|
}
|
|
|
|
/// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
|
|
/// instruction against another.
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
|
|
const AAMDNodes &SIAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo) {
|
|
// If the values are Selects with the same condition, we can do a more precise
|
|
// check: just check for aliases between the values on corresponding arms.
|
|
if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
|
|
if (SI->getCondition() == SI2->getCondition()) {
|
|
AliasResult Alias =
|
|
aliasCheck(SI->getTrueValue(), SISize, SIAAInfo,
|
|
SI2->getTrueValue(), V2Size, V2AAInfo);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
AliasResult ThisAlias =
|
|
aliasCheck(SI->getFalseValue(), SISize, SIAAInfo,
|
|
SI2->getFalseValue(), V2Size, V2AAInfo);
|
|
return MergeAliasResults(ThisAlias, Alias);
|
|
}
|
|
|
|
// If both arms of the Select node NoAlias or MustAlias V2, then returns
|
|
// NoAlias / MustAlias. Otherwise, returns MayAlias.
|
|
AliasResult Alias =
|
|
aliasCheck(V2, V2Size, V2AAInfo, SI->getTrueValue(), SISize, SIAAInfo);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
|
|
AliasResult ThisAlias =
|
|
aliasCheck(V2, V2Size, V2AAInfo, SI->getFalseValue(), SISize, SIAAInfo);
|
|
return MergeAliasResults(ThisAlias, Alias);
|
|
}
|
|
|
|
// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
|
|
// against another.
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
|
|
const AAMDNodes &PNAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const AAMDNodes &V2AAInfo) {
|
|
// Track phi nodes we have visited. We use this information when we determine
|
|
// value equivalence.
|
|
VisitedPhiBBs.insert(PN->getParent());
|
|
|
|
// If the values are PHIs in the same block, we can do a more precise
|
|
// as well as efficient check: just check for aliases between the values
|
|
// on corresponding edges.
|
|
if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
|
|
if (PN2->getParent() == PN->getParent()) {
|
|
LocPair Locs(Location(PN, PNSize, PNAAInfo),
|
|
Location(V2, V2Size, V2AAInfo));
|
|
if (PN > V2)
|
|
std::swap(Locs.first, Locs.second);
|
|
// Analyse the PHIs' inputs under the assumption that the PHIs are
|
|
// NoAlias.
|
|
// If the PHIs are May/MustAlias there must be (recursively) an input
|
|
// operand from outside the PHIs' cycle that is MayAlias/MustAlias or
|
|
// there must be an operation on the PHIs within the PHIs' value cycle
|
|
// that causes a MayAlias.
|
|
// Pretend the phis do not alias.
|
|
AliasResult Alias = NoAlias;
|
|
assert(AliasCache.count(Locs) &&
|
|
"There must exist an entry for the phi node");
|
|
AliasResult OrigAliasResult = AliasCache[Locs];
|
|
AliasCache[Locs] = NoAlias;
|
|
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
AliasResult ThisAlias =
|
|
aliasCheck(PN->getIncomingValue(i), PNSize, PNAAInfo,
|
|
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
|
|
V2Size, V2AAInfo);
|
|
Alias = MergeAliasResults(ThisAlias, Alias);
|
|
if (Alias == MayAlias)
|
|
break;
|
|
}
|
|
|
|
// Reset if speculation failed.
|
|
if (Alias != NoAlias)
|
|
AliasCache[Locs] = OrigAliasResult;
|
|
|
|
return Alias;
|
|
}
|
|
|
|
SmallPtrSet<Value*, 4> UniqueSrc;
|
|
SmallVector<Value*, 4> V1Srcs;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
Value *PV1 = PN->getIncomingValue(i);
|
|
if (isa<PHINode>(PV1))
|
|
// If any of the source itself is a PHI, return MayAlias conservatively
|
|
// to avoid compile time explosion. The worst possible case is if both
|
|
// sides are PHI nodes. In which case, this is O(m x n) time where 'm'
|
|
// and 'n' are the number of PHI sources.
|
|
return MayAlias;
|
|
if (UniqueSrc.insert(PV1).second)
|
|
V1Srcs.push_back(PV1);
|
|
}
|
|
|
|
AliasResult Alias = aliasCheck(V2, V2Size, V2AAInfo,
|
|
V1Srcs[0], PNSize, PNAAInfo);
|
|
// Early exit if the check of the first PHI source against V2 is MayAlias.
|
|
// Other results are not possible.
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
|
|
// If all sources of the PHI node NoAlias or MustAlias V2, then returns
|
|
// NoAlias / MustAlias. Otherwise, returns MayAlias.
|
|
for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
|
|
Value *V = V1Srcs[i];
|
|
|
|
AliasResult ThisAlias = aliasCheck(V2, V2Size, V2AAInfo,
|
|
V, PNSize, PNAAInfo);
|
|
Alias = MergeAliasResults(ThisAlias, Alias);
|
|
if (Alias == MayAlias)
|
|
break;
|
|
}
|
|
|
|
return Alias;
|
|
}
|
|
|
|
// aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
|
|
// such as array references.
|
|
//
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
|
|
AAMDNodes V1AAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
AAMDNodes V2AAInfo) {
|
|
// If either of the memory references is empty, it doesn't matter what the
|
|
// pointer values are.
|
|
if (V1Size == 0 || V2Size == 0)
|
|
return NoAlias;
|
|
|
|
// Strip off any casts if they exist.
|
|
V1 = V1->stripPointerCasts();
|
|
V2 = V2->stripPointerCasts();
|
|
|
|
// Are we checking for alias of the same value?
|
|
// Because we look 'through' phi nodes we could look at "Value" pointers from
|
|
// different iterations. We must therefore make sure that this is not the
|
|
// case. The function isValueEqualInPotentialCycles ensures that this cannot
|
|
// happen by looking at the visited phi nodes and making sure they cannot
|
|
// reach the value.
|
|
if (isValueEqualInPotentialCycles(V1, V2))
|
|
return MustAlias;
|
|
|
|
if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
|
|
return NoAlias; // Scalars cannot alias each other
|
|
|
|
// Figure out what objects these things are pointing to if we can.
|
|
const Value *O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth);
|
|
const Value *O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth);
|
|
|
|
// Null values in the default address space don't point to any object, so they
|
|
// don't alias any other pointer.
|
|
if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
|
|
if (CPN->getType()->getAddressSpace() == 0)
|
|
return NoAlias;
|
|
if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
|
|
if (CPN->getType()->getAddressSpace() == 0)
|
|
return NoAlias;
|
|
|
|
if (O1 != O2) {
|
|
// If V1/V2 point to two different objects we know that we have no alias.
|
|
if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
|
|
return NoAlias;
|
|
|
|
// Constant pointers can't alias with non-const isIdentifiedObject objects.
|
|
if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
|
|
(isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
|
|
return NoAlias;
|
|
|
|
// Function arguments can't alias with things that are known to be
|
|
// unambigously identified at the function level.
|
|
if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
|
|
(isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
|
|
return NoAlias;
|
|
|
|
// Most objects can't alias null.
|
|
if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
|
|
(isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
|
|
return NoAlias;
|
|
|
|
// If one pointer is the result of a call/invoke or load and the other is a
|
|
// non-escaping local object within the same function, then we know the
|
|
// object couldn't escape to a point where the call could return it.
|
|
//
|
|
// Note that if the pointers are in different functions, there are a
|
|
// variety of complications. A call with a nocapture argument may still
|
|
// temporary store the nocapture argument's value in a temporary memory
|
|
// location if that memory location doesn't escape. Or it may pass a
|
|
// nocapture value to other functions as long as they don't capture it.
|
|
if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
|
|
return NoAlias;
|
|
if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
|
|
return NoAlias;
|
|
}
|
|
|
|
// If the size of one access is larger than the entire object on the other
|
|
// side, then we know such behavior is undefined and can assume no alias.
|
|
if (DL)
|
|
if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *DL, *TLI)) ||
|
|
(V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *DL, *TLI)))
|
|
return NoAlias;
|
|
|
|
// Check the cache before climbing up use-def chains. This also terminates
|
|
// otherwise infinitely recursive queries.
|
|
LocPair Locs(Location(V1, V1Size, V1AAInfo),
|
|
Location(V2, V2Size, V2AAInfo));
|
|
if (V1 > V2)
|
|
std::swap(Locs.first, Locs.second);
|
|
std::pair<AliasCacheTy::iterator, bool> Pair =
|
|
AliasCache.insert(std::make_pair(Locs, MayAlias));
|
|
if (!Pair.second)
|
|
return Pair.first->second;
|
|
|
|
// FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
|
|
// GEP can't simplify, we don't even look at the PHI cases.
|
|
if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
std::swap(O1, O2);
|
|
std::swap(V1AAInfo, V2AAInfo);
|
|
}
|
|
if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
|
|
AliasResult Result = aliasGEP(GV1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O1, O2);
|
|
if (Result != MayAlias) return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
std::swap(V1AAInfo, V2AAInfo);
|
|
}
|
|
if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
|
|
AliasResult Result = aliasPHI(PN, V1Size, V1AAInfo,
|
|
V2, V2Size, V2AAInfo);
|
|
if (Result != MayAlias) return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
std::swap(V1AAInfo, V2AAInfo);
|
|
}
|
|
if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
|
|
AliasResult Result = aliasSelect(S1, V1Size, V1AAInfo,
|
|
V2, V2Size, V2AAInfo);
|
|
if (Result != MayAlias) return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
// If both pointers are pointing into the same object and one of them
|
|
// accesses is accessing the entire object, then the accesses must
|
|
// overlap in some way.
|
|
if (DL && O1 == O2)
|
|
if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *DL, *TLI)) ||
|
|
(V2Size != UnknownSize && isObjectSize(O2, V2Size, *DL, *TLI)))
|
|
return AliasCache[Locs] = PartialAlias;
|
|
|
|
AliasResult Result =
|
|
AliasAnalysis::alias(Location(V1, V1Size, V1AAInfo),
|
|
Location(V2, V2Size, V2AAInfo));
|
|
return AliasCache[Locs] = Result;
|
|
}
|
|
|
|
bool BasicAliasAnalysis::isValueEqualInPotentialCycles(const Value *V,
|
|
const Value *V2) {
|
|
if (V != V2)
|
|
return false;
|
|
|
|
const Instruction *Inst = dyn_cast<Instruction>(V);
|
|
if (!Inst)
|
|
return true;
|
|
|
|
if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck)
|
|
return false;
|
|
|
|
// Use dominance or loop info if available.
|
|
DominatorTreeWrapperPass *DTWP =
|
|
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
|
|
DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
|
|
auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
|
|
LoopInfo *LI = LIWP ? &LIWP->getLoopInfo() : nullptr;
|
|
|
|
// Make sure that the visited phis cannot reach the Value. This ensures that
|
|
// the Values cannot come from different iterations of a potential cycle the
|
|
// phi nodes could be involved in.
|
|
for (auto *P : VisitedPhiBBs)
|
|
if (isPotentiallyReachable(P->begin(), Inst, DT, LI))
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
/// GetIndexDifference - Dest and Src are the variable indices from two
|
|
/// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base
|
|
/// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
|
|
/// difference between the two pointers.
|
|
void BasicAliasAnalysis::GetIndexDifference(
|
|
SmallVectorImpl<VariableGEPIndex> &Dest,
|
|
const SmallVectorImpl<VariableGEPIndex> &Src) {
|
|
if (Src.empty())
|
|
return;
|
|
|
|
for (unsigned i = 0, e = Src.size(); i != e; ++i) {
|
|
const Value *V = Src[i].V;
|
|
ExtensionKind Extension = Src[i].Extension;
|
|
int64_t Scale = Src[i].Scale;
|
|
|
|
// Find V in Dest. This is N^2, but pointer indices almost never have more
|
|
// than a few variable indexes.
|
|
for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
|
|
if (!isValueEqualInPotentialCycles(Dest[j].V, V) ||
|
|
Dest[j].Extension != Extension)
|
|
continue;
|
|
|
|
// If we found it, subtract off Scale V's from the entry in Dest. If it
|
|
// goes to zero, remove the entry.
|
|
if (Dest[j].Scale != Scale)
|
|
Dest[j].Scale -= Scale;
|
|
else
|
|
Dest.erase(Dest.begin() + j);
|
|
Scale = 0;
|
|
break;
|
|
}
|
|
|
|
// If we didn't consume this entry, add it to the end of the Dest list.
|
|
if (Scale) {
|
|
VariableGEPIndex Entry = { V, Extension, -Scale };
|
|
Dest.push_back(Entry);
|
|
}
|
|
}
|
|
}
|