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[BasicAA] NFC - utility function for two's complement wrap-around

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@259290 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Gerolf Hoflehner 2016-01-30 02:42:11 +00:00
parent 958f45c5b1
commit f6d75eeed4
1 changed files with 15 additions and 7 deletions
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22
lib/Analysis/BasicAliasAnalysis.cpp
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@ -37,16 +37,17 @@
#include "llvm/Pass.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
#define DEBUG_TYPE "basicaa"
using namespace llvm;
/// Enable analysis of recursive PHI nodes.
static cl::opt<bool> EnableRecPhiAnalysis("basicaa-recphi", cl::Hidden,
cl::init(false));
/// SearchLimitReached / SearchTimes shows how often the limit of
/// to decompose GEPs is reached. It will affect the precision
/// of basic alias analysis.
#define DEBUG_TYPE "basicaa"
STATISTIC(SearchLimitReached, "Number of times the limit to "
"decompose GEPs is reached");
STATISTIC(SearchTimes, "Number of times a GEP is decomposed");
@ -319,6 +320,16 @@ static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL,
return V;
}
/// To ensure a pointer offset fits in an integer of size PointerSize
/// (in bits) when that size is smaller than 64. This is an issue in
/// particular for 32b programs with negative indices that rely on two's
/// complement wrap-arounds for correct alias information.
static int64_t adjustToPointerSize(int64_t Offset, unsigned PointerSize) {
assert(PointerSize <= 64 && "Invalid PointerSize!");
unsigned ShiftBits = 64 - PointerSize;
return (uint64_t)Offset << ShiftBits >> ShiftBits;
}
/// If V is a symbolic pointer expression, decompose it into a base pointer
/// with a constant offset and a number of scaled symbolic offsets.
///
@ -387,6 +398,7 @@ static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL,
unsigned AS = GEPOp->getPointerAddressSpace();
// Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
gep_type_iterator GTI = gep_type_begin(GEPOp);
unsigned PointerSize = DL.getPointerSizeInBits(AS);
for (User::const_op_iterator I = GEPOp->op_begin() + 1, E = GEPOp->op_end();
I != E; ++I) {
const Value *Index = *I;
@ -415,7 +427,6 @@ static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL,
// If the integer type is smaller than the pointer size, it is implicitly
// sign extended to pointer size.
unsigned Width = Index->getType()->getIntegerBitWidth();
unsigned PointerSize = DL.getPointerSizeInBits(AS);
if (PointerSize > Width)
SExtBits += PointerSize - Width;
@ -445,10 +456,7 @@ static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL,
// Make sure that we have a scale that makes sense for this target's
// pointer size.
if (unsigned ShiftBits = 64 - PointerSize) {
Scale <<= ShiftBits;
Scale = (int64_t)Scale >> ShiftBits;
}
Scale = adjustToPointerSize(Scale, PointerSize);
if (Scale) {
VariableGEPIndex Entry = {Index, ZExtBits, SExtBits,