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Clean up: Refactoring the hardcoded value of 6 for FindAvailableLoadedValue()'s parameter MaxInstsToScan. (Complete version of r247497. See D12886)

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248022 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Larisse Voufo 2015-09-18 19:14:35 +00:00
parent dc18fbbb2d
commit 69328805da
5 changed files with 31 additions and 11 deletions
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11
include/llvm/Analysis/Loads.h
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@ -16,6 +16,7 @@
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/Support/CommandLine.h"
namespace llvm {
@ -29,15 +30,19 @@ class MDNode;
bool isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
unsigned Align);
/// DefMaxInstsToScan - the default number of maximum instructions
/// to scan in the block, used by FindAvailableLoadedValue().
extern cl::opt<unsigned> DefMaxInstsToScan;
/// FindAvailableLoadedValue - Scan the ScanBB block backwards (starting at
/// the instruction before ScanFrom) checking to see if we have the value at
/// the memory address *Ptr locally available within a small number of
/// instructions. If the value is available, return it.
///
/// If not, return the iterator for the last validated instruction that the
/// If not, return the iterator for the last validated instruction that the
/// value would be live through. If we scanned the entire block and didn't
/// find something that invalidates *Ptr or provides it, ScanFrom would be
/// left at begin() and this returns null. ScanFrom could also be left
/// left at begin() and this returns null. ScanFrom could also be left
///
/// MaxInstsToScan specifies the maximum instructions to scan in the block.
/// If it is set to 0, it will scan the whole block. You can also optionally
@ -48,7 +53,7 @@ bool isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
/// is found, it is left unmodified.
Value *FindAvailableLoadedValue(Value *Ptr, BasicBlock *ScanBB,
BasicBlock::iterator &ScanFrom,
unsigned MaxInstsToScan = 6,
unsigned MaxInstsToScan = DefMaxInstsToScan,
AliasAnalysis *AA = nullptr,
AAMDNodes *AATags = nullptr);

5
lib/Analysis/Lint.cpp
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@ -829,8 +829,9 @@ Value *Lint::findValueImpl(Value *V, bool OffsetOk,
for (;;) {
if (!VisitedBlocks.insert(BB).second)
break;
if (Value *U = FindAvailableLoadedValue(L->getPointerOperand(),
BB, BBI, 6, AA))
if (Value *U =
FindAvailableLoadedValue(L->getPointerOperand(),
BB, BBI, DefMaxInstsToScan, AA))
return findValueImpl(U, OffsetOk, Visited);
if (BBI != BB->begin()) break;
BB = BB->getUniquePredecessor();

12
lib/Analysis/Loads.cpp
View File

@ -161,6 +161,18 @@ bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom,
return false;
}
/// DefMaxInstsToScan - the default number of maximum instructions
/// to scan in the block, used by FindAvailableLoadedValue().
/// FindAvailableLoadedValue() was introduced in r60148, to improve jump
/// threading in part by eliminating partially redundant loads.
/// At that point, the value of MaxInstsToScan was already set to '6'
/// without documented explanation.
cl::opt<unsigned>
llvm::DefMaxInstsToScan("available-load-scan-limit", cl::init(6), cl::Hidden,
cl::desc("Use this to specify the default maximum number of instructions "
"to scan backward from a given instruction, when searching for "
"available loaded value"));
/// \brief Scan the ScanBB block backwards to see if we have the value at the
/// memory address *Ptr locally available within a small number of instructions.
///

7
lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
View File

@ -750,8 +750,9 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
// separated by a few arithmetic operations.
BasicBlock::iterator BBI = &LI;
AAMDNodes AATags;
if (Value *AvailableVal = FindAvailableLoadedValue(Op, LI.getParent(), BBI,
6, AA, &AATags)) {
if (Value *AvailableVal =
FindAvailableLoadedValue(Op, LI.getParent(), BBI,
DefMaxInstsToScan, AA, &AATags)) {
if (LoadInst *NLI = dyn_cast<LoadInst>(AvailableVal)) {
unsigned KnownIDs[] = {
LLVMContext::MD_tbaa,
@ -822,7 +823,7 @@ Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
}
// load (select (cond, null, P)) -> load P
if (isa<ConstantPointerNull>(SI->getOperand(1)) &&
if (isa<ConstantPointerNull>(SI->getOperand(1)) &&
LI.getPointerAddressSpace() == 0) {
LI.setOperand(0, SI->getOperand(2));
return &LI;

7
lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -769,7 +769,7 @@ bool JumpThreading::ProcessBlock(BasicBlock *BB) {
// If we're branching on a conditional, LVI might be able to determine
// it's value at the branch instruction. We only handle comparisons
// against a constant at this time.
// TODO: This should be extended to handle switches as well.
// TODO: This should be extended to handle switches as well.
BranchInst *CondBr = dyn_cast<BranchInst>(BB->getTerminator());
Constant *CondConst = dyn_cast<Constant>(CondCmp->getOperand(1));
if (CondBr && CondConst && CondBr->isConditional()) {
@ -877,7 +877,7 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
BasicBlock::iterator BBIt = LI;
if (Value *AvailableVal =
FindAvailableLoadedValue(LoadedPtr, LoadBB, BBIt, 6)) {
FindAvailableLoadedValue(LoadedPtr, LoadBB, BBIt, DefMaxInstsToScan)) {
// If the value of the load is locally available within the block, just use
// it. This frequently occurs for reg2mem'd allocas.
//cerr << "LOAD ELIMINATED:\n" << *BBIt << *LI << "\n";
@ -922,7 +922,8 @@ bool JumpThreading::SimplifyPartiallyRedundantLoad(LoadInst *LI) {
// Scan the predecessor to see if the value is available in the pred.
BBIt = PredBB->end();
AAMDNodes ThisAATags;
Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt, 6,
Value *PredAvailable = FindAvailableLoadedValue(LoadedPtr, PredBB, BBIt,
DefMaxInstsToScan,
nullptr, &ThisAATags);
if (!PredAvailable) {
OneUnavailablePred = PredBB;