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Revert r1296656, "Fix rdar://9289512 - not folding load into compare at -O0...",

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which broke a couple GCC test suite tests at -O0.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129914 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Daniel Dunbar
2011-04-21 16:14:46 +00:00
parent 326fb9d1fb
commit 63c21deee1
3 changed files with 16 additions and 65 deletions
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56
lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
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@@ -746,31 +746,9 @@ void SelectionDAGISel::PrepareEHLandingPad() {
/// TryToFoldFastISelLoad - We're checking to see if we can fold the specified
/// load into the specified FoldInst. Note that we could have a sequence where
/// multiple LLVM IR instructions are folded into the same machineinstr. For
/// example we could have:
/// A: x = load i32 *P
/// B: y = icmp A, 42
/// C: br y, ...
///
/// In this scenario, LI is "A", and FoldInst is "C". We know about "B" (and
/// any other folded instructions) because it is between A and C.
///
/// If we succeed in folding the load into the operation, return true.
///
bool SelectionDAGISel::TryToFoldFastISelLoad(const LoadInst *LI,
const Instruction *FoldInst,
FastISel *FastIS) {
SmallPtrSet<const Instruction*, 4> FoldedInsts;
for (BasicBlock::const_iterator II = FoldInst; &*II != LI; --II)
FoldedInsts.insert(II);
// We know that the load has a single use, but don't know what it is. If it
// isn't one of the folded instructions, then we can't succeed here.
if (!FoldedInsts.count(LI->use_back()))
return false;
// Don't try to fold volatile loads. Target has to deal with alignment
// constraints.
if (LI->isVolatile()) return false;
@@ -855,10 +833,10 @@ static void CheckLineNumbers(const MachineBasicBlock *MBB) {
/// Return false if it needs to be emitted.
static bool isFoldedOrDeadInstruction(const Instruction *I,
FunctionLoweringInfo *FuncInfo) {
return !I->mayWriteToMemory() && // Side-effecting instructions aren't folded.
!isa<TerminatorInst>(I) && // Terminators aren't folded.
!isa<DbgInfoIntrinsic>(I) && // Debug instructions aren't folded.
!FuncInfo->isExportedInst(I); // Exported instrs must be computed.
return !I->mayWriteToMemory() &&
!isa<TerminatorInst>(I) &&
!isa<DbgInfoIntrinsic>(I) &&
!FuncInfo->isExportedInst(I);
}
void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
@@ -950,20 +928,16 @@ void SelectionDAGISel::SelectAllBasicBlocks(const Function &Fn) {
// Try to select the instruction with FastISel.
if (FastIS->SelectInstruction(Inst)) {
// If fast isel succeeded, skip over all the folded instructions, and
// then see if there is a load right before the selected instructions.
// Try to fold the load if so.
const Instruction *BeforeInst = Inst;
while (BeforeInst != Begin) {
BeforeInst = llvm::prior(BasicBlock::const_iterator(BeforeInst));
if (!isFoldedOrDeadInstruction(BeforeInst, FuncInfo))
break;
}
if (BeforeInst != Inst && isa<LoadInst>(BeforeInst) &&
BeforeInst->hasOneUse() &&
TryToFoldFastISelLoad(cast<LoadInst>(BeforeInst), Inst, FastIS))
// If we succeeded, don't re-select the load.
BI = llvm::next(BasicBlock::const_iterator(BeforeInst));
// If fast isel succeeded, check to see if there is a single-use
// non-volatile load right before the selected instruction, and see if
// the load is used by the instruction. If so, try to fold it.
const Instruction *BeforeInst = 0;
if (Inst != Begin)
BeforeInst = llvm::prior(llvm::prior(BI));
if (BeforeInst && isa<LoadInst>(BeforeInst) &&
BeforeInst->hasOneUse() && *BeforeInst->use_begin() == Inst &&
TryToFoldFastISelLoad(cast<LoadInst>(BeforeInst), FastIS))
--BI; // If we succeeded, don't re-select the load.
continue;
}