Revert r1296656, "Fix rdar://9289512 - not folding load into compare at -O0...",
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
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index af31888..25dd97d 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -746,31 +746,9 @@
-/// 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 @@
/// 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 @@
// 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;
}