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Revert r56315. When the instruction to speculate is a load, this

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code can incorrectly move the load across a store. This never
happens in practice today, but only because the current
heuristics accidentally preclude it.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147623 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2012-01-05 22:54:35 +00:00
parent 1031111f84
commit dd35df15a2
2 changed files with 3 additions and 27 deletions
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28
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -1063,32 +1063,8 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
return false;
}
// If we get here, we can hoist the instruction. Try to place it
// before the icmp instruction preceding the conditional branch.
BasicBlock::iterator InsertPos = BI;
if (InsertPos != BIParent->begin())
--InsertPos;
// Skip debug info between condition and branch.
while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
--InsertPos;
if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
SmallPtrSet<Instruction *, 4> BB1Insns;
for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
BB1I != BB1E; ++BB1I)
BB1Insns.insert(BB1I);
for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
UI != UE; ++UI) {
Instruction *Use = cast<Instruction>(*UI);
if (!BB1Insns.count(Use)) continue;
// If BrCond uses the instruction that place it just before
// branch instruction.
InsertPos = BI;
break;
}
} else
InsertPos = BI;
BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
// If we get here, we can hoist the instruction.
BIParent->getInstList().splice(BI, BB1->getInstList(), HInst);
// Create a select whose true value is the speculatively executed value and
// false value is the previously determined FalseV.

2
test/Transforms/SimplifyCFG/SpeculativeExec.ll
View File

@ -13,8 +13,8 @@ bb1: ; preds = %entry
%tmp2 = icmp sgt i32 %c, 1
br i1 %tmp2, label %bb2, label %bb3
; CHECK: bb1:
; CHECK-NEXT: add i32 %a, 1
; CHECK-NEXT: icmp sgt i32 %c, 1
; CHECK-NEXT: add i32 %a, 1
; CHECK-NEXT: select i1 %tmp2, i32 %tmp3, i32 %a
; CHECK-NEXT: br label %bb3