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Revert r173342 temporarily. It appears to cause a very late miscompile

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of stage2 in a bootstrap. Still investigating....

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173343 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth 2013-01-24 13:24:24 +00:00
parent 1f255419d4
commit eacef325c6
2 changed files with 9 additions and 47 deletions
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27
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -1369,8 +1369,7 @@ static bool SinkThenElseCodeToEnd(BranchInst *BI1) {
/// \endcode
///
/// \returns true if the conditional block is removed.
static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
const TargetTransformInfo &TTI) {
static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB) {
// Be conservative for now. FP select instruction can often be expensive.
Value *BrCond = BI->getCondition();
if (isa<FCmpInst>(BrCond))
@ -1399,22 +1398,15 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
// Only speculatively execution a single instruction (not counting the
// terminator) for now.
SpeculationCost += TTI.getUserCost(I);
if (SpeculationCost > TargetTransformInfo::TCC_Basic)
++SpeculationCost;
if (SpeculationCost > 1)
return false;
// Don't hoist the instruction if it's unsafe or expensive.
if (!isSafeToSpeculativelyExecute(I))
return false;
// FIXME: This should really be a cost metric, but our cost model doesn't
// accurately model the expense of select.
if (isa<SelectInst>(I))
if (ComputeSpeculationCost(I) > PHINodeFoldingThreshold)
return false;
// FIXME: The cost metric currently doesn't reason accurately about simple
// versus complex GEPs, take a conservative approach here.
if (GEPOperator *GEP = dyn_cast<GEPOperator>(I))
if (!GEP->hasAllConstantIndices())
return false;
// Do not hoist the instruction if any of its operands are defined but not
// used in this BB. The transformation will prevent the operand from
@ -1457,10 +1449,9 @@ static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *ThenBB,
// Account for the cost of an unfolded ConstantExpr which could end up
// getting expanded into Instructions.
// FIXME: This doesn't account for how many operations are combined in the
// constant expression. The cost functions in TTI don't yet correctly model
// constant expression costs.
SpeculationCost += TargetTransformInfo::TCC_Basic;
if (SpeculationCost > TargetTransformInfo::TCC_Basic)
// constant expression.
++SpeculationCost;
if (SpeculationCost > 1)
return false;
}
@ -3877,7 +3868,7 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
if (Succ0TI->getNumSuccessors() == 1 &&
Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0), TTI))
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
return SimplifyCFG(BB, TTI, TD) | true;
}
} else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
@ -3886,7 +3877,7 @@ bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
if (Succ1TI->getNumSuccessors() == 1 &&
Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1), TTI))
if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
return SimplifyCFG(BB, TTI, TD) | true;
}

29
test/Transforms/SimplifyCFG/SpeculativeExec.ll
View File

@ -108,32 +108,3 @@ end:
ret i8* %x10
}
define i16 @test5(i1* %dummy, i16 %a, i16 %b) {
; Test that we speculate no-op instructions.
; CHECK: @test5
entry:
%cond1 = load volatile i1* %dummy
br i1 %cond1, label %if, label %end
if:
%cond2 = load volatile i1* %dummy
%a.conv = sext i16 %a to i32
%b.conv = sext i16 %b to i32
%cmp = icmp ult i32 %a.conv, %b.conv
br i1 %cond2, label %then, label %end
then:
%sub = sub i32 %a.conv, %b.conv
%sub.conv = trunc i32 %sub to i16
br label %end
end:
%x = phi i16 [ %a, %entry ], [ %b, %if ], [ %sub.conv, %then ]
; CHECK-NOT: phi
; CHECK: select i1
ret i16 %x
}