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Teach InstCombine to fold "(shr exact X, Y) == 0" --> X == 0, fixing #1 from

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PR9343.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126643 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2011-02-28 08:31:40 +00:00
parent 3dfd98744c
commit b042f8e969
2 changed files with 30 additions and 5 deletions
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18
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1289,13 +1289,21 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
}
case Instruction::LShr: // (icmp pred (shr X, ShAmt), CI)
case Instruction::AShr:
// Only handle equality comparisons of shift-by-constant.
if (ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1)))
if (Instruction *Res = FoldICmpShrCst(ICI, cast<BinaryOperator>(LHSI),
ShAmt))
case Instruction::AShr: {
// Handle equality comparisons of shift-by-constant.
BinaryOperator *BO = cast<BinaryOperator>(LHSI);
if (ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1))) {
if (Instruction *Res = FoldICmpShrCst(ICI, BO, ShAmt))
return Res;
}
// Handle exact shr's.
if (ICI.isEquality() && BO->isExact() && BO->hasOneUse()) {
if (RHSV.isMinValue())
return new ICmpInst(ICI.getPredicate(), BO->getOperand(0), RHS);
}
break;
}
case Instruction::SDiv:
case Instruction::UDiv:

17
test/Transforms/InstCombine/icmp.ll
View File

@ -387,3 +387,20 @@ define i1 @test39(i31 %X, i32 %Y) {
%C = icmp slt i32 %B, 0
ret i1 %C
}
; PR9343 #1
; CHECK: test40
; CHECK %B = icmp eq i32 %X, 0
define i1 @test40(i32 %X, i32 %Y) {
%A = ashr exact i32 %X, %Y
%B = icmp eq i32 %A, 0
ret i1 %B
}
; CHECK: test41
; CHECK %B = icmp ne i32 %X, 0
define i1 @test41(i32 %X, i32 %Y) {
%A = lshr exact i32 %X, %Y
%B = icmp ne i32 %A, 0
ret i1 %B
}