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ConstantFold: Shifting undef by zero results in undef 

llvm-svn: 224553
This commit is contained in:
David Majnemer 2014-12-18 23:54:43 +00:00
parent 174476ed96
commit 824e011ad7
2 changed files with 30 additions and 0 deletions
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9
llvm/lib/IR/ConstantFold.cpp
View File

@ -956,12 +956,18 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
// X >>l undef -> undef
if (isa<UndefValue>(C2))
return C2;
// undef >>l 0 -> undef
if (match(C2, m_Zero()))
return C1;
// undef >>l X -> 0
return Constant::getNullValue(C1->getType());
case Instruction::AShr:
// X >>a undef -> undef
if (isa<UndefValue>(C2))
return C2;
// undef >>a 0 -> undef
if (match(C2, m_Zero()))
return C1;
// TODO: undef >>a X -> undef if the shift is exact
// undef >>a X -> 0
return Constant::getNullValue(C1->getType());
@ -969,6 +975,9 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
// X << undef -> undef
if (isa<UndefValue>(C2))
return C2;
// undef << 0 -> undef
if (match(C2, m_Zero()))
return C1;
// undef << X -> 0
return Constant::getNullValue(C1->getType());
}

21
llvm/test/Transforms/InstSimplify/undef.ll
View File

@ -244,3 +244,24 @@ define i32 @test31(i32 %a) {
%b = shl i32 undef, %a
ret i32 %b
}
; CHECK-LABEL: @test32
; CHECK: ret i32 undef
define i32 @test32(i32 %a) {
%b = shl i32 undef, 0
ret i32 %b
}
; CHECK-LABEL: @test33
; CHECK: ret i32 undef
define i32 @test33(i32 %a) {
%b = ashr i32 undef, 0
ret i32 %b
}
; CHECK-LABEL: @test34
; CHECK: ret i32 undef
define i32 @test34(i32 %a) {
%b = lshr i32 undef, 0
ret i32 %b
}