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ConstantFold: an undef shift amount results in undef 

X shifted by undef results in undef because the undef value can
represent values greater than the width of the operands.

llvm-svn: 223968
This commit is contained in:
David Majnemer 2014-12-10 21:38:05 +00:00
parent db0b13cef0
commit 89cf6d79eb
2 changed files with 35 additions and 13 deletions
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27
llvm/lib/IR/ConstantFold.cpp
View File

@ -951,21 +951,22 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
return C1;
return Constant::getAllOnesValue(C1->getType()); // undef | X -> ~0
case Instruction::LShr:
if (isa<UndefValue>(C2) && isa<UndefValue>(C1))
return C1; // undef lshr undef -> undef
return Constant::getNullValue(C1->getType()); // X lshr undef -> 0
// undef lshr X -> 0
// X >>l undef -> undef
if (isa<UndefValue>(C2))
return C2;
// undef >>l X -> 0
return Constant::getNullValue(C1->getType());
case Instruction::AShr:
if (!isa<UndefValue>(C2)) // undef ashr X --> all ones
return Constant::getAllOnesValue(C1->getType());
else if (isa<UndefValue>(C1))
return C1; // undef ashr undef -> undef
else
return C1; // X ashr undef --> X
// X >>a undef -> undef
if (isa<UndefValue>(C2))
return C2;
// undef >>a X -> all ones
return Constant::getAllOnesValue(C1->getType());
case Instruction::Shl:
if (isa<UndefValue>(C2) && isa<UndefValue>(C1))
return C1; // undef shl undef -> undef
// undef << X -> 0 or X << undef -> 0
// X << undef -> undef
if (isa<UndefValue>(C2))
return C2;
// undef << X -> 0
return Constant::getNullValue(C1->getType());
}
}

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

@ -195,3 +195,24 @@ define i32 @test24(i32 %a) {
%b = udiv i32 undef, 0
ret i32 %b
}
; CHECK-LABEL: @test25
; CHECK: ret i32 undef
define i32 @test25(i32 %a) {
%b = lshr i32 0, undef
ret i32 %b
}
; CHECK-LABEL: @test26
; CHECK: ret i32 undef
define i32 @test26(i32 %a) {
%b = ashr i32 0, undef
ret i32 %b
}
; CHECK-LABEL: @test27
; CHECK: ret i32 undef
define i32 @test27(i32 %a) {
%b = shl i32 0, undef
ret i32 %b
}