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ConstantFold: div undef, 0 should fold to undef, not zero

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Dividing by zero yields an undefined value.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223924 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2014-12-10 09:14:55 +00:00
parent 6578f1beb1
commit 895316336e
2 changed files with 26 additions and 9 deletions
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28
lib/IR/ConstantFold.cpp
View File

@ -27,12 +27,14 @@
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ManagedStatic.h"
#include "llvm/Support/MathExtras.h"
#include <limits>
using namespace llvm;
using namespace llvm::PatternMatch;
//===----------------------------------------------------------------------===//
// ConstantFold*Instruction Implementations
@ -923,19 +925,27 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
// X * undef -> 0 otherwise
return Constant::getNullValue(C1->getType());
}
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::UDiv:
// X / undef -> undef
if (match(C1, m_Zero()))
return C2;
// undef / 0 -> undef
// undef / 1 -> undef
if (Opcode == Instruction::UDiv || Opcode == Instruction::SDiv)
if (ConstantInt *CI2 = dyn_cast<ConstantInt>(C2))
if (CI2->isOne())
return C1;
// FALL THROUGH
if (match(C2, m_Zero()) || match(C2, m_One()))
return C1;
// undef / X -> 0 otherwise
return Constant::getNullValue(C1->getType());
case Instruction::URem:
case Instruction::SRem:
if (!isa<UndefValue>(C2)) // undef / X -> 0
return Constant::getNullValue(C1->getType());
return C2; // X / undef -> undef
// X % undef -> undef
if (match(C2, m_Undef()))
return C2;
// undef % 0 -> undef
if (match(C2, m_Zero()))
return C1;
// undef % X -> 0 otherwise
return Constant::getNullValue(C1->getType());
case Instruction::Or: // X | undef -> -1
if (isa<UndefValue>(C1) && isa<UndefValue>(C2)) // undef | undef -> undef
return C1;

7
test/Transforms/InstSimplify/undef.ll
View File

@ -188,3 +188,10 @@ define i32 @test23(i32 %a) {
%b = lshr exact i32 undef, %a
ret i32 %b
}
; CHECK-LABEL: @test24
; CHECK: ret i32 undef
define i32 @test24(i32 %a) {
%b = udiv i32 undef, 0
ret i32 %b
}