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InstCombine, InstSimplify: (%X /s C1) /s C2 isn't always 0 when C1 * C2 overflow

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consider:
C1 = INT_MIN
C2 = -1

C1 * C2 overflows without a doubt but consider the following:
%x = i32 INT_MIN

This means that (%X /s C1) is 1 and (%X /s C1) /s C2 is -1.

N. B.  Move the unsigned version of this transform to InstSimplify, it
doesn't create any new instructions.

This fixes PR21243.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219567 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2014-10-11 10:20:01 +00:00
parent 2af441e26e
commit 9043f74acb
4 changed files with 30 additions and 19 deletions
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10
lib/Analysis/InstructionSimplify.cpp
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@ -1057,6 +1057,16 @@ static Value *SimplifyDiv(Instruction::BinaryOps Opcode, Value *Op0, Value *Op1,
(!isSigned && match(Op0, m_URem(m_Value(), m_Specific(Op1)))))
return Constant::getNullValue(Op0->getType());
// (X /u C1) /u C2 -> 0 if C1 * C2 overflow
ConstantInt *C1, *C2;
if (!isSigned && match(Op0, m_UDiv(m_Value(X), m_ConstantInt(C1))) &&
match(Op1, m_ConstantInt(C2))) {
bool Overflow;
C1->getValue().umul_ov(C2->getValue(), Overflow);
if (Overflow)
return Constant::getNullValue(Op0->getType());
}
// If the operation is with the result of a select instruction, check whether
// operating on either branch of the select always yields the same value.
if (isa<SelectInst>(Op0) || isa<SelectInst>(Op1))