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Add combine: X sdiv (1 << Y) -> X udiv (1 << Y) when X doesn't have the

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sign bit set.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76304 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman 2009-07-18 09:53:21 +00:00
parent 191a0aee4f
commit 8be17397c0
2 changed files with 24 additions and 4 deletions
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13
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -3104,10 +3104,21 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
// unsigned inputs), turn this into a udiv.
if (I.getType()->isInteger()) {
APInt Mask(APInt::getSignBit(I.getType()->getPrimitiveSizeInBits()));
if (MaskedValueIsZero(Op1, Mask) && MaskedValueIsZero(Op0, Mask)) {
if (MaskedValueIsZero(Op0, Mask)) {
if (MaskedValueIsZero(Op1, Mask)) {
// X sdiv Y -> X udiv Y, iff X and Y don't have sign bit set
return BinaryOperator::CreateUDiv(Op0, Op1, I.getName());
}
ConstantInt *ShiftedInt;
if (match(Op1, m_Shl(m_ConstantInt(ShiftedInt), m_Value()), *Context) &&
ShiftedInt->getValue().isPowerOf2()) {
// X sdiv (1 << Y) -> X udiv (1 << Y) ( -> X u>> Y)
// Safe because the only negative value (1 << Y) can take on is
// INT_MIN, and X sdiv INT_MIN == X udiv INT_MIN == 0 if X doesn't have
// the sign bit set.
return BinaryOperator::CreateUDiv(Op0, Op1, I.getName());
}
}
}
return 0;

9
test/Transforms/InstCombine/sdiv-shift.ll Normal file
View File

@ -0,0 +1,9 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep div
define i32 @a(i16 zeroext %x, i32 %y) nounwind {
entry:
%conv = zext i16 %x to i32
%s = shl i32 2, %y
%d = sdiv i32 %conv, %s
ret i32 %d
}