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InstCombine: Propagate exact for (sdiv X, Pow2) -> (udiv X, Pow2) 

llvm-svn: 222625
This commit is contained in:
David Majnemer 2014-11-22 20:00:41 +00:00
parent ec6e481bc5
commit fb3805576b
2 changed files with 15 additions and 2 deletions
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6
llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@ -1102,12 +1102,14 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
return BO;
}
if (match(Op1, m_Shl(m_Power2(), m_Value()))) {
if (isKnownToBeAPowerOfTwo(Op1, /*OrZero*/true, 0, AT, &I, DT)) {
// 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());
auto *BO = BinaryOperator::CreateUDiv(Op0, Op1, I.getName());
BO->setIsExact(I.isExact());
return BO;
}
}
}

11
llvm/test/Transforms/InstCombine/div.ll
View File

@ -314,3 +314,14 @@ define i32 @test35(i32 %A) {
; CHECK-NEXT: %[[udiv:.*]] = udiv exact i32 %[[and]], 2147483647
; CHECK-NEXT: ret i32 %[[udiv]]
}
define i32 @test36(i32 %A) {
%and = and i32 %A, 2147483647
%shl = shl nsw i32 1, %A
%mul = sdiv exact i32 %and, %shl
ret i32 %mul
; CHECK-LABEL: @test36(
; CHECK-NEXT: %[[and:.*]] = and i32 %A, 2147483647
; CHECK-NEXT: %[[shr:.*]] = lshr exact i32 %[[and]], %A
; CHECK-NEXT: ret i32 %[[shr]]
}