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Optimize (x/C)*C to x if the division is exact.

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llvm-svn: 78811
This commit is contained in:
Dan Gohman 2009-08-12 16:33:09 +00:00
parent 9ea1b2644b
commit d5b6e35080
2 changed files with 47 additions and 1 deletions
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11
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -2701,6 +2701,15 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
BO->getOpcode() == Instruction::SDiv)) {
Value *Op0BO = BO->getOperand(0), *Op1BO = BO->getOperand(1);
// If the division is exact, X % Y is zero.
if (SDivOperator *SDiv = dyn_cast<SDivOperator>(BO))
if (SDiv->isExact()) {
if (Op1BO == Op1)
return ReplaceInstUsesWith(I, Op0BO);
else
return BinaryOperator::CreateNeg(Op0BO);
}
Instruction *Rem;
if (BO->getOpcode() == Instruction::UDiv)
Rem = BinaryOperator::CreateURem(Op0BO, Op1BO);
@ -3060,7 +3069,7 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
if (RHS->isAllOnesValue())
return BinaryOperator::CreateNeg(Op0);
// sdiv X, C --> ashr X, log2(C)
// sdiv X, C --> ashr X, log2(C)
if (cast<SDivOperator>(&I)->isExact() &&
RHS->getValue().isNonNegative() &&
RHS->getValue().isPowerOf2()) {

37
test/Transforms/InstCombine/exact-sdiv.ll
View File

@ -13,3 +13,40 @@ define i32 @bar(i32 %x) {
%y = sdiv exact i32 %x, 8
ret i32 %y
}
; CHECK: i32 @a0
; CHECK: %y = srem i32 %x, 3
; CHECK: %z = sub i32 %x, %y
; CHECK: ret i32 %z
define i32 @a0(i32 %x) {
%y = sdiv i32 %x, 3
%z = mul i32 %y, 3
ret i32 %z
}
; CHECK: i32 @b0
; CHECK: ret i32 %x
define i32 @b0(i32 %x) {
%y = sdiv exact i32 %x, 3
%z = mul i32 %y, 3
ret i32 %z
}
; CHECK: i32 @a1
; CHECK: %y = srem i32 %x, 3
; CHECK: %z = sub i32 %y, %x
; CHECK: ret i32 %z
define i32 @a1(i32 %x) {
%y = sdiv i32 %x, 3
%z = mul i32 %y, -3
ret i32 %z
}
; CHECK: i32 @b1
; CHECK: %z = sub i32 0, %x
; CHECK: ret i32 %z
define i32 @b1(i32 %x) {
%y = sdiv exact i32 %x, 3
%z = mul i32 %y, -3
ret i32 %z
}