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Optimize exact sdiv by a constant power of 2 to ashr. 

llvm-svn: 78714
This commit is contained in:
Dan Gohman 2009-08-11 20:47:47 +00:00
parent 9f94459d24
commit dbae4db67a
2 changed files with 24 additions and 0 deletions
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9
llvm/lib/Transforms/Scalar/InstructionCombining.cpp
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@ -3064,6 +3064,15 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
// sdiv X, -1 == -X // sdiv X, -1 == -X
if (RHS->isAllOnesValue()) if (RHS->isAllOnesValue())
return BinaryOperator::CreateNeg(*Context, Op0); return BinaryOperator::CreateNeg(*Context, Op0);
// sdiv X, C --> ashr X, log2(C)
if (cast<SDivOperator>(&I)->isExact() &&
RHS->getValue().isNonNegative() &&
RHS->getValue().isPowerOf2()) {
Value *ShAmt = llvm::ConstantInt::get(RHS->getType(),
RHS->getValue().exactLogBase2());
return BinaryOperator::CreateAShr(Op0, ShAmt, I.getName());
}
} }
// If the sign bits of both operands are zero (i.e. we can prove they are // If the sign bits of both operands are zero (i.e. we can prove they are

15
llvm/test/Transforms/InstCombine/exact-sdiv.ll Normal file
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@ -0,0 +1,15 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | FileCheck %s
; CHECK: define i32 @foo
; CHECK: sdiv i32 %x, 8
define i32 @foo(i32 %x) {
%y = sdiv i32 %x, 8
ret i32 %y
}
; CHECK: define i32 @bar
; CHECK: ashr i32 %x, 3
define i32 @bar(i32 %x) {
%y = sdiv exact i32 %x, 8
ret i32 %y
}