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Chris prefers icmp/select over udiv!

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60187 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2008-11-27 22:41:10 +00:00
parent df563ca1f3
commit 8ca5248522
3 changed files with 19 additions and 10 deletions
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14
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -2882,13 +2882,21 @@ Instruction *InstCombiner::visitUDiv(BinaryOperator &I) {
if (Instruction *Common = commonIDivTransforms(I))
return Common;
// X udiv C^2 -> X >> C
// Check to see if this is an unsigned division with an exact power of 2,
// if so, convert to a right shift.
if (ConstantInt *C = dyn_cast<ConstantInt>(Op1)) {
// X udiv C^2 -> X >> C
// Check to see if this is an unsigned division with an exact power of 2,
// if so, convert to a right shift.
if (C->getValue().isPowerOf2()) // 0 not included in isPowerOf2
return BinaryOperator::CreateLShr(Op0,
ConstantInt::get(Op0->getType(), C->getValue().logBase2()));
// X udiv C, where C >= signbit
if (C->getValue().isNegative()) {
Value *IC = InsertNewInstBefore(new ICmpInst(ICmpInst::ICMP_ULT, Op0, C),
I);
return SelectInst::Create(IC, Constant::getNullValue(I.getType()),
ConstantInt::get(I.getType(), 1));
}
}
// X udiv (C1 << N), where C1 is "1<<C2" --> X >> (N+C2)

6
test/Transforms/InstCombine/2008-11-27-UDivNegative.ll Normal file
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@ -0,0 +1,6 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep div
define i8 @test(i8 %x) readnone nounwind {
%A = udiv i8 %x, 250
ret i8 %A
}

9
test/Transforms/InstCombine/udiv-simplify-bug-1.ll
View File

@ -1,16 +1,11 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis > %t1.ll
; RUN: grep udiv %t1.ll | count 3
; RUN: grep zext %t1.ll | count 3
; RUN: grep udiv %t1.ll | count 2
; RUN: grep zext %t1.ll | count 2
; PR2274
; The udiv instructions shouldn't be optimized away, and the
; sext instructions should be optimized to zext.
define i64 @foo(i32 %x) nounwind {
%r = udiv i32 %x, -1
%z = sext i32 %r to i64
ret i64 %z
}
define i64 @bar(i32 %x) nounwind {
%y = lshr i32 %x, 30
%r = udiv i32 %y, 3