[llvm] r296129 - [InstCombine] don't try SimplifyDemandedInstructionBits from zext/sext because it's slow and unnecessary
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Fri Feb 24 07:18:42 PST 2017
Author: spatel
Date: Fri Feb 24 09:18:42 2017
New Revision: 296129
URL: http://llvm.org/viewvc/llvm-project?rev=296129&view=rev
Log:
[InstCombine] don't try SimplifyDemandedInstructionBits from zext/sext because it's slow and unnecessary
This one seems more obvious than D30270 that it can't make improvements because an extension always needs
all of the incoming bits. There's one specific transform in SimplifyDemandedInstructionBits of converting
a sext to a zext when the sign-bit is known zero, but that is handled explicitly in visitSext() with
ComputeSignBit().
Like D30270, there are no IR differences (other than instruction names) for the case in PR32037:
https://bugs.llvm.org//show_bug.cgi?id=32037
...and no regression test differences.
Zext/sext are a smaller part of the profile, but this still appears to shave off another 0.5% or so from
'opt -O2'.
Differential Revision: https://reviews.llvm.org/D30280
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=296129&r1=296128&r2=296129&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Fri Feb 24 09:18:42 2017
@@ -838,11 +838,6 @@ Instruction *InstCombiner::visitZExt(ZEx
if (Instruction *Result = commonCastTransforms(CI))
return Result;
- // See if we can simplify any instructions used by the input whose sole
- // purpose is to compute bits we don't care about.
- if (SimplifyDemandedInstructionBits(CI))
- return &CI;
-
Value *Src = CI.getOperand(0);
Type *SrcTy = Src->getType(), *DestTy = CI.getType();
@@ -1124,11 +1119,6 @@ Instruction *InstCombiner::visitSExt(SEx
if (Instruction *I = commonCastTransforms(CI))
return I;
- // See if we can simplify any instructions used by the input whose sole
- // purpose is to compute bits we don't care about.
- if (SimplifyDemandedInstructionBits(CI))
- return &CI;
-
Value *Src = CI.getOperand(0);
Type *SrcTy = Src->getType(), *DestTy = CI.getType();
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