[llvm] r274926 - [InstCombine] don't form select from logic ops if it's unlikely that we'll eliminate any ops
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Fri Jul 8 13:53:29 PDT 2016
Author: spatel
Date: Fri Jul 8 15:53:29 2016
New Revision: 274926
URL: http://llvm.org/viewvc/llvm-project?rev=274926&view=rev
Log:
[InstCombine] don't form select from logic ops if it's unlikely that we'll eliminate any ops
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
llvm/trunk/test/Transforms/InstCombine/logical-select.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp?rev=274926&r1=274925&r2=274926&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Fri Jul 8 15:53:29 2016
@@ -2222,23 +2222,28 @@ Instruction *InstCombiner::visitOr(Binar
}
}
- // (Cond & C) | (~Cond & D) -> Cond ? C : D, and commuted variants.
- if (Value *V = matchSelectFromAndOr(A, C, B, D, *Builder))
- return replaceInstUsesWith(I, V);
- if (Value *V = matchSelectFromAndOr(A, C, D, B, *Builder))
- return replaceInstUsesWith(I, V);
- if (Value *V = matchSelectFromAndOr(C, A, B, D, *Builder))
- return replaceInstUsesWith(I, V);
- if (Value *V = matchSelectFromAndOr(C, A, D, B, *Builder))
- return replaceInstUsesWith(I, V);
- if (Value *V = matchSelectFromAndOr(B, D, A, C, *Builder))
- return replaceInstUsesWith(I, V);
- if (Value *V = matchSelectFromAndOr(B, D, C, A, *Builder))
- return replaceInstUsesWith(I, V);
- if (Value *V = matchSelectFromAndOr(D, B, A, C, *Builder))
- return replaceInstUsesWith(I, V);
- if (Value *V = matchSelectFromAndOr(D, B, C, A, *Builder))
- return replaceInstUsesWith(I, V);
+ // Don't try to form a select if it's unlikely that we'll get rid of at
+ // least one of the operands. A select is generally more expensive than the
+ // 'or' that it is replacing.
+ if (Op0->hasOneUse() || Op1->hasOneUse()) {
+ // (Cond & C) | (~Cond & D) -> Cond ? C : D, and commuted variants.
+ if (Value *V = matchSelectFromAndOr(A, C, B, D, *Builder))
+ return replaceInstUsesWith(I, V);
+ if (Value *V = matchSelectFromAndOr(A, C, D, B, *Builder))
+ return replaceInstUsesWith(I, V);
+ if (Value *V = matchSelectFromAndOr(C, A, B, D, *Builder))
+ return replaceInstUsesWith(I, V);
+ if (Value *V = matchSelectFromAndOr(C, A, D, B, *Builder))
+ return replaceInstUsesWith(I, V);
+ if (Value *V = matchSelectFromAndOr(B, D, A, C, *Builder))
+ return replaceInstUsesWith(I, V);
+ if (Value *V = matchSelectFromAndOr(B, D, C, A, *Builder))
+ return replaceInstUsesWith(I, V);
+ if (Value *V = matchSelectFromAndOr(D, B, A, C, *Builder))
+ return replaceInstUsesWith(I, V);
+ if (Value *V = matchSelectFromAndOr(D, B, C, A, *Builder))
+ return replaceInstUsesWith(I, V);
+ }
// ((A&~B)|(~A&B)) -> A^B
if ((match(C, m_Not(m_Specific(D))) &&
Modified: llvm/trunk/test/Transforms/InstCombine/logical-select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/logical-select.ll?rev=274926&r1=274925&r2=274926&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/logical-select.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/logical-select.ll Fri Jul 8 15:53:29 2016
@@ -300,10 +300,8 @@ define i1 @bools_multi_uses2(i1 %a, i1 %
; CHECK-NEXT: [[NOT:%.*]] = xor i1 %c, true
; CHECK-NEXT: [[AND1:%.*]] = and i1 [[NOT]], %a
; CHECK-NEXT: [[AND2:%.*]] = and i1 %c, %b
-; CHECK-NEXT: [[TMP1:%.*]] = select i1 %c, i1 %b, i1 %a
; CHECK-NEXT: [[ADD:%.*]] = xor i1 [[AND1]], [[AND2]]
-; CHECK-NEXT: [[AND3:%.*]] = and i1 [[TMP1]], [[ADD]]
-; CHECK-NEXT: ret i1 [[AND3]]
+; CHECK-NEXT: ret i1 [[ADD]]
;
%not = xor i1 %c, -1
%and1 = and i1 %not, %a
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