[llvm] r274932 - [InstCombine] don't form select from bitcasted logic ops if bitcasts have >1 use

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Fri Jul  8 16:17:51 2016
New Revision: 274932

URL: http://llvm.org/viewvc/llvm-project?rev=274932&view=rev
Log:
[InstCombine] don't form select from bitcasted logic ops if bitcasts have >1 use

This isn't a sure thing (are 2 extra bitcasts less expensive than a logic op?), 
but we'll try to err on the conservative side by going with the case that has
less IR instructions.

Note: This question came up in http://reviews.llvm.org/D22114 , but this part is
independent of that patch proposal, so I'm making this small change ahead of that
one. 

See also:
http://reviews.llvm.org/rL274926


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=274932&r1=274931&r2=274932&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp Fri Jul  8 16:17:51 2016
@@ -1619,8 +1619,8 @@ static Value *matchSelectFromAndOr(Value
   // through its bitcast and the corresponding bitcast of the 'not' condition.
   Type *OrigType = A->getType();
   Value *SrcA, *SrcB;
-  if (match(A, m_BitCast(m_Value(SrcA))) &&
-      match(B, m_BitCast(m_Value(SrcB)))) {
+  if (match(A, m_OneUse(m_BitCast(m_Value(SrcA)))) &&
+      match(B, m_OneUse(m_BitCast(m_Value(SrcB))))) {
     A = SrcA;
     B = SrcB;
   }

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=274932&r1=274931&r2=274932&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/logical-select.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/logical-select.ll Fri Jul  8 16:17:51 2016
@@ -265,15 +265,14 @@ define <2 x i64> @bitcast_select_swap7(<
 define <2 x i64> @bitcast_select_multi_uses(<4 x i1> %cmp, <2 x i64> %a, <2 x i64> %b) {
 ; CHECK-LABEL: @bitcast_select_multi_uses(
 ; CHECK-NEXT:    [[SEXT:%.*]] = sext <4 x i1> %cmp to <4 x i32>
+; CHECK-NEXT:    [[BC1:%.*]] = bitcast <4 x i32> [[SEXT]] to <2 x i64>
+; CHECK-NEXT:    [[AND1:%.*]] = and <2 x i64> [[BC1]], %a
 ; CHECK-NEXT:    [[NEG:%.*]] = xor <4 x i32> [[SEXT]], <i32 -1, i32 -1, i32 -1, i32 -1>
 ; CHECK-NEXT:    [[BC2:%.*]] = bitcast <4 x i32> [[NEG]] to <2 x i64>
 ; CHECK-NEXT:    [[AND2:%.*]] = and <2 x i64> [[BC2]], %b
-; CHECK-NEXT:    [[TMP1:%.*]] = bitcast <2 x i64> %a to <4 x i32>
-; CHECK-NEXT:    [[TMP2:%.*]] = bitcast <2 x i64> %b to <4 x i32>
-; CHECK-NEXT:    [[TMP3:%.*]] = select <4 x i1> %cmp, <4 x i32> [[TMP1]], <4 x i32> [[TMP2]]
-; CHECK-NEXT:    [[TMP4:%.*]] = bitcast <4 x i32> [[TMP3]] to <2 x i64>
+; CHECK-NEXT:    [[OR:%.*]] = or <2 x i64> [[AND2]], [[AND1]]
 ; CHECK-NEXT:    [[ADD:%.*]] = add <2 x i64> [[AND2]], [[BC2]]
-; CHECK-NEXT:    [[SUB:%.*]] = sub <2 x i64> [[TMP4]], [[ADD]]
+; CHECK-NEXT:    [[SUB:%.*]] = sub <2 x i64> [[OR]], [[ADD]]
 ; CHECK-NEXT:    ret <2 x i64> [[SUB]]
 ;
   %sext = sext <4 x i1> %cmp to <4 x i32>