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

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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

llvm-svn: 274932
This commit is contained in:
Sanjay Patel 2016-07-08 21:17:51 +00:00
parent 4a31e38dc3
commit 0aed7c7891
2 changed files with 6 additions and 7 deletions
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4
lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View File

@ -1619,8 +1619,8 @@ static Value *matchSelectFromAndOr(Value *A, Value *C, Value *B, Value *D,
// 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;
}

9
test/Transforms/InstCombine/logical-select.ll
View File

@ -265,15 +265,14 @@ define <2 x i64> @bitcast_select_swap7(<4 x i1> %cmp, <2 x double> %a, <2 x doub
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>