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[InstCombine] improve demanded vector elements analysis of insertelement 

Recurse instead of returning on the first found optimization. Also, return early in the caller
instead of continuing because that allows another round of simplification before we might
potentially lose undef information from a shuffle mask by eliminating the shuffle.

As noted in the review, we could probably do better and be more efficient by moving all of
demanded elements into a separate pass, but this is yet another quick fix to instcombine.

Differential Revision: https://reviews.llvm.org/D37236

llvm-svn: 312248
This commit is contained in:
Sanjay Patel 2017-08-31 15:57:17 +00:00
parent 08f5fd51cc
commit e6b48a1b02
4 changed files with 19 additions and 26 deletions
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19
llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
View File

@ -993,22 +993,23 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
break;
}
// The element inserted overwrites whatever was there, so the input demanded
// set is simpler than the output set.
unsigned IdxNo = Idx->getZExtValue();
APInt PreInsertDemandedElts = DemandedElts;
if (IdxNo < VWidth)
PreInsertDemandedElts.clearBit(IdxNo);
TmpV = SimplifyDemandedVectorElts(I->getOperand(0), PreInsertDemandedElts,
UndefElts, Depth + 1);
if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; }
// If this is inserting an element that isn't demanded, remove this
// insertelement.
unsigned IdxNo = Idx->getZExtValue();
if (IdxNo >= VWidth || !DemandedElts[IdxNo]) {
Worklist.Add(I);
return I->getOperand(0);
}
// Otherwise, the element inserted overwrites whatever was there, so the
// input demanded set is simpler than the output set.
APInt DemandedElts2 = DemandedElts;
DemandedElts2.clearBit(IdxNo);
TmpV = SimplifyDemandedVectorElts(I->getOperand(0), DemandedElts2,
UndefElts, Depth + 1);
if (TmpV) { I->setOperand(0, TmpV); MadeChange = true; }
// The inserted element is defined.
UndefElts.clearBit(IdxNo);
break;

4
llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
View File

@ -1165,9 +1165,7 @@ Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
if (Value *V = SimplifyDemandedVectorElts(&SVI, AllOnesEltMask, UndefElts)) {
if (V != &SVI)
return replaceInstUsesWith(SVI, V);
LHS = SVI.getOperand(0);
RHS = SVI.getOperand(1);
MadeChange = true;
return &SVI;
}
unsigned LHSWidth = LHS->getType()->getVectorNumElements();

5
llvm/test/Transforms/InstCombine/X86/x86-pshufb.ll
View File

@ -485,9 +485,8 @@ define <16 x i8> @demanded_elts_insertion(<16 x i8> %InVec, <16 x i8> %BaseMask,
define <32 x i8> @demanded_elts_insertion_avx2(<32 x i8> %InVec, <32 x i8> %BaseMask, i8 %M0, i8 %M22) {
; CHECK-LABEL: @demanded_elts_insertion_avx2(
; CHECK-NEXT: [[TMP1:%.*]] = insertelement <32 x i8> %BaseMask, i8 %M0, i32 0
; CHECK-NEXT: [[TMP2:%.*]] = tail call <32 x i8> @llvm.x86.avx2.pshuf.b(<32 x i8> %InVec, <32 x i8> [[TMP1]])
; CHECK-NEXT: ret <32 x i8> [[TMP2]]
; CHECK-NEXT: [[TMP1:%.*]] = tail call <32 x i8> @llvm.x86.avx2.pshuf.b(<32 x i8> %InVec, <32 x i8> %BaseMask)
; CHECK-NEXT: ret <32 x i8> [[TMP1]]
;
%1 = insertelement <32 x i8> %BaseMask, i8 %M0, i32 0
%2 = insertelement <32 x i8> %1, i8 %M22, i32 22

17
llvm/test/Transforms/InstCombine/vec_demanded_elts.ll
View File

@ -142,13 +142,11 @@ define <2 x i64> @PR24922(<2 x i64> %v) {
ret <2 x i64> %result
}
; FIXME: The shuffle only demands the 0th (undef) element of 'out123', so everything should fold away.
; The shuffle only demands the 0th (undef) element of 'out123', so everything should fold away.
define <4 x float> @inselt_shuf_no_demand(float %a1, float %a2, float %a3) {
; CHECK-LABEL: @inselt_shuf_no_demand(
; CHECK-NEXT: [[OUT1:%.*]] = insertelement <4 x float> undef, float %a1, i32 1
; CHECK-NEXT: [[OUT12:%.*]] = insertelement <4 x float> [[OUT1]], float %a2, i32 2
; CHECK-NEXT: ret <4 x float> [[OUT12]]
; CHECK-NEXT: ret <4 x float> undef
;
%out1 = insertelement <4 x float> undef, float %a1, i32 1
%out12 = insertelement <4 x float> %out1, float %a2, i32 2
@ -157,13 +155,11 @@ define <4 x float> @inselt_shuf_no_demand(float %a1, float %a2, float %a3) {
ret <4 x float> %shuffle
}
; FIXME: The shuffle only demands the 0th (undef) element of 'out123', so everything should fold away.
; The shuffle only demands the 0th (undef) element of 'out123', so everything should fold away.
define <4 x float> @inselt_shuf_no_demand_commute(float %a1, float %a2, float %a3) {
; CHECK-LABEL: @inselt_shuf_no_demand_commute(
; CHECK-NEXT: [[OUT1:%.*]] = insertelement <4 x float> undef, float %a1, i32 1
; CHECK-NEXT: [[OUT12:%.*]] = insertelement <4 x float> [[OUT1]], float %a2, i32 2
; CHECK-NEXT: ret <4 x float> [[OUT12]]
; CHECK-NEXT: ret <4 x float> undef
;
%out1 = insertelement <4 x float> undef, float %a1, i32 1
%out12 = insertelement <4 x float> %out1, float %a2, i32 2
@ -172,15 +168,14 @@ define <4 x float> @inselt_shuf_no_demand_commute(float %a1, float %a2, float %a
ret <4 x float> %shuffle
}
; FIXME: The add uses 'out012' giving it multiple uses after the shuffle is transformed to also
; The add uses 'out012' giving it multiple uses after the shuffle is transformed to also
; use 'out012'. The analysis should be able to see past that.
define <4 x i32> @inselt_shuf_no_demand_multiuse(i32 %a0, i32 %a1, <4 x i32> %b) {
; CHECK-LABEL: @inselt_shuf_no_demand_multiuse(
; CHECK-NEXT: [[OUT0:%.*]] = insertelement <4 x i32> undef, i32 %a0, i32 0
; CHECK-NEXT: [[OUT01:%.*]] = insertelement <4 x i32> [[OUT0]], i32 %a1, i32 1
; CHECK-NEXT: [[OUT012:%.*]] = insertelement <4 x i32> [[OUT01]], i32 %a0, i32 2
; CHECK-NEXT: [[FOO:%.*]] = add <4 x i32> [[OUT012]], %b
; CHECK-NEXT: [[FOO:%.*]] = add <4 x i32> [[OUT01]], %b
; CHECK-NEXT: ret <4 x i32> [[FOO]]
;
%out0 = insertelement <4 x i32> undef, i32 %a0, i32 0