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[InstSimplify] fold extractelement of splat with variable extract index 

We already have a fold for variable index with constant vector,
but if we can determine a scalar splat value, then it does not
matter whether that value is constant or not.

We overlooked this fold in D102404 and earlier patches,
but the fixed vector variant is shown in:
https://llvm.org/PR50817

Alive2 agrees on that:
https://alive2.llvm.org/ce/z/HpijPC

The same logic applies to scalable vectors.

Differential Revision: https://reviews.llvm.org/D104867
This commit is contained in:
Sanjay Patel 2021-07-05 08:14:20 -04:00
parent de8274a1b9
commit 3d3c0ed932
4 changed files with 7 additions and 16 deletions
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8
llvm/lib/Analysis/InstructionSimplify.cpp
View File

@ -4531,10 +4531,6 @@ static Value *SimplifyExtractElementInst(Value *Vec, Value *Idx,
if (auto *CIdx = dyn_cast<Constant>(Idx))
return ConstantExpr::getExtractElement(CVec, CIdx);
// The index is not relevant if our vector is a splat.
if (auto *Splat = CVec->getSplatValue())
return Splat;
if (Q.isUndefValue(Vec))
return UndefValue::get(VecVTy->getElementType());
}
@ -4557,6 +4553,10 @@ static Value *SimplifyExtractElementInst(Value *Vec, Value *Idx,
return Splat;
if (Value *Elt = findScalarElement(Vec, IdxC->getZExtValue()))
return Elt;
} else {
// The index is not relevant if our vector is a splat.
if (Value *Splat = getSplatValue(Vec))
return Splat;
}
return nullptr;
}

5
llvm/test/Transforms/InstSimplify/extract-element.ll
View File

@ -62,10 +62,7 @@ define float @extract_element_splat_constant_vector_variable_index(i32 %y) {
define i32 @extractelement_splat_variable_index(i32 %v, i32 %index) {
; CHECK-LABEL: @extractelement_splat_variable_index(
; CHECK-NEXT: [[IN:%.*]] = insertelement <3 x i32> poison, i32 [[V:%.*]], i32 0
; CHECK-NEXT: [[SPLAT:%.*]] = shufflevector <3 x i32> [[IN]], <3 x i32> poison, <3 x i32> zeroinitializer
; CHECK-NEXT: [[R:%.*]] = extractelement <3 x i32> [[SPLAT]], i32 [[INDEX:%.*]]
; CHECK-NEXT: ret i32 [[R]]
; CHECK-NEXT: ret i32 [[V:%.*]]
;
%in = insertelement <3 x i32> poison, i32 %v, i32 0
%splat = shufflevector <3 x i32> %in, <3 x i32> poison, <3 x i32> zeroinitializer

5
llvm/test/Transforms/InstSimplify/vscale-inseltpoison.ll
View File

@ -210,10 +210,7 @@ define i32 @extractelement_splat_constant_index(i32 %v) {
define i32 @extractelement_splat_variable_index(i32 %v, i32 %idx) {
; CHECK-LABEL: @extractelement_splat_variable_index(
; CHECK-NEXT: [[IN:%.*]] = insertelement <vscale x 4 x i32> poison, i32 [[V:%.*]], i32 0
; CHECK-NEXT: [[SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[IN]], <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer
; CHECK-NEXT: [[R:%.*]] = extractelement <vscale x 4 x i32> [[SPLAT]], i32 [[IDX:%.*]]
; CHECK-NEXT: ret i32 [[R]]
; CHECK-NEXT: ret i32 [[V:%.*]]
;
%in = insertelement <vscale x 4 x i32> poison, i32 %v, i32 0
%splat = shufflevector <vscale x 4 x i32> %in, <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer

5
llvm/test/Transforms/InstSimplify/vscale.ll
View File

@ -210,10 +210,7 @@ define i32 @extractelement_splat_constant_index(i32 %v) {
define i32 @extractelement_splat_variable_index(i32 %v, i32 %idx) {
; CHECK-LABEL: @extractelement_splat_variable_index(
; CHECK-NEXT: [[IN:%.*]] = insertelement <vscale x 4 x i32> undef, i32 [[V:%.*]], i32 0
; CHECK-NEXT: [[SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[IN]], <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer
; CHECK-NEXT: [[R:%.*]] = extractelement <vscale x 4 x i32> [[SPLAT]], i32 [[IDX:%.*]]
; CHECK-NEXT: ret i32 [[R]]
; CHECK-NEXT: ret i32 [[V:%.*]]
;
%in = insertelement <vscale x 4 x i32> undef, i32 %v, i32 0
%splat = shufflevector <vscale x 4 x i32> %in, <vscale x 4 x i32> undef, <vscale x 4 x i32> zeroinitializer