[PATCH] D53037: [InstCombine] combine a shuffle and an extract subvector shuffle
Sanjay Patel via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Sun Oct 14 08:27:21 PDT 2018
This revision was automatically updated to reflect the committed changes.
Closed by commit rL344476: [InstCombine] combine a shuffle and an extract subvector shuffle (authored by spatel, committed by ).
Herald added a subscriber: llvm-commits.
Changed prior to commit:
https://reviews.llvm.org/D53037?vs=169088&id=169602#toc
Repository:
rL LLVM
https://reviews.llvm.org/D53037
Files:
llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
llvm/trunk/test/Transforms/InstCombine/vec_shuffle.ll
Index: llvm/trunk/test/Transforms/InstCombine/vec_shuffle.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/vec_shuffle.ll
+++ llvm/trunk/test/Transforms/InstCombine/vec_shuffle.ll
@@ -170,20 +170,18 @@
ret <8 x i8> %t3
}
-; TODO: The mask length of the 1st shuffle can be reduced to eliminate the 2nd shuffle.
+; The mask length of the 1st shuffle can be reduced to eliminate the 2nd shuffle.
define <2 x i8> @extract_subvector_of_shuffle(<2 x i8> %x, <2 x i8> %y) {
; CHECK-LABEL: @extract_subvector_of_shuffle(
-; CHECK-NEXT: [[SHUF:%.*]] = shufflevector <2 x i8> [[X:%.*]], <2 x i8> [[Y:%.*]], <3 x i32> <i32 0, i32 2, i32 undef>
-; CHECK-NEXT: [[EXTRACT_SUBV:%.*]] = shufflevector <3 x i8> [[SHUF]], <3 x i8> undef, <2 x i32> <i32 0, i32 1>
+; CHECK-NEXT: [[EXTRACT_SUBV:%.*]] = shufflevector <2 x i8> [[X:%.*]], <2 x i8> [[Y:%.*]], <2 x i32> <i32 0, i32 2>
; CHECK-NEXT: ret <2 x i8> [[EXTRACT_SUBV]]
;
%shuf = shufflevector <2 x i8> %x, <2 x i8> %y, <3 x i32> <i32 0, i32 2, i32 0>
%extract_subv = shufflevector <3 x i8> %shuf, <3 x i8> undef, <2 x i32> <i32 0, i32 1>
ret <2 x i8> %extract_subv
}
-; TODO:
; Extra uses are ok.
; Undef elements in either mask are ok. Undefs from the 2nd shuffle mask should propagate to the new shuffle.
; The type of the inputs does not have to match the output type.
@@ -194,7 +192,7 @@
; CHECK-LABEL: @extract_subvector_of_shuffle_extra_use(
; CHECK-NEXT: [[SHUF:%.*]] = shufflevector <2 x i8> [[X:%.*]], <2 x i8> [[Y:%.*]], <5 x i32> <i32 undef, i32 2, i32 0, i32 1, i32 0>
; CHECK-NEXT: call void @use_v5i8(<5 x i8> [[SHUF]])
-; CHECK-NEXT: [[EXTRACT_SUBV:%.*]] = shufflevector <5 x i8> [[SHUF]], <5 x i8> undef, <4 x i32> <i32 0, i32 1, i32 2, i32 undef>
+; CHECK-NEXT: [[EXTRACT_SUBV:%.*]] = shufflevector <2 x i8> [[X]], <2 x i8> [[Y]], <4 x i32> <i32 undef, i32 2, i32 0, i32 undef>
; CHECK-NEXT: ret <4 x i8> [[EXTRACT_SUBV]]
;
%shuf = shufflevector <2 x i8> %x, <2 x i8> %y, <5 x i32> <i32 undef, i32 2, i32 0, i32 1, i32 0>
Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -1477,6 +1477,41 @@
return SelectInst::Create(NarrowCond, NarrowX, NarrowY);
}
+/// Try to combine 2 shuffles into 1 shuffle by concatenating a shuffle mask.
+static Instruction *foldIdentityExtractShuffle(ShuffleVectorInst &Shuf) {
+ Value *Op0 = Shuf.getOperand(0), *Op1 = Shuf.getOperand(1);
+ if (!Shuf.isIdentityWithExtract() || !isa<UndefValue>(Op1))
+ return nullptr;
+
+ Value *X, *Y;
+ Constant *Mask;
+ if (!match(Op0, m_ShuffleVector(m_Value(X), m_Value(Y), m_Constant(Mask))))
+ return nullptr;
+
+ // We are extracting a subvector from a shuffle. Remove excess elements from
+ // the 1st shuffle mask to eliminate the extract.
+ //
+ // This transform is conservatively limited to identity extracts because we do
+ // not allow arbitrary shuffle mask creation as a target-independent transform
+ // (because we can't guarantee that will lower efficiently).
+ //
+ // If the extracting shuffle has an undef mask element, it transfers to the
+ // new shuffle mask. Otherwise, copy the original mask element. Example:
+ // shuf (shuf X, Y, <C0, C1, C2, undef, C4>), undef, <0, undef, 2, 3> -->
+ // shuf X, Y, <C0, undef, C2, undef>
+ unsigned NumElts = Shuf.getType()->getVectorNumElements();
+ SmallVector<Constant *, 16> NewMask(NumElts);
+ assert(NumElts < Mask->getType()->getVectorNumElements() &&
+ "Identity with extract must have less elements than its inputs");
+
+ for (unsigned i = 0; i != NumElts; ++i) {
+ Constant *ExtractMaskElt = Shuf.getMask()->getAggregateElement(i);
+ Constant *MaskElt = Mask->getAggregateElement(i);
+ NewMask[i] = isa<UndefValue>(ExtractMaskElt) ? ExtractMaskElt : MaskElt;
+ }
+ return new ShuffleVectorInst(X, Y, ConstantVector::get(NewMask));
+}
+
Instruction *InstCombiner::visitShuffleVectorInst(ShuffleVectorInst &SVI) {
Value *LHS = SVI.getOperand(0);
Value *RHS = SVI.getOperand(1);
@@ -1499,6 +1534,9 @@
return &SVI;
}
+ if (Instruction *I = foldIdentityExtractShuffle(SVI))
+ return I;
+
SmallVector<int, 16> Mask = SVI.getShuffleMask();
Type *Int32Ty = Type::getInt32Ty(SVI.getContext());
unsigned LHSWidth = LHS->getType()->getVectorNumElements();
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