[PATCH] D71220: [InstCombine] replace shuffle's insertelement operand if inserted scalar is not demanded

[Sanjay Patel via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG396d18aeb6cb: [InstCombine] replace shuffle's insertelement operand if inserted scalar is not… (authored by spatel).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D71220/new/

https://reviews.llvm.org/D71220

Files:
  llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
  llvm/test/Transforms/InstCombine/insert-extract-shuffle.ll


Index: llvm/test/Transforms/InstCombine/insert-extract-shuffle.ll
===================================================================
--- llvm/test/Transforms/InstCombine/insert-extract-shuffle.ll
+++ llvm/test/Transforms/InstCombine/insert-extract-shuffle.ll
@@ -670,7 +670,7 @@
 ; CHECK-LABEL: @insert_undemanded_element_op0(
 ; CHECK-NEXT:    [[INS:%.*]] = insertelement <4 x float> [[X:%.*]], float 4.200000e+01, i32 3
 ; CHECK-NEXT:    call void @use(<4 x float> [[INS]])
-; CHECK-NEXT:    [[S:%.*]] = shufflevector <4 x float> [[INS]], <4 x float> [[Y:%.*]], <4 x i32> <i32 0, i32 7, i32 1, i32 4>
+; CHECK-NEXT:    [[S:%.*]] = shufflevector <4 x float> [[X]], <4 x float> [[Y:%.*]], <4 x i32> <i32 0, i32 7, i32 1, i32 4>
 ; CHECK-NEXT:    ret <4 x float> [[S]]
 ;
   %ins = insertelement <4 x float> %x, float 42.0, i32 3
@@ -683,7 +683,7 @@
 ; CHECK-LABEL: @insert_undemanded_element_op1(
 ; CHECK-NEXT:    [[INS:%.*]] = insertelement <4 x float> [[X:%.*]], float 4.200000e+01, i32 3
 ; CHECK-NEXT:    call void @use(<4 x float> [[INS]])
-; CHECK-NEXT:    [[S:%.*]] = shufflevector <4 x float> [[Y:%.*]], <4 x float> [[INS]], <4 x i32> <i32 3, i32 2, i32 1, i32 4>
+; CHECK-NEXT:    [[S:%.*]] = shufflevector <4 x float> [[Y:%.*]], <4 x float> [[X]], <4 x i32> <i32 3, i32 2, i32 1, i32 4>
 ; CHECK-NEXT:    ret <4 x float> [[S]]
 ;
   %ins = insertelement <4 x float> %x, float 42.0, i32 3
@@ -692,6 +692,8 @@
   ret <4 x float> %s
 }
 
+; Negative test - shuffle chooses the inserted constant.
+
 define <4 x float> @insert_demanded_element_op0(<4 x float> %x, <4 x float> %y) {
 ; CHECK-LABEL: @insert_demanded_element_op0(
 ; CHECK-NEXT:    [[INS:%.*]] = insertelement <4 x float> [[X:%.*]], float 4.200000e+01, i32 3
@@ -705,6 +707,8 @@
   ret <4 x float> %s
 }
 
+; Negative test - shuffle chooses the inserted constant.
+
 define <4 x float> @insert_demanded_element_op1(<4 x float> %x, <4 x float> %y) {
 ; CHECK-LABEL: @insert_demanded_element_op1(
 ; CHECK-NEXT:    [[INS:%.*]] = insertelement <4 x float> [[X:%.*]], float 4.300000e+01, i32 3
Index: llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -1741,7 +1741,8 @@
   return new ShuffleVectorInst(X, Y, ConstantVector::get(NewMask));
 }
 
-/// Try to replace a shuffle with an insertelement.
+/// Try to replace a shuffle with an insertelement or try to replace a shuffle
+/// operand with the operand of an insertelement.
 static Instruction *foldShuffleWithInsert(ShuffleVectorInst &Shuf) {
   Value *V0 = Shuf.getOperand(0), *V1 = Shuf.getOperand(1);
   SmallVector<int, 16> Mask = Shuf.getShuffleMask();
@@ -1753,6 +1754,31 @@
   if (NumElts != (int)(V0->getType()->getVectorNumElements()))
     return nullptr;
 
+  // This is a specialization of a fold in SimplifyDemandedVectorElts. We may
+  // not be able to handle it there if the insertelement has >1 use.
+  // If the shuffle has an insertelement operand but does not choose the
+  // inserted scalar element from that value, then we can replace that shuffle
+  // operand with the source vector of the insertelement.
+  Value *X;
+  uint64_t IdxC;
+  if (match(V0, m_InsertElement(m_Value(X), m_Value(), m_ConstantInt(IdxC)))) {
+    // shuf (inselt X, ?, IdxC), ?, Mask --> shuf X, ?, Mask
+    if (none_of(Mask, [IdxC](int MaskElt) { return MaskElt == (int)IdxC; })) {
+      Shuf.setOperand(0, X);
+      return &Shuf;
+    }
+  }
+  if (match(V1, m_InsertElement(m_Value(X), m_Value(), m_ConstantInt(IdxC)))) {
+    // Offset the index constant by the vector width because we are checking for
+    // accesses to the 2nd vector input of the shuffle.
+    IdxC += NumElts;
+    // shuf ?, (inselt X, ?, IdxC), Mask --> shuf ?, X, Mask
+    if (none_of(Mask, [IdxC](int MaskElt) { return MaskElt == (int)IdxC; })) {
+      Shuf.setOperand(1, X);
+      return &Shuf;
+    }
+  }
+
   // shuffle (insert ?, Scalar, IndexC), V1, Mask --> insert V1, Scalar, IndexC'
   auto isShufflingScalarIntoOp1 = [&](Value *&Scalar, ConstantInt *&IndexC) {
     // We need an insertelement with a constant index.


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