[PATCH] D107793: [InstSimplify] Eliminate vector reverse of a splat vector

[Usman Nadeem via Phabricator via llvm-commits]

mnadeem created this revision.
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  experimental.vector.reverse(splat(X)) -> splat(X)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D107793

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/named-vector-shuffle-reverse.ll


Index: llvm/test/Transforms/InstSimplify/named-vector-shuffle-reverse.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/named-vector-shuffle-reverse.ll
+++ llvm/test/Transforms/InstSimplify/named-vector-shuffle-reverse.ll
@@ -9,4 +9,17 @@
   ret <vscale x 4 x i32> %rev.rev
 }
 
+; Test reverse of a splat is eliminated.
+define <vscale x 4 x i32> @splat_reverse(i32 %a) {
+; CHECK-LABEL: @splat_reverse(
+; CHECK-NEXT:    [[SPLAT_INSERT:%.*]] = insertelement <vscale x 4 x i32> poison, i32 [[A:%.*]], i32 0
+; CHECK-NEXT:    [[SPLAT:%.*]] = shufflevector <vscale x 4 x i32> [[SPLAT_INSERT]], <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
+; CHECK-NEXT:    ret <vscale x 4 x i32> [[SPLAT]]
+;
+  %splat_insert = insertelement <vscale x 4 x i32> poison, i32 %a, i32 0
+  %splat = shufflevector <vscale x 4 x i32> %splat_insert, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
+  %rev = tail call <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32> %splat)
+  ret <vscale x 4 x i32> %rev
+}
+
 declare <vscale x 4 x i32> @llvm.experimental.vector.reverse.nxv4i32(<vscale x 4 x i32>)
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5457,6 +5457,9 @@
     if (match(Op0,
               m_Intrinsic<Intrinsic::experimental_vector_reverse>(m_Value(X))))
       return X;
+    // experimental.vector.reverse(splat(X)) -> splat(X)
+    if (isSplatValue(Op0))
+      return Op0;
     break;
   default:
     break;


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