[PATCH] D107254: [VectorUtils] Teach findScalarElement to return splat value.

[Sander de Smalen via Phabricator via llvm-commits]

sdesmalen updated this revision to Diff 363421.
sdesmalen added a comment.

Changed `undef` -> `poison` in test.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D107254/new/

https://reviews.llvm.org/D107254

Files:
  llvm/lib/Analysis/VectorUtils.cpp
  llvm/test/Transforms/InstCombine/vscale_extractelement.ll


Index: llvm/test/Transforms/InstCombine/vscale_extractelement.ll
===================================================================
--- llvm/test/Transforms/InstCombine/vscale_extractelement.ll
+++ llvm/test/Transforms/InstCombine/vscale_extractelement.ll
@@ -243,6 +243,21 @@
   ret i8 %1
 }
 
+define i64* @ext_lane_from_bitcast_of_splat(i32* %v) {
+; CHECK-LABEL: @ext_lane_from_bitcast_of_splat(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[R:%.*]] = bitcast i32* [[V:%.*]] to i64*
+; CHECK-NEXT:    ret i64* [[R]]
+;
+entry:
+  %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*> poison, <vscale x 4 x i32> zeroinitializer
+  %bc = bitcast <vscale x 4 x i32*> %splat to <vscale x 4 x i64*>
+  %r = extractelement <vscale x 4 x i64*> %bc, i32 3
+  ret i64* %r
+}
+
+
 declare <vscale x 4 x i64> @llvm.experimental.stepvector.nxv4i64()
 declare <vscale x 4 x i32> @llvm.experimental.stepvector.nxv4i32()
 declare <vscale x 512 x i8> @llvm.experimental.stepvector.nxv512i8()
Index: llvm/lib/Analysis/VectorUtils.cpp
===================================================================
--- llvm/lib/Analysis/VectorUtils.cpp
+++ llvm/lib/Analysis/VectorUtils.cpp
@@ -323,6 +323,12 @@
     return findScalarElement(SVI->getOperand(1), InEl - LHSWidth);
   }
 
+  // If the vector is a splat then we can trivially find the scalar element.
+  if (isa<ScalableVectorType>(VTy))
+    if (Value *Splat = getSplatValue(V))
+      if (EltNo < VTy->getElementCount().getKnownMinValue())
+        return Splat;
+
   // Extract a value from a vector add operation with a constant zero.
   // TODO: Use getBinOpIdentity() to generalize this.
   Value *Val; Constant *C;


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