[PATCH] D102404: [InstCombine] Add instcombine fold for extractelement + splat for scalable vectors

[Caroline via Phabricator via llvm-commits]

CarolineConcatto updated this revision to Diff 348001.
CarolineConcatto added a comment.

- address reviewer's comment
- reduce patch scope to only work with instcombine


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D102404/new/

https://reviews.llvm.org/D102404

Files:
  llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
  llvm/test/Transforms/InstCombine/vscale_extractelement-inseltpoison.ll
  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
@@ -55,13 +55,9 @@
   ret i8 %r
 }
 
-; TODO: Instcombine could optimize to return %v.
 define i32 @extractelement_shuffle_in_range(i32 %v) {
 ; CHECK-LABEL: @extractelement_shuffle_in_range(
-; 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 1
-; 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
Index: llvm/test/Transforms/InstCombine/vscale_extractelement-inseltpoison.ll
===================================================================
--- llvm/test/Transforms/InstCombine/vscale_extractelement-inseltpoison.ll
+++ llvm/test/Transforms/InstCombine/vscale_extractelement-inseltpoison.ll
@@ -55,13 +55,9 @@
   ret i8 %r
 }
 
-; TODO: Instcombine could optimize to return %v.
 define i32 @extractelement_shuffle_in_range(i32 %v) {
 ; CHECK-LABEL: @extractelement_shuffle_in_range(
-; 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> poison, <vscale x 4 x i32> zeroinitializer
-; CHECK-NEXT:    [[R:%.*]] = extractelement <vscale x 4 x i32> [[SPLAT]], i32 1
-; 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> poison, <vscale x 4 x i32> zeroinitializer
Index: llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -347,6 +347,14 @@
     ElementCount EC = EI.getVectorOperandType()->getElementCount();
     unsigned NumElts = EC.getKnownMinValue();
 
+    // It handle cases where splat is the operand of the extract
+    // extractelement (shufflevector (insertelement lane, 0), 0), idx)
+    // It returns the lane value from insert
+    if (auto *SE = dyn_cast<ShuffleVectorInst>(SrcVec))
+      if (isSplatValue(SE) && IndexC->getValue().ult(NumElts))
+        if (auto *IE = dyn_cast<InsertElementInst>(SE->getOperand(0)))
+          return replaceInstUsesWith(EI, IE->getOperand(1));
+
     // InstSimplify should handle cases where the index is invalid.
     // For fixed-length vector, it's invalid to extract out-of-range element.
     if (!EC.isScalable() && IndexC->getValue().uge(NumElts))


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