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

[Caroline via Phabricator via llvm-commits]

CarolineConcatto updated this revision to Diff 349282.
CarolineConcatto marked 3 inline comments as done.
CarolineConcatto added a comment.

- Address Sander's comments


Repository:
  rG LLVM Github Monorepo

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

https://reviews.llvm.org/D102404

Files:
  llvm/lib/Analysis/InstructionSimplify.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/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4489,9 +4489,13 @@
   // find a previously computed scalar that was inserted into the vector.
   if (auto *IdxC = dyn_cast<ConstantInt>(Idx)) {
     // For fixed-length vector, fold into undef if index is out of bounds.
-    if (isa<FixedVectorType>(VecVTy) &&
-        IdxC->getValue().uge(cast<FixedVectorType>(VecVTy)->getNumElements()))
+    unsigned MinNumElts = VecVTy->getElementCount().getKnownMinValue();
+    if (isa<FixedVectorType>(VecVTy) && IdxC->getValue().uge(MinNumElts))
       return PoisonValue::get(VecVTy->getElementType());
+    // It handle cases where splat is the operand of the extract
+    if (IdxC->getValue().ult(MinNumElts))
+      if (auto *Splat = getSplatValue(Vec))
+        return Splat;
     if (Value *Elt = findScalarElement(Vec, IdxC->getZExtValue()))
       return Elt;
   }


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