[PATCH] D125951: [InstCombine] bitcast (extractelement <1 x elt>, dest) -> bitcast(<1 x elt>, dest)

[Chenbing.Zheng via Phabricator via llvm-commits]

Chenbing.Zheng updated this revision to Diff 432455.
Chenbing.Zheng added a comment.

address comment and rebase tests


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D125951/new/

https://reviews.llvm.org/D125951

Files:
  llvm/include/llvm/IR/Type.h
  llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
  llvm/test/Transforms/InstCombine/bitcast-inseltpoison.ll
  llvm/test/Transforms/InstCombine/bitcast.ll


Index: llvm/test/Transforms/InstCombine/bitcast.ll
===================================================================
--- llvm/test/Transforms/InstCombine/bitcast.ll
+++ llvm/test/Transforms/InstCombine/bitcast.ll
@@ -402,14 +402,9 @@
   ret i64 %bc2
 }
 
-; TODO: This should return %A.
-
 define <2 x i32> @bitcast_extelt3(<2 x i32> %A) {
 ; CHECK-LABEL: @bitcast_extelt3(
-; CHECK-NEXT:    [[BC1:%.*]] = bitcast <2 x i32> [[A:%.*]] to <1 x i64>
-; CHECK-NEXT:    [[EXT:%.*]] = extractelement <1 x i64> [[BC1]], i64 0
-; CHECK-NEXT:    [[BC2:%.*]] = bitcast i64 [[EXT]] to <2 x i32>
-; CHECK-NEXT:    ret <2 x i32> [[BC2]]
+; CHECK-NEXT:    ret <2 x i32> [[A:%.*]]
 ;
   %bc1 = bitcast <2 x i32> %A to <1 x i64>
   %ext = extractelement <1 x i64> %bc1, i32 0
@@ -433,8 +428,7 @@
 
 define <2 x i32> @bitcast_extelt5(<1 x i64> %A) {
 ; CHECK-LABEL: @bitcast_extelt5(
-; CHECK-NEXT:    [[EXT:%.*]] = extractelement <1 x i64> [[A:%.*]], i64 0
-; CHECK-NEXT:    [[BC:%.*]] = bitcast i64 [[EXT]] to <2 x i32>
+; CHECK-NEXT:    [[BC:%.*]] = bitcast <1 x i64> [[A:%.*]] to <2 x i32>
 ; CHECK-NEXT:    ret <2 x i32> [[BC]]
 ;
   %ext = extractelement <1 x i64> %A, i32 0
Index: llvm/test/Transforms/InstCombine/bitcast-inseltpoison.ll
===================================================================
--- llvm/test/Transforms/InstCombine/bitcast-inseltpoison.ll
+++ llvm/test/Transforms/InstCombine/bitcast-inseltpoison.ll
@@ -353,14 +353,9 @@
   ret i64 %bc2
 }
 
-; TODO: This should return %A.
-
 define <2 x i32> @bitcast_extelt3(<2 x i32> %A) {
 ; CHECK-LABEL: @bitcast_extelt3(
-; CHECK-NEXT:    [[BC1:%.*]] = bitcast <2 x i32> [[A:%.*]] to <1 x i64>
-; CHECK-NEXT:    [[EXT:%.*]] = extractelement <1 x i64> [[BC1]], i64 0
-; CHECK-NEXT:    [[BC2:%.*]] = bitcast i64 [[EXT]] to <2 x i32>
-; CHECK-NEXT:    ret <2 x i32> [[BC2]]
+; CHECK-NEXT:    ret <2 x i32> [[A:%.*]]
 ;
   %bc1 = bitcast <2 x i32> %A to <1 x i64>
   %ext = extractelement <1 x i64> %bc1, i32 0
Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -2363,13 +2363,20 @@
   // The bitcast must be to a vectorizable type, otherwise we can't make a new
   // type to extract from.
   Type *DestType = BitCast.getType();
-  if (!VectorType::isValidElementType(DestType))
-    return nullptr;
+  VectorType *VecType = cast<VectorType>(VecOp->getType());
+  if (VectorType::isValidElementType(DestType)) {
+    auto *NewVecType = VectorType::get(DestType, VecType);
+    auto *NewBC = IC.Builder.CreateBitCast(VecOp, NewVecType, "bc");
+    return ExtractElementInst::Create(NewBC, Index);
+  }
 
-  auto *NewVecType =
-      VectorType::get(DestType, cast<VectorType>(VecOp->getType()));
-  auto *NewBC = IC.Builder.CreateBitCast(VecOp, NewVecType, "bc");
-  return ExtractElementInst::Create(NewBC, Index);
+  // Only solve DestType is vector to avoid inverse transform in visitBitCast.
+  // bitcast (extractelement <1 x elt>, dest) -> bitcast(<1 x elt>, dest)
+  if (DestType->isVectorTy() && !VecType->isScalableVectorTy() &&
+      cast<FixedVectorType>(VecType)->getNumElements() == 1)
+    return CastInst::Create(Instruction::BitCast, VecOp, DestType);
+
+  return nullptr;
 }
 
 /// Change the type of a bitwise logic operation if we can eliminate a bitcast.
Index: llvm/include/llvm/IR/Type.h
===================================================================
--- llvm/include/llvm/IR/Type.h
+++ llvm/include/llvm/IR/Type.h
@@ -228,6 +228,11 @@
     return getTypeID() == ScalableVectorTyID || getTypeID() == FixedVectorTyID;
   }
 
+  /// True if this is an instance of ScalableVectorType.
+  inline bool isScalableVectorTy() const {
+    return getTypeID() == ScalableVectorTyID;
+  }
+
   /// Return true if this type could be converted with a lossless BitCast to
   /// type 'Ty'. For example, i8* to i32*. BitCasts are valid for types of the
   /// same size only where no re-interpretation of the bits is done.


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