[PATCH] D123413: [IR] Allow constant folding (insertelement <vscale x 2 x i32> zeroinitializer, i32 0, i32 i32 0.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: spatel, sdesmalen, efriedma.
Herald added subscribers: StephenFan, dexonsmith, hiraditya.
Herald added a project: All.
craig.topper requested review of this revision.
Herald added a subscriber: alextsao1999.
Herald added a project: LLVM.

Most of insertelement constant folding is blocked if the vector type
is scalable. I believe we can make an exception for inserting null
into an all zeros vector.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D123413

Files:
  llvm/lib/IR/ConstantFold.cpp
  llvm/test/Transforms/LoopVectorize/AArch64/sve-widen-phi.ll


Index: llvm/test/Transforms/LoopVectorize/AArch64/sve-widen-phi.ll
===================================================================
--- llvm/test/Transforms/LoopVectorize/AArch64/sve-widen-phi.ll
+++ llvm/test/Transforms/LoopVectorize/AArch64/sve-widen-phi.ll
@@ -251,7 +251,7 @@
 ; CHECK:       vector.body:
 ; CHECK-NEXT:    [[POINTER_PHI:%.*]] = phi i32* [ [[A]], [[VECTOR_PH]] ], [ [[PTR_IND:%.*]], [[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, [[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], [[VECTOR_BODY]] ]
-; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <vscale x 2 x i32> [ insertelement (<vscale x 2 x i32> zeroinitializer, i32 0, i32 0), [[VECTOR_PH]] ], [ [[TMP9:%.*]], [[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[VEC_PHI:%.*]] = phi <vscale x 2 x i32> [ zeroinitializer, [[VECTOR_PH]] ], [ [[TMP9:%.*]], [[VECTOR_BODY]] ]
 ; CHECK-NEXT:    [[TMP4:%.*]] = call i64 @llvm.vscale.i64()
 ; CHECK-NEXT:    [[TMP5:%.*]] = shl nuw nsw i64 [[TMP4]], 1
 ; CHECK-NEXT:    [[TMP6:%.*]] = call <vscale x 2 x i64> @llvm.experimental.stepvector.nxv2i64()
Index: llvm/lib/IR/ConstantFold.cpp
===================================================================
--- llvm/lib/IR/ConstantFold.cpp
+++ llvm/lib/IR/ConstantFold.cpp
@@ -686,6 +686,10 @@
   ConstantInt *CIdx = dyn_cast<ConstantInt>(Idx);
   if (!CIdx) return nullptr;
 
+  // Inserting null into all zeros is still all zeros.
+  if (isa<ConstantAggregateZero>(Val) && Elt->isNullValue())
+    return Val;
+
   // Do not iterate on scalable vector. The num of elements is unknown at
   // compile-time.
   if (isa<ScalableVectorType>(Val->getType()))


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