[DSE] Add predicated vector length store support for masked store elimination

In isMaskedStoreOverwrite we process two stores that fully overwrite one
another, here we add support for predicated vector length stores so that
DSE will eliminate this variant of masked stores.

Author: mcberg2021

llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp

@@ -248,28 +248,43 @@ static OverwriteResult isMaskedStoreOverwrite(const Instruction *KillingI,
     return OW_Unknown;
   if (KillingII->getIntrinsicID() != DeadII->getIntrinsicID())
     return OW_Unknown;
-  if (KillingII->getIntrinsicID() == Intrinsic::masked_store) {
-    // Type size.
-    VectorType *KillingTy =
-        cast<VectorType>(KillingII->getArgOperand(0)->getType());
-    VectorType *DeadTy = cast<VectorType>(DeadII->getArgOperand(0)->getType());
-    if (KillingTy->getScalarSizeInBits() != DeadTy->getScalarSizeInBits())
+
+  switch (KillingII->getIntrinsicID()) {
+  case Intrinsic::masked_store:
+  case Intrinsic::vp_store: {
+    const DataLayout &DL = KillingII->getDataLayout();
+    auto *KillingTy = KillingII->getArgOperand(0)->getType();
+    auto *DeadTy = DeadII->getArgOperand(0)->getType();
+    if (DL.getTypeSizeInBits(KillingTy) != DL.getTypeSizeInBits(DeadTy))
       return OW_Unknown;
     // Element count.
-    if (KillingTy->getElementCount() != DeadTy->getElementCount())
+    if (cast<VectorType>(KillingTy)->getElementCount() !=
+        cast<VectorType>(DeadTy)->getElementCount())
       return OW_Unknown;
     // Pointers.
-    Value *KillingPtr = KillingII->getArgOperand(1)->stripPointerCasts();
-    Value *DeadPtr = DeadII->getArgOperand(1)->stripPointerCasts();
+    auto *KillingPtr = KillingII->getArgOperand(1);
+    auto *DeadPtr = DeadII->getArgOperand(1);
     if (KillingPtr != DeadPtr && !AA.isMustAlias(KillingPtr, DeadPtr))
       return OW_Unknown;
-    // Masks.
-    // TODO: check that KillingII's mask is a superset of the DeadII's mask.
-    if (KillingII->getArgOperand(3) != DeadII->getArgOperand(3))
-      return OW_Unknown;
+    if (KillingII->getIntrinsicID() == Intrinsic::masked_store) {
+      // Masks.
+      // TODO: check that KillingII's mask is a superset of the DeadII's mask.
+      if (KillingII->getArgOperand(3) != DeadII->getArgOperand(3))
+        return OW_Unknown;
+    } else if (KillingII->getIntrinsicID() == Intrinsic::vp_store) {
+      // Masks.
+      // TODO: check that KillingII's mask is a superset of the DeadII's mask.
+      if (KillingII->getArgOperand(2) != DeadII->getArgOperand(2))
+        return OW_Unknown;
+      // Lengths.
+      if (KillingII->getArgOperand(3) != DeadII->getArgOperand(3))
+        return OW_Unknown;
+    }
     return OW_Complete;
   }
-  return OW_Unknown;
+  default:
+    return OW_Unknown;
+  }
 }
 
 /// Return 'OW_Complete' if a store to the 'KillingLoc' location completely

llvm/test/Transforms/DeadStoreElimination/dead-vp.store.ll

@@ -0,0 +1,33 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=dse -S < %s | FileCheck %s
+
+; Test predicated vector length masked stores for elimination
+
+define void @foo(ptr %a, i32 %vl, <vscale x 8 x i32> %v1, <vscale x 8 x i32> %v2) {
+;
+; CHECK-LABEL: @foo(
+; CHECK-NEXT:    [[VP_OP:%.*]] = call <vscale x 8 x i32> @llvm.vp.add.nxv8i32(<vscale x 8 x i32> [[V1:%.*]], <vscale x 8 x i32> [[V2:%.*]], <vscale x 8 x i1> splat (i1 true), i32 [[VL:%.*]])
+; CHECK-NEXT:    call void @llvm.vp.store.nxv8i32.p0(<vscale x 8 x i32> [[VP_OP]], ptr nonnull [[A:%.*]], <vscale x 8 x i1> splat (i1 true), i32 [[VL]]), !alias.scope [[META0:![0-9]+]], !noalias [[META5:![0-9]+]]
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.vp.store.nxv8i32.p0(<vscale x 8 x i32> %v1, ptr nonnull %a, <vscale x 8 x i1> splat (i1 true), i32 %vl), !alias.scope !34, !noalias !37
+  %vp.op = call <vscale x 8 x i32> @llvm.vp.add.nxv8i32(<vscale x 8 x i32> %v1, <vscale x 8 x i32> %v2, <vscale x 8 x i1> splat (i1 true), i32 %vl)
+  call void @llvm.vp.store.nxv8i32.p0(<vscale x 8 x i32> %vp.op, ptr nonnull %a, <vscale x 8 x i1> splat (i1 true), i32 %vl), !alias.scope !34, !noalias !37
+  ret void
+}
+
+declare <vscale x 8 x i32> @llvm.vp.add.nxv8i32(<vscale x 8 x i32>, <vscale x 8 x i32>, <vscale x 8 x i1>, i32)
+declare void @llvm.vp.store.nxv8i32.p0(<vscale x 8 x i32>, ptr nocapture, <vscale x 8 x i1>, i32)
+
+!11 = !{!"omnipotent char", !12, i64 0}
+!12 = !{!"Simple C/C++ TBAA"}
+!13 = !{!"int", !11, i64 0}
+!16 = !{!13, !13, i64 0}
+!28 = distinct !{!28, !"LVerDomain"}
+!30 = distinct !{!30, !"LVerDomain"}
+!34 = !{!35, !36}
+!35 = distinct !{!35, !28}
+!36 = distinct !{!36, !30}
+!37 = !{!38, !39}
+!38 = distinct !{!38, !28}
+!39 = distinct !{!39, !28}