[llvm] [VPlan] Split VPWidenMemoryInstructionRecipe (NFCI). (PR #87411)

[via llvm-commits]

================
@@ -1048,8 +1047,8 @@ void VPlanTransforms::truncateToMinimalBitwidths(
         assert(cast<VPWidenRecipe>(&R)->getOpcode() == Instruction::ICmp &&
                "Only ICmps should not need extending the result.");
 
-      if (isa<VPWidenMemoryInstructionRecipe>(&R)) {
-        assert(!cast<VPWidenMemoryInstructionRecipe>(&R)->isStore() && "stores cannot be narrowed");
+      assert(!isa<VPWidenStoreRecipe>(&R) && "stores cannot be narrowed");
+      if (isa<VPWidenLoadRecipe>(&R)) {
         continue;
       }
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ayalz wrote:

```suggestion
      if (isa<VPWidenLoadRecipe>(&R))
        continue;
```

https://github.com/llvm/llvm-project/pull/87411