[llvm] [IR] Allow type change in ValueAsMetadata::handleRAUW (PR #76969)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

Author: Jannik Silvanus (jasilvanus)

<details>
<summary>Changes</summary>

`ValueAsMetadata::handleRAUW` is a mechanism to replace all metadata referring to one value by a different value.

Relax an assert that used to enforce the old and new value to have the same type.
This seems to be a sanity plausibility assert only, as the implementation actually supports mismatching types.

This is motivated by a downstream mechanism where we use poison ValueAsMetadata values to annotate pointee types of opaque pointer function arguments.

When replacing one type with a different one to work around DXIL vs LLVM incompatibilities, we need to update type annotations, and handleRAUW is more efficient than creating new MD nodes.

---
Full diff: https://github.com/llvm/llvm-project/pull/76969.diff


1 Files Affected:

- (modified) llvm/lib/IR/Metadata.cpp (+1-1) 


``````````diff
diff --git a/llvm/lib/IR/Metadata.cpp b/llvm/lib/IR/Metadata.cpp
index 515893d079b8cb..bdfbd8829186d9 100644
--- a/llvm/lib/IR/Metadata.cpp
+++ b/llvm/lib/IR/Metadata.cpp
@@ -503,7 +503,7 @@ void ValueAsMetadata::handleRAUW(Value *From, Value *To) {
   assert(From && "Expected valid value");
   assert(To && "Expected valid value");
   assert(From != To && "Expected changed value");
-  assert(From->getType() == To->getType() && "Unexpected type change");
+  assert(&From->getContext() == &To->getContext() && "Expected same context");
 
   LLVMContext &Context = From->getType()->getContext();
   auto &Store = Context.pImpl->ValuesAsMetadata;

``````````

</details>


https://github.com/llvm/llvm-project/pull/76969