[llvm] [DebugInfo] Make DISubprogram's hashing always produce the same result (PR #90770)

[Augusto Noronha via llvm-commits]

================
@@ -825,19 +825,26 @@ template <> struct MDNodeKeyImpl<DISubprogram> {
   bool isDefinition() const { return SPFlags & DISubprogram::SPFlagDefinition; }
 
   unsigned getHashValue() const {
+    // Use the Scope's linkage name instead of using the scope directly, as the
+    // scope may be a temporary one which can replaced, which would produce a
+    // different hash for the same DISubprogram.
+    llvm::StringRef ScopeLinkageName;
+    if (auto *CT = dyn_cast_or_null<DICompositeType>(Scope))
+      if (auto *ID = CT->getRawIdentifier())
+        ScopeLinkageName = ID->getString();
+
     // If this is a declaration inside an ODR type, only hash the type and the
     // name.  Otherwise the hash will be stronger than
     // MDNodeSubsetEqualImpl::isDeclarationOfODRMember().
-    if (!isDefinition() && LinkageName)
-      if (auto *CT = dyn_cast_or_null<DICompositeType>(Scope))
-        if (CT->getRawIdentifier())
-          return hash_combine(LinkageName, Scope);
+    if (!isDefinition() && LinkageName &&
+        isa_and_nonnull<DICompositeType>(Scope))
----------------
augusto2112 wrote:

The `isa_and_nonnull` is there to respect the comment above.

```
    // If this is a declaration inside an ODR type, only hash the type and the
     // name.  Otherwise the hash will be stronger than
     // MDNodeSubsetEqualImpl::isDeclarationOfODRMember().
```

Otherwise we'd use the earlier hash for every declaration.

I guess I could check if `ScopeLinkageName` is set instead, could a composite type have no linkage name?

https://github.com/llvm/llvm-project/pull/90770