[clang] [AST] Iterate redecls starting from the canonical one in getRawCommentsForAnyRedecl() (PR #108475)

[Younan Zhang via cfe-commits]

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@@ -440,14 +440,23 @@ const RawComment *ASTContext::getRawCommentForAnyRedecl(
 
   // Any redeclarations of D that we haven't checked for comments yet?
   // We can't use DenseMap::iterator directly since it'd get invalid.
-  auto LastCheckedRedecl = [this, CanonicalD]() -> const Decl * {
-    return CommentlessRedeclChains.lookup(CanonicalD);
-  }();
+  const Decl *LastCheckedRedecl = CommentlessRedeclChains.lookup(CanonicalD);
+  bool CanUseCommentlessCache = false;
+  if (LastCheckedRedecl) {
+    for (auto *Redecl : CanonicalD->redecls()) {
+      if (Redecl == D) {
+        CanUseCommentlessCache = true;
+        break;
+      }
+      if (Redecl == LastCheckedRedecl)
+        break;
+    }
+  }
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zyn0217 wrote:

Probably, we could move the logic to the lambda and just let the lambda return a nullptr when we're sure that `CanUseCommentlessCache` is false. This could save up the bool variable, WDYT?

(And you can also leave a FIXME here suggesting the algorithm could be improved in that `LastCheckedRedecl` would become useful again once we have traversed past the CanoncialDecl even if `CanUseCommentlessCache` is false.)

https://github.com/llvm/llvm-project/pull/108475