[clang] [clang] Speed up Decl::getASTContext() (PR #226612)

[Hans Wennborg via cfe-commits]

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@@ -548,7 +548,15 @@ TranslationUnitDecl *Decl::getTranslationUnitDecl() {
 }
 
 ASTContext &Decl::getASTContext() const {
-  return getTranslationUnitDecl()->getASTContext();
+  if (const auto *TUD = dyn_cast<TranslationUnitDecl>(this))
+    return TUD->getASTContext();
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zmodem wrote:

Could you move the cache check first, and skip this type check on the fast path?

https://github.com/llvm/llvm-project/pull/226612