[clang] [clang] Add one-entry cache for ASTContext::getDeclAttrs() (PR #226610)

[Hans Wennborg via cfe-commits]

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@@ -1532,12 +1533,17 @@ DiagnosticsEngine &ASTContext::getDiagnostics() const {
 }
 
 AttrVec& ASTContext::getDeclAttrs(const Decl *D) {
+  if (LastDeclAttrsDecl == D)
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zmodem wrote:

Maybe add a short comment about why having a cache here is beneficial? ("85% of lookups use the most recent D")

https://github.com/llvm/llvm-project/pull/226610