[clang] [LifetimeSafety] Cache lifetimebound macro lookup. NFC. (PR #205250)

[via cfe-commits]

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@@ -442,21 +442,94 @@ class LifetimeSafetySemaHelperImpl : public LifetimeSafetySemaHelper {
   }
 
 private:
+  struct LifetimeBoundMacroCache {
+    bool IsBuilt = false;
+    SmallVector<const IdentifierInfo *> Candidates;
+  };
+
+  void buildLifetimeBoundMacroCache(LifetimeBoundMacroCache &Cache,
+                                    ArrayRef<TokenValue> Tokens) {
+    if (Cache.IsBuilt)
+      return;
+
+    const Preprocessor &PP = S.getPreprocessor();
+    // Collect macro names that were ever defined as a lifetimebound attribute.
+    for (const auto &M : PP.macros()) {
+      const IdentifierInfo *II = M.first;
+      const MacroDirective *MD = PP.getLocalMacroDirectiveHistory(II);
+      if (!MD)
+        continue;
+
+      // Include earlier matching definitions to handle redefinitions.
+      for (MacroDirective::DefInfo Def = MD->getDefinition(); Def;
+           Def = Def.getPreviousDefinition()) {
+        const MacroInfo *MI = Def.getMacroInfo();
+        if (MI->isObjectLike() && Tokens.size() == MI->getNumTokens() &&
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NeKon69 wrote:

I remember we had some plans for adding lifetimebound(2) kind of annotations, so this first check might interfere with that, but that's a long shot (since most of this won't work anyways with parameters to lifetimebound as their spelling will differ), so probably should be fine.

https://github.com/llvm/llvm-project/pull/205250