[PATCH] D73166: [ASTImporter] Properly delete decls from SavedImportPaths

[Jaroslav Sevcik via Phabricator via cfe-commits]

jarin created this revision.
jarin added reviewers: martong, teemperor.
Herald added subscribers: cfe-commits, rnkovacs.
Herald added a reviewer: a.sidorin.
Herald added a reviewer: shafik.
Herald added a project: clang.

We see a significant regression (~40% slower on large codebases) in expression evaluation after https://reviews.llvm.org/rL364771. A sampling profile shows the extra time is spent in SavedImportPathsTy::operator[] when called from ASTImporter::Import. I believe this is because ASTImporter::Import adds an element to the SavedImportPaths map for each decl unconditionally (see https://github.com/llvm/llvm-project/blob/7b81c3f8793d30a4285095a9b67dcfca2117916c/clang/lib/AST/ASTImporter.cpp#L8256).

To fix this, we call SavedImportPathsTy::erase on the declaration rather than clearing its value vector. That way we do not accidentally introduce new empty elements.  (With this patch the performance is restored, and we do not see SavedImportPathsTy::operator[] in the profile anymore.)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73166

Files:
  clang/lib/AST/ASTImporter.cpp


Index: clang/lib/AST/ASTImporter.cpp
===================================================================
--- clang/lib/AST/ASTImporter.cpp
+++ clang/lib/AST/ASTImporter.cpp
@@ -8241,7 +8241,7 @@
           // FIXME Should we remove these Decls from the LookupTable,
           // and from ImportedFromDecls?
       }
-    SavedImportPaths[FromD].clear();
+    SavedImportPaths.erase(FromD);
 
     // Do not return ToDOrErr, error was taken out of it.
     return make_error<ImportError>(ErrOut);
@@ -8274,7 +8274,7 @@
   Imported(FromD, ToD);
 
   updateFlags(FromD, ToD);
-  SavedImportPaths[FromD].clear();
+  SavedImportPaths.erase(FromD);
   return ToDOrErr;
 }
 


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