[PATCH] D109632: [clang] de-duplicate methods from AST files

[Richard Howell via Phabricator via cfe-commits]

rmaz created this revision.
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This diff will de-duplicate methods read from AST files before
inserting them in to a global method pool list. When reading
ObjCMethodDecl from AST files we can end up with a significant
amount of duplication when modules contain redeclarations of
system framework methods. For instance a common pattern is to
redeclare `-(instancetype)init` with `NS_UNAVAILABLE`, which
results in the entire ObjCMethodList for `init` being serialized
in each module with this redeclaration.

Measuring this against our codebase for files that use `-fmodules`
shows an overall 19% compile time improvement, and in some cases
as much as 79% for files with a lot of modular dependencies.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D109632

Files:
  clang/lib/Serialization/ASTReader.cpp


Index: clang/lib/Serialization/ASTReader.cpp
===================================================================
--- clang/lib/Serialization/ASTReader.cpp
+++ clang/lib/Serialization/ASTReader.cpp
@@ -8181,8 +8181,18 @@
 /// Add the given set of methods to the method list.
 static void addMethodsToPool(Sema &S, ArrayRef<ObjCMethodDecl *> Methods,
                              ObjCMethodList &List) {
-  for (unsigned I = 0, N = Methods.size(); I != N; ++I) {
-    S.addMethodToGlobalList(&List, Methods[I]);
+  // Methods from visited modules can contain a lot of duplicates
+  // when redeclaring methods from system frameworks, for example
+  // when marking -(instancetype)init as NS_UNAVAILABLE.
+  llvm::DenseSet<ObjCMethodDecl *> seen;
+  for (auto *L = &List; L; L = L->getNext()) {
+    seen.insert(L->getMethod());
+  }
+
+  for (auto *M : Methods) {
+    if (seen.insert(M).second) {
+      S.addMethodToGlobalList(&List, M);
+    }
   }
 }
 


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