[PATCH] D141625: [DeclContext] Sort the Decls before adding into DeclContext

[Steven Wu via Phabricator via cfe-commits]

steven_wu created this revision.
steven_wu added reviewers: jansvoboda11, akyrtzi, benlangmuir, vsapsai, rnk, dblaikie.
Herald added subscribers: ributzka, mgrang.
Herald added a project: All.
steven_wu requested review of this revision.
Herald added a project: clang.

Fix a non-deterministic issue in clang module generation, which the
anonymous declaration number from a function context is not
deterministic. This is due to the unstable iteration order for decls in
scope so the order after moving the decls into function decl context is
not deterministic.

>From https://reviews.llvm.org/D135118, we can't use a set that preserves
the order without the performance penalty. Fix the issue by sorting the
decls based on raw encoding of their source location.

rdar://104097976


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D141625

Files:
  clang/lib/Parse/ParseDecl.cpp


Index: clang/lib/Parse/ParseDecl.cpp
===================================================================
--- clang/lib/Parse/ParseDecl.cpp
+++ clang/lib/Parse/ParseDecl.cpp
@@ -6986,6 +6986,13 @@
         continue;
       DeclsInPrototype.push_back(ND);
     }
+    // Sort DeclsInPrototype based on raw encoding of the source location. This
+    // provides a stable iterating order in DeclContext, which is important for
+    // tasks like ASTWriter for deterministic output.
+    llvm::sort(DeclsInPrototype, [](Decl *D1, Decl *D2) {
+      return D1->getLocation().getRawEncoding() <
+             D2->getLocation().getRawEncoding();
+    });
   }
 
   // Remember that we parsed a function type, and remember the attributes.


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