From cd7f205ade20915e16c70a22687af5c3c0ea8923 Mon Sep 17 00:00:00 2001
From: Martin Boehme <mboehme@google.com>
Date: Fri, 24 Apr 2020 17:19:19 +0200
Subject: [PATCH] [IRGen] Check as early as possible for Clang decls we've seen
 before.

Previously, we were only doing this after the fast-path code that
handles decls without any executable code. This meant, however, that we
were potentially processing these decls multiple times. This is
definitely inefficient; it may even be a correctness issue, depending on
what amount of checking `HandleTopLevelDecl` does to see if it has
processed a particular decl before (which I'm not sure about either
way).
---
 lib/IRGen/GenClangDecl.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/IRGen/GenClangDecl.cpp b/lib/IRGen/GenClangDecl.cpp
index 00b5a0e697352..b281db94a0298 100644
--- a/lib/IRGen/GenClangDecl.cpp
+++ b/lib/IRGen/GenClangDecl.cpp
@@ -37,6 +37,10 @@ class ClangDeclRefFinder
 } // end anonymous namespace
 
 void IRGenModule::emitClangDecl(const clang::Decl *decl) {
+  // Ignore this decl if we've seen it before.
+  if (!GlobalClangDecls.insert(decl->getCanonicalDecl()).second)
+    return;
+
   auto valueDecl = dyn_cast<clang::ValueDecl>(decl);
   if (!valueDecl || valueDecl->isExternallyVisible()) {
     ClangCodeGen->HandleTopLevelDecl(
@@ -44,8 +48,6 @@ void IRGenModule::emitClangDecl(const clang::Decl *decl) {
     return;
   }
 
-  if (!GlobalClangDecls.insert(decl->getCanonicalDecl()).second)
-    return;
   SmallVector<const clang::Decl *, 8> stack;
   stack.push_back(decl);