[Modules] Make "#pragma weak" undeclared identifiers be tracked

deterministically.

This fixes a latent issue where even Clang's Sema (and diagnostics) were
non-deterministic in the face of this pragma. The fix is super simple --
just use a MapVector so we track the order in which these are parsed (or
imported). Especially considering how rare they are, this seems like the
perfect tradeoff. I've also simplified the client code with judicious
use of auto and range based for loops.

I've added some pretty hilarious code to my stress test which now
survives the binary diff without issue.

llvm-svn: 233261

1 files changed, 7 insertions, 16 deletions

diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index a1a9b9d0b8c..6825dfa41fa 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -524,14 +524,8 @@ void Sema::LoadExternalWeakUndeclaredIdentifiers() {
 
   SmallVector<std::pair<IdentifierInfo *, WeakInfo>, 4> WeakIDs;
   ExternalSource->ReadWeakUndeclaredIdentifiers(WeakIDs);
-  for (unsigned I = 0, N = WeakIDs.size(); I != N; ++I) {
-    llvm::DenseMap<IdentifierInfo*,WeakInfo>::iterator Pos
-      = WeakUndeclaredIdentifiers.find(WeakIDs[I].first);
-    if (Pos != WeakUndeclaredIdentifiers.end())
-      continue;
-
-    WeakUndeclaredIdentifiers.insert(WeakIDs[I]);
-  }
+  for (auto &WeakID : WeakIDs)
+    WeakUndeclaredIdentifiers.insert(WeakID);
 }
 
 
@@ -694,16 +688,13 @@ void Sema::ActOnEndOfTranslationUnit() {
   }
 
   // Check for #pragma weak identifiers that were never declared
-  // FIXME: This will cause diagnostics to be emitted in a non-determinstic
-  // order!  Iterating over a densemap like this is bad.
   LoadExternalWeakUndeclaredIdentifiers();
-  for (llvm::DenseMap<IdentifierInfo*,WeakInfo>::iterator
-       I = WeakUndeclaredIdentifiers.begin(),
-       E = WeakUndeclaredIdentifiers.end(); I != E; ++I) {
-    if (I->second.getUsed()) continue;
+  for (auto WeakID : WeakUndeclaredIdentifiers) {
+    if (WeakID.second.getUsed())
+      continue;
 
-    Diag(I->second.getLocation(), diag::warn_weak_identifier_undeclared)
-      << I->first;
+    Diag(WeakID.second.getLocation(), diag::warn_weak_identifier_undeclared)
+        << WeakID.first;
   }
 
   if (LangOpts.CPlusPlus11 &&