[modules] Change module manager visitation order to be a bit more stable when

more modules are added: visit modules depth-first rather than breadth-first.
The visitation is still (approximately) oldest-to-newest, and still guarantees
that a module is visited before anything it imports, so modules that are
imported by others sometimes need to jump to a later position in the visitation
order when more modules are loaded, but independent module trees don't
interfere with each other any more.

llvm-svn: 242863

Author: zygoloid

clang/lib/Serialization/ModuleManager.cpp

@@ -316,28 +316,24 @@ ModuleManager::visit(bool (*Visitor)(ModuleFile &M, void *UserData),
     SmallVector<ModuleFile *, 4> Queue;
     Queue.reserve(N);
     llvm::SmallVector<unsigned, 4> UnusedIncomingEdges;
-    UnusedIncomingEdges.reserve(size());
-    for (ModuleIterator M = begin(), MEnd = end(); M != MEnd; ++M) {
-      if (unsigned Size = (*M)->ImportedBy.size())
-        UnusedIncomingEdges.push_back(Size);
-      else {
-        UnusedIncomingEdges.push_back(0);
+    UnusedIncomingEdges.resize(size());
+    for (auto M = rbegin(), MEnd = rend(); M != MEnd; ++M) {
+      unsigned Size = (*M)->ImportedBy.size();
+      UnusedIncomingEdges[(*M)->Index] = Size;
+      if (!Size)
         Queue.push_back(*M);
-      }
     }
 
     // Traverse the graph, making sure to visit a module before visiting any
     // of its dependencies.
-    unsigned QueueStart = 0;
-    while (QueueStart < Queue.size()) {
-      ModuleFile *CurrentModule = Queue[QueueStart++];
+    while (!Queue.empty()) {
+      ModuleFile *CurrentModule = Queue.pop_back_val();
       VisitOrder.push_back(CurrentModule);
 
       // For any module that this module depends on, push it on the
       // stack (if it hasn't already been marked as visited).
-      for (llvm::SetVector<ModuleFile *>::iterator
-             M = CurrentModule->Imports.begin(),
-             MEnd = CurrentModule->Imports.end();
+      for (auto M = CurrentModule->Imports.rbegin(),
+                MEnd = CurrentModule->Imports.rend();
            M != MEnd; ++M) {
         // Remove our current module as an impediment to visiting the
         // module we depend on. If we were the last unvisited module

clang/test/Modules/macros.c

@@ -1,5 +1,6 @@
 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -x objective-c -verify -fmodules-cache-path=%t -I %S/Inputs %s
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -x objective-c -verify -fmodules-cache-path=%t -I %S/Inputs %s -DALT
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -x objective-c -verify -fmodules-cache-path=%t -I %S/Inputs %s -detailed-preprocessing-record
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -DLOCAL_VISIBILITY -fmodules-local-submodule-visibility -x objective-c++ -verify -fmodules-cache-path=%t -I %S/Inputs %s
 // RUN: not %clang_cc1 -E -fmodules -fimplicit-module-maps -x objective-c -fmodules-cache-path=%t -I %S/Inputs %s | FileCheck -check-prefix CHECK-PREPROCESSED %s
@@ -157,6 +158,10 @@ int TOP_DEF_RIGHT_UNDEF; // ok, no longer defined
 # endif
 #endif
 
+#ifdef ALT
+int tmp = TOP_OTHER_REDEF1;
+#endif
+
 @import macros_other;
 
 #ifndef TOP_OTHER_UNDEF1
@@ -166,13 +171,13 @@ int TOP_DEF_RIGHT_UNDEF; // ok, no longer defined
 #ifndef TOP_OTHER_UNDEF2
 # error TOP_OTHER_UNDEF2 should still be defined
 #endif
-
+#pragma clang __debug macro TOP_OTHER_REDEF1
 #ifndef TOP_OTHER_REDEF1
 # error TOP_OTHER_REDEF1 should still be defined
 #endif
 int n1 = TOP_OTHER_REDEF1; // expected-warning{{ambiguous expansion of macro 'TOP_OTHER_REDEF1'}}
-// expected-note@macros_top.h:19 {{expanding this definition}}
-// expected-note@macros_other.h:4 {{other definition}}
+// expected-note@macros_other.h:4 {{expanding this definition}}
+// expected-note@macros_top.h:19 {{other definition}}
 
 #ifndef TOP_OTHER_REDEF2
 # error TOP_OTHER_REDEF2 should still be defined