Make sure flatten globals doesn't insert uses of globals that previously had no uses.

This was the deeper cause of the issues I fixed in https://codereview.chromium.org/33233002/ and is therefore a better fix. (The problem was that StripDeadPrototypes was not stripping a variable that was actually dead because the bitcast constexpr inserted by FlattenGlobals referred to it.) I reverted most of that CL's changes, though not the comment and test cleanup.

R=dschuff@chromium.org
TEST= pnacl-clang++ pnacl/git/libcxx/test/input.output/iostream.objects/narrow.stream.objects/clog.pass.cpp -stdlib=libc++

Review URL: https://codereview.chromium.org/34843003

3 files changed, 4 insertions, 16 deletions

diff --git a/lib/Transforms/NaCl/FlattenGlobals.cpp b/lib/Transforms/NaCl/FlattenGlobals.cpp
index 74ecda168e..11d4466235 100644
--- a/lib/Transforms/NaCl/FlattenGlobals.cpp
+++ b/lib/Transforms/NaCl/FlattenGlobals.cpp
@@ -286,8 +286,9 @@ bool FlattenGlobals::runOnModule(Module &M) {
       NewGlobal->setAlignment(DL.getPrefTypeAlignment(GlobalType));
     NewGlobal->setExternallyInitialized(Global->isExternallyInitialized());
     NewGlobal->takeName(Global);
-    Global->replaceAllUsesWith(
-        ConstantExpr::getBitCast(NewGlobal, Global->getType()));
+    if (!Global->use_empty())
+      Global->replaceAllUsesWith(
+          ConstantExpr::getBitCast(NewGlobal, Global->getType()));
     Global->eraseFromParent();
   }
   return Modified;
diff --git a/lib/Transforms/NaCl/GlobalCleanup.cpp b/lib/Transforms/NaCl/GlobalCleanup.cpp
index d3c58b400a..d489fefc1d 100644
--- a/lib/Transforms/NaCl/GlobalCleanup.cpp
+++ b/lib/Transforms/NaCl/GlobalCleanup.cpp
@@ -84,12 +84,7 @@ bool GlobalCleanup::runOnModule(Module &M) {
   for (Module::global_iterator I = M.global_begin(), E = M.global_end();
        I != E; ) {
     GlobalVariable *GV = I++;
-    if (GV->use_empty()) {
-      GV->eraseFromParent();
-      Modified = true;
-    } else {
-      Modified |= CleanUpLinkage(GV);
-    }
+    Modified |= CleanUpLinkage(GV);
   }
 
   for (Module::iterator I = M.begin(), E = M.end(); I != E; ) {
diff --git a/test/Transforms/NaCl/globalcleanup.ll b/test/Transforms/NaCl/globalcleanup.ll
index 7e1fa3d8a5..5f976e22da 100644
--- a/test/Transforms/NaCl/globalcleanup.ll
+++ b/test/Transforms/NaCl/globalcleanup.ll
@@ -16,14 +16,6 @@
 ; CHECK: @weak_gv = internal global
 @weak_gv = weak global i32 0
 
-; Libc++'s declarations of iostream values are purely ``extern`` and
-; unused otherwise which led to a bug when used as ``(void)std::clog``:
-; the global would survive as ``external global`` post-link but without
-; a proper definition. Global cleanup should take care of it.
-; GV-NOT: ostream
-%"class.fake_ostream" = type { i32 }
-@ostream = external global %"class.fake_ostream"
-
 ; CHECK: define void @_start
 define void @_start() {
   ret void