If a global constant is dead then global's debug info should not prevent the optimizer in deleting the global. And while deleting global, delete global's debug info also.

llvm-svn: 65994

1 files changed, 20 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index 0a35fa93e43..28cd902472d 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -137,15 +137,23 @@ struct VISIBILITY_HIDDEN GlobalStatus {
 }
 
 /// ConstantIsDead - Return true if the specified constant is (transitively)
-/// dead.  The constant may be used by other constants (e.g. constant arrays and
-/// constant exprs) as long as they are dead, but it cannot be used by anything
-/// else.
-static bool ConstantIsDead(Constant *C) {
+/// dead.  The constant may be used by other constants (e.g. constant arrays,
+/// constant exprs, constant global variables) as long as they are dead, 
+/// but it cannot be used by anything else. If DeadGVs is not null then
+/// record dead constant GV users.
+static bool ConstantIsDead(Constant *C, 
+                           SmallPtrSet<GlobalVariable *, 4> *DeadGVs = false) {
+  if (GlobalVariable *GV = dyn_cast<GlobalVariable>(C))
+    if (GV->hasLocalLinkage() && GV->use_empty()) {
+      if (DeadGVs)
+        DeadGVs->insert(GV);
+      return true;
+    }
   if (isa<GlobalValue>(C)) return false;
 
   for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI)
     if (Constant *CU = dyn_cast<Constant>(*UI)) {
-      if (!ConstantIsDead(CU)) return false;
+      if (!ConstantIsDead(CU, DeadGVs)) return false;
     } else
       return false;
   return true;
@@ -338,7 +346,13 @@ static bool CleanupConstantGlobalUsers(Value *V, Constant *Init) {
     } else if (Constant *C = dyn_cast<Constant>(U)) {
       // If we have a chain of dead constantexprs or other things dangling from
       // us, and if they are all dead, nuke them without remorse.
-      if (ConstantIsDead(C)) {
+      SmallPtrSet<GlobalVariable *, 4> DeadGVs;
+      if (ConstantIsDead(C, &DeadGVs)) {
+        for (SmallPtrSet<GlobalVariable *, 4>::iterator TI = DeadGVs.begin(),
+               TE = DeadGVs.end(); TI != TE; ) {
+          GlobalVariable *TGV = *TI; ++TI;
+          TGV->eraseFromParent();
+        }
         C->destroyConstant();
         // This could have invalidated UI, start over from scratch.
         CleanupConstantGlobalUsers(V, Init);