From e2a1fa35dfba8efbec2d4468d1dc44c7ecf7f2d7 Mon Sep 17 00:00:00 2001
From: Bruno Cardoso Lopes <bruno.cardoso@gmail.com>
Date: Mon, 25 Aug 2014 17:51:14 +0000
Subject: [PATCH] Remove dangling initializers in GlobalDCE

GlobalDCE deletes global vars and updates their initializers to nullptr
while leaving underlying constants to be cleaned up later by its uses.
The clean up may never happen, fix this by forcing it every time it's
safe to destroy constants.

Final patch by Rafael Espindola
http://reviews.llvm.org/D4931

<rdar://problem/17523868>

llvm-svn: 216390
---
 llvm/lib/Transforms/IPO/GlobalDCE.cpp           |  8 +++++++-
 llvm/lib/Transforms/Utils/GlobalStatus.cpp      |  3 +++
 llvm/test/Transforms/GlobalDCE/deadblockaddr.ll | 16 ++++++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/Transforms/GlobalDCE/deadblockaddr.ll

diff --git a/llvm/lib/Transforms/IPO/GlobalDCE.cpp b/llvm/lib/Transforms/IPO/GlobalDCE.cpp
index 7e7a4c0ae835..e50cdb7358cf 100644
--- a/llvm/lib/Transforms/IPO/GlobalDCE.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalDCE.cpp
@@ -22,6 +22,7 @@
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Transforms/Utils/CtorUtils.h"
+#include "llvm/Transforms/Utils/GlobalStatus.h"
 #include "llvm/Pass.h"
 using namespace llvm;
 
@@ -141,7 +142,12 @@ bool GlobalDCE::runOnModule(Module &M) {
        I != E; ++I)
     if (!AliveGlobals.count(I)) {
       DeadGlobalVars.push_back(I);         // Keep track of dead globals
-      I->setInitializer(nullptr);
+      if (I->hasInitializer()) {
+        Constant *Init = I->getInitializer();
+        I->setInitializer(nullptr);
+        if (isSafeToDestroyConstant(Init))
+          Init->destroyConstant();
+      }
     }
 
   // The second pass drops the bodies of functions which are dead...
diff --git a/llvm/lib/Transforms/Utils/GlobalStatus.cpp b/llvm/lib/Transforms/Utils/GlobalStatus.cpp
index 33e34a9941e0..97a0b4ee5ac9 100644
--- a/llvm/lib/Transforms/Utils/GlobalStatus.cpp
+++ b/llvm/lib/Transforms/Utils/GlobalStatus.cpp
@@ -35,6 +35,9 @@ bool llvm::isSafeToDestroyConstant(const Constant *C) {
   if (isa<GlobalValue>(C))
     return false;
 
+  if (isa<ConstantInt>(C) || isa<ConstantFP>(C))
+    return false;
+
   for (const User *U : C->users())
     if (const Constant *CU = dyn_cast<Constant>(U)) {
       if (!isSafeToDestroyConstant(CU))
diff --git a/llvm/test/Transforms/GlobalDCE/deadblockaddr.ll b/llvm/test/Transforms/GlobalDCE/deadblockaddr.ll
new file mode 100644
index 000000000000..1ec5994d0043
--- /dev/null
+++ b/llvm/test/Transforms/GlobalDCE/deadblockaddr.ll
@@ -0,0 +1,16 @@
+; RUN: opt -globaldce -simplifycfg -S < %s | FileCheck %s
+
+; Tests whether globaldce does the right cleanup while removing @bar
+; so that a dead BlockAddress reference to foo won't prevent other passes
+; to work properly, e.g. simplifycfg
+@bar = internal unnamed_addr constant i8* blockaddress(@foo, %L1)
+
+; CHECK-LABEL: foo
+; CHECK-NOT: br label %L1
+; CHECK: ret void
+define void @foo() {
+entry:
+  br label %L1
+L1:
+  ret void
+}