[llvm] r216390 - Remove dangling initializers in GlobalDCE

[Bruno Cardoso Lopes]

Author: bruno
Date: Mon Aug 25 12:51:14 2014
New Revision: 216390

URL: http://llvm.org/viewvc/llvm-project?rev=216390&view=rev
Log:
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>

Added:
    llvm/trunk/test/Transforms/GlobalDCE/deadblockaddr.ll
Modified:
    llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp
    llvm/trunk/lib/Transforms/Utils/GlobalStatus.cpp

Modified: llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp?rev=216390&r1=216389&r2=216390&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/GlobalDCE.cpp Mon Aug 25 12:51:14 2014
@@ -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...

Modified: llvm/trunk/lib/Transforms/Utils/GlobalStatus.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/GlobalStatus.cpp?rev=216390&r1=216389&r2=216390&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/GlobalStatus.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/GlobalStatus.cpp Mon Aug 25 12:51:14 2014
@@ -35,6 +35,9 @@ bool llvm::isSafeToDestroyConstant(const
   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))

Added: llvm/trunk/test/Transforms/GlobalDCE/deadblockaddr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GlobalDCE/deadblockaddr.ll?rev=216390&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/GlobalDCE/deadblockaddr.ll (added)
+++ llvm/trunk/test/Transforms/GlobalDCE/deadblockaddr.ll Mon Aug 25 12:51:14 2014
@@ -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
+ at 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
+}