From 0397729d3b8da4208660a163d18296b1a3bd32b8 Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Thu, 14 Jun 2012 22:48:13 +0000
Subject: [PATCH] Implement the isSafeToDiscardIfUnused predicate and use it in
 globalopt and globaldce. Globaldce was already removing linkonce globals, but
 globalopt was not.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158476 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/GlobalValue.h              | 10 ++++++++++
 lib/Transforms/IPO/GlobalDCE.cpp        |  6 +++---
 lib/Transforms/IPO/GlobalOpt.cpp        |  2 +-
 test/Transforms/GlobalOpt/deadglobal.ll | 24 ++++++++++++++++++++----
 4 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/include/llvm/GlobalValue.h b/include/llvm/GlobalValue.h
index 81a11a4c925..8b969f3354c 100644
--- a/include/llvm/GlobalValue.h
+++ b/include/llvm/GlobalValue.h
@@ -164,6 +164,12 @@ public:
     return Linkage == CommonLinkage;
   }
 
+  /// isDiscardableIfUnused - Whether the definition of this global may be
+  /// discarded if it is not used in its compilation unit.
+  static bool isDiscardableIfUnused(LinkageTypes Linkage) {
+    return isLinkOnceLinkage(Linkage) || isLocalLinkage(Linkage);
+  }
+
   /// mayBeOverridden - Whether the definition of this global may be replaced
   /// by something non-equivalent at link time.  For example, if a function has
   /// weak linkage then the code defining it may be replaced by different code.
@@ -221,6 +227,10 @@ public:
   void setLinkage(LinkageTypes LT) { Linkage = LT; }
   LinkageTypes getLinkage() const { return Linkage; }
 
+  bool isDiscardableIfUnused() const {
+    return isDiscardableIfUnused(Linkage);
+  }
+
   bool mayBeOverridden() const { return mayBeOverridden(Linkage); }
 
   bool isWeakForLinker() const { return isWeakForLinker(Linkage); }
diff --git a/lib/Transforms/IPO/GlobalDCE.cpp b/lib/Transforms/IPO/GlobalDCE.cpp
index 2b427aa6a4e..18c1c7b0005 100644
--- a/lib/Transforms/IPO/GlobalDCE.cpp
+++ b/lib/Transforms/IPO/GlobalDCE.cpp
@@ -65,7 +65,7 @@ bool GlobalDCE::runOnModule(Module &M) {
   for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) {
     Changed |= RemoveUnusedGlobalValue(*I);
     // Functions with external linkage are needed if they have a body
-    if (!I->hasLocalLinkage() && !I->hasLinkOnceLinkage() &&
+    if (!I->isDiscardableIfUnused() &&
         !I->isDeclaration() && !I->hasAvailableExternallyLinkage())
       GlobalIsNeeded(I);
   }
@@ -75,7 +75,7 @@ bool GlobalDCE::runOnModule(Module &M) {
     Changed |= RemoveUnusedGlobalValue(*I);
     // Externally visible & appending globals are needed, if they have an
     // initializer.
-    if (!I->hasLocalLinkage() && !I->hasLinkOnceLinkage() &&
+    if (!I->isDiscardableIfUnused() &&
         !I->isDeclaration() && !I->hasAvailableExternallyLinkage())
       GlobalIsNeeded(I);
   }
@@ -84,7 +84,7 @@ bool GlobalDCE::runOnModule(Module &M) {
        I != E; ++I) {
     Changed |= RemoveUnusedGlobalValue(*I);
     // Externally visible aliases are needed.
-    if (!I->hasLocalLinkage() && !I->hasLinkOnceLinkage())
+    if (!I->isDiscardableIfUnused())
       GlobalIsNeeded(I);
   }
 
diff --git a/lib/Transforms/IPO/GlobalOpt.cpp b/lib/Transforms/IPO/GlobalOpt.cpp
index d316d526785..9e3b8c28269 100644
--- a/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/lib/Transforms/IPO/GlobalOpt.cpp
@@ -1716,7 +1716,7 @@ static bool TryToShrinkGlobalToBoolean(GlobalVariable *GV, Constant *OtherVal) {
 /// possible.  If we make a change, return true.
 bool GlobalOpt::ProcessGlobal(GlobalVariable *GV,
                               Module::global_iterator &GVI) {
-  if (!GV->hasLocalLinkage())
+  if (!GV->isDiscardableIfUnused())
     return false;
 
   // Do more involved optimizations if the global is internal.
diff --git a/test/Transforms/GlobalOpt/deadglobal.ll b/test/Transforms/GlobalOpt/deadglobal.ll
index c8d8e7674d6..cad5a91488a 100644
--- a/test/Transforms/GlobalOpt/deadglobal.ll
+++ b/test/Transforms/GlobalOpt/deadglobal.ll
@@ -1,9 +1,25 @@
-; RUN: opt < %s -globalopt -S | not grep internal
+; RUN: opt < %s -globalopt -S | FileCheck %s
 
-@G = internal global i32 123            ; <i32*> [#uses=1]
+@G1 = internal global i32 123            ; <i32*> [#uses=1]
 
-define void @foo() {
-        store i32 1, i32* @G
+; CHECK-NOT: @G1
+; CHECK: @G2
+; CHECK-NOT: @G3
+
+define void @foo1() {
+; CHECK: define void @foo
+; CHECK-NEXT: ret
+        store i32 1, i32* @G1
+        ret void
+}
+
+@G2 = linkonce_odr constant i32 42
+
+define void @foo2() {
+; CHECK: define void @foo2
+; CHECK-NEXT: store
+        store i32 1, i32* @G2
         ret void
 }
 
+@G3 = linkonce_odr constant i32 42
-- 
2.34.1