From 72f3c1b1cc1ed1989cbfd649ce33caee52ede172 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sat, 15 Jan 2011 18:14:21 +0000
Subject: [PATCH] Make constmerge a two-pass algorithm so that it won't miss
 merging opporuntities. Fixes PR8978.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123541 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/IPO/ConstantMerge.cpp               | 38 +++++++++++++++++++---
 .../ConstantMerge/2011-01-15-EitherOrder.ll        | 18 ++++++++++
 2 files changed, 52 insertions(+), 4 deletions(-)
 create mode 100644 test/Transforms/ConstantMerge/2011-01-15-EitherOrder.ll

diff --git a/lib/Transforms/IPO/ConstantMerge.cpp b/lib/Transforms/IPO/ConstantMerge.cpp
index ea01ffeeb5..8efad05855 100644
--- a/lib/Transforms/IPO/ConstantMerge.cpp
+++ b/lib/Transforms/IPO/ConstantMerge.cpp
@@ -101,15 +101,18 @@ bool ConstantMerge::runOnModule(Module &M) {
         continue;
       }
       
-      // Only process constants with initializers in the default addres space.
+      // Only process constants with initializers in the default address space.
       if (!GV->isConstant() ||!GV->hasDefinitiveInitializer() ||
-          GV->getType()->getAddressSpace() != 0 || !GV->getSection().empty() ||
+          GV->getType()->getAddressSpace() != 0 || GV->hasSection() ||
           // Don't touch values marked with attribute(used).
           UsedGlobals.count(GV))
         continue;
       
+      // Start by filling slots with only the globals we aren't allowed to
+      // delete because they're externally visible.
+      if (GV->hasLocalLinkage())
+        continue;
       
-      
       Constant *Init = GV->getInitializer();
 
       // Check to see if the initializer is already known.
@@ -117,7 +120,32 @@ bool ConstantMerge::runOnModule(Module &M) {
 
       if (Slot == 0) {    // Nope, add it to the map.
         Slot = GV;
-      } else if (GV->hasLocalLinkage()) {    // Yup, this is a duplicate!
+      }
+    }
+
+    for (Module::global_iterator GVI = M.global_begin(), E = M.global_end();
+         GVI != E; ) {
+      GlobalVariable *GV = GVI++;
+
+      // Only process constants with initializers in the default address space.
+      if (!GV->isConstant() ||!GV->hasDefinitiveInitializer() ||
+          GV->getType()->getAddressSpace() != 0 || GV->hasSection() ||
+          // Don't touch values marked with attribute(used).
+          UsedGlobals.count(GV))
+        continue;
+
+      // Only look at the remaining globals now.
+      if (!GV->hasLocalLinkage())
+        continue;
+
+      Constant *Init = GV->getInitializer();
+
+      // Check to see if the initializer is already known.
+      GlobalVariable *&Slot = CMap[Init];
+
+      if (Slot == 0) {    // Nope, add it to the map.
+        Slot = GV;
+      } else {            // Yup, this is a duplicate!
         // Make all uses of the duplicate constant use the canonical version.
         Replacements.push_back(std::make_pair(GV, Slot));
       }
@@ -135,6 +163,8 @@ bool ConstantMerge::runOnModule(Module &M) {
       Replacements[i].first->replaceAllUsesWith(Replacements[i].second);
 
       // Delete the global value from the module.
+      assert(Replacements[i].first->hasLocalLinkage() &&
+             "Refusing to delete an externally visible global variable.");
       Replacements[i].first->eraseFromParent();
     }
 
diff --git a/test/Transforms/ConstantMerge/2011-01-15-EitherOrder.ll b/test/Transforms/ConstantMerge/2011-01-15-EitherOrder.ll
new file mode 100644
index 0000000000..7001ce1ba4
--- /dev/null
+++ b/test/Transforms/ConstantMerge/2011-01-15-EitherOrder.ll
@@ -0,0 +1,18 @@
+; RUN: opt -constmerge %s -S -o - | FileCheck %s
+; PR8978
+
+declare i32 @zed(%struct.foobar*, %struct.foobar*)
+
+%struct.foobar = type { i32 }
+; CHECK: bar.d
+@bar.d =  constant %struct.foobar zeroinitializer, align 4
+; CHECK-NOT: foo.d
+@foo.d = internal constant %struct.foobar zeroinitializer, align 4
+define i32 @main() nounwind ssp {
+entry:
+; CHECK: bar.d
+  %call2 = tail call i32 @zed(%struct.foobar* @foo.d, %struct.foobar* @bar.d)
+nounwind
+  ret i32 0
+}
+
-- 
2.11.4.GIT