From 583fe8f2032099d63c12d2da2196f62b92a3e2af Mon Sep 17 00:00:00 2001
From: John Brawn <john.brawn@arm.com>
Date: Mon, 3 Aug 2015 12:08:41 +0000
Subject: [PATCH] [GlobalMerge] Allow targets to enable merging of extern
 variables, NFC.

Adjust the GlobalMergeOnExternal option so that the default behaviour is to
do whatever the Target thinks is best. Explicitly enabled or disabling the
option will override this default.

Differential Revision: http://reviews.llvm.org/D10965


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243873 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Transforms/Scalar.h |  3 ++-
 lib/CodeGen/GlobalMerge.cpp      | 23 +++++++++++++++--------
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/include/llvm/Transforms/Scalar.h b/include/llvm/Transforms/Scalar.h
index 4676c95d7cd..1d6d10f42a7 100644
--- a/include/llvm/Transforms/Scalar.h
+++ b/include/llvm/Transforms/Scalar.h
@@ -161,7 +161,8 @@ Pass *createLoopStrengthReducePass();
 // It can also be configured to focus on size optimizations only.
 //
 Pass *createGlobalMergePass(const TargetMachine *TM, unsigned MaximalOffset,
-                            bool OnlyOptimizeForSize = false);
+                            bool OnlyOptimizeForSize = false,
+                            bool MergeExternalByDefault = false);
 
 //===----------------------------------------------------------------------===//
 //
diff --git a/lib/CodeGen/GlobalMerge.cpp b/lib/CodeGen/GlobalMerge.cpp
index 6f9e8394081..04c97f6796c 100644
--- a/lib/CodeGen/GlobalMerge.cpp
+++ b/lib/CodeGen/GlobalMerge.cpp
@@ -108,10 +108,9 @@ EnableGlobalMergeOnConst("global-merge-on-const", cl::Hidden,
 
 // FIXME: this could be a transitional option, and we probably need to remove
 // it if only we are sure this optimization could always benefit all targets.
-static cl::opt<bool>
+static cl::opt<cl::boolOrDefault>
 EnableGlobalMergeOnExternal("global-merge-on-external", cl::Hidden,
-     cl::desc("Enable global merge pass on external linkage"),
-     cl::init(false));
+     cl::desc("Enable global merge pass on external linkage"));
 
 STATISTIC(NumMerged, "Number of globals merged");
 namespace {
@@ -129,6 +128,9 @@ namespace {
     /// FIXME: This could learn about optsize, and be used in the cost model.
     bool OnlyOptimizeForSize;
 
+    /// Whether we should merge global variables that have external linkage.
+    bool MergeExternalGlobals;
+
     bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
                  Module &M, bool isConst, unsigned AddrSpace) const;
     /// \brief Merge everything in \p Globals for which the corresponding bit
@@ -158,9 +160,11 @@ namespace {
     static char ID;             // Pass identification, replacement for typeid.
     explicit GlobalMerge(const TargetMachine *TM = nullptr,
                          unsigned MaximalOffset = 0,
-                         bool OnlyOptimizeForSize = false)
+                         bool OnlyOptimizeForSize = false,
+                         bool MergeExternalGlobals = false)
         : FunctionPass(ID), TM(TM), MaxOffset(MaximalOffset),
-          OnlyOptimizeForSize(OnlyOptimizeForSize) {
+          OnlyOptimizeForSize(OnlyOptimizeForSize),
+          MergeExternalGlobals(MergeExternalGlobals) {
       initializeGlobalMergePass(*PassRegistry::getPassRegistry());
     }
 
@@ -541,7 +545,7 @@ bool GlobalMerge::doInitialization(Module &M) {
     if (I->isDeclaration() || I->isThreadLocal() || I->hasSection())
       continue;
 
-    if (!(EnableGlobalMergeOnExternal && I->hasExternalLinkage()) &&
+    if (!(MergeExternalGlobals && I->hasExternalLinkage()) &&
         !I->hasInternalLinkage())
       continue;
 
@@ -604,6 +608,9 @@ bool GlobalMerge::doFinalization(Module &M) {
 }
 
 Pass *llvm::createGlobalMergePass(const TargetMachine *TM, unsigned Offset,
-                                  bool OnlyOptimizeForSize) {
-  return new GlobalMerge(TM, Offset, OnlyOptimizeForSize);
+                                  bool OnlyOptimizeForSize,
+                                  bool MergeExternalByDefault) {
+  bool MergeExternal = (EnableGlobalMergeOnExternal == cl::BOU_UNSET) ?
+    MergeExternalByDefault : (EnableGlobalMergeOnExternal == cl::BOU_TRUE);
+  return new GlobalMerge(TM, Offset, OnlyOptimizeForSize, MergeExternal);
 }
-- 
2.34.1