[GlobalMerge] Exit early if only one global is to be merged

To save some compilation time and prevent some unnecessary changes.

Differential Revision: https://reviews.llvm.org/D46640

llvm-svn: 332813

1 files changed, 9 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/GlobalMerge.cpp b/llvm/lib/CodeGen/GlobalMerge.cpp
index cda5861f676..fbf94d2bb7f 100644
--- a/llvm/lib/CodeGen/GlobalMerge.cpp
+++ b/llvm/lib/CodeGen/GlobalMerge.cpp
@@ -445,6 +445,7 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
   LLVM_DEBUG(dbgs() << " Trying to merge set, starts with #"
                     << GlobalSet.find_first() << "\n");
 
+  bool Changed = false;
   ssize_t i = GlobalSet.find_first();
   while (i != -1) {
     ssize_t j = 0;
@@ -469,6 +470,12 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
       }
     }
 
+    // Exit early if there is only one global to merge.
+    if (Tys.size() < 2) {
+      i = j;
+      continue;
+    }
+
     // If merged variables doesn't have external linkage, we needn't to expose
     // the symbol after merging.
     GlobalValue::LinkageTypes Linkage = HasExternal
@@ -526,10 +533,11 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
 
       NumMerged++;
     }
+    Changed = true;
     i = j;
   }
 
-  return true;
+  return Changed;
 }
 
 void GlobalMerge::collectUsedGlobalVariables(Module &M) {