[MergeFunc] Erase unused duplicate functions if they are discardable

MergeFunc only deletes unused duplicate functions if they have local
linkage, but it should be safe to relax this to any "discardable if
unused" linkage type.

Differential Revision: https://reviews.llvm.org/D56574

llvm-svn: 350939

2 files changed, 14 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/IPO/MergeFunctions.cpp b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
index 30fe9bbbe61..11efe95b10d 100644
--- a/llvm/lib/Transforms/IPO/MergeFunctions.cpp
+++ b/llvm/lib/Transforms/IPO/MergeFunctions.cpp
@@ -845,7 +845,7 @@ void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
     // If G was internal then we may have replaced all uses of G with F. If so,
     // stop here and delete G. There's no need for a thunk. (See note on
     // MergeFunctionsPDI above).
-    if (G->hasLocalLinkage() && G->use_empty() && !MergeFunctionsPDI) {
+    if (G->isDiscardableIfUnused() && G->use_empty() && !MergeFunctionsPDI) {
       G->eraseFromParent();
       ++NumFunctionsMerged;
       return;
diff --git a/llvm/test/Transforms/MergeFunc/linkonce_odr.ll b/llvm/test/Transforms/MergeFunc/linkonce_odr.ll
index 1ad0d727f83..825f9054d7b 100644
--- a/llvm/test/Transforms/MergeFunc/linkonce_odr.ll
+++ b/llvm/test/Transforms/MergeFunc/linkonce_odr.ll
@@ -1,4 +1,4 @@
-; RUN: opt -S -mergefunc < %s | FileCheck %s
+; RUN: opt -S -mergefunc < %s | FileCheck %s -implicit-check-not=funC
 
 ; Replacments should be totally ordered on the function name.
 ; If we don't do this we  can end up with one module defining a thunk for @funA
@@ -15,6 +15,13 @@
 ; CHECK-NEXT:    tail call i32 @funA(i32 %0, i32 %1)
 ; CHECK-NEXT:    ret
 
+define linkonce_odr i32 @funC(i32 %x, i32 %y) {
+  %sum = add i32 %x, %y
+  %sum2 = add i32 %x, %sum
+  %sum3 = add i32 %x, %sum2
+  ret i32 %sum3
+}
+
 define linkonce_odr i32 @funB(i32 %x, i32 %y) {
   %sum = add i32 %x, %y
   %sum2 = add i32 %x, %sum
@@ -28,3 +35,8 @@ define linkonce_odr i32 @funA(i32 %x, i32 %y) {
   %sum3 = add i32 %x, %sum2
   ret i32 %sum3
 }
+
+; This creates a use of @funB, preventing -mergefunc from deleting it.
+; @funC, however, can safely be deleted as it has no uses, and is discardable
+; if unused.
+@take_addr_of_funB = global i8* bitcast (i32 (i32, i32)* @funB to i8*)