[llvm] r350939 - [MergeFunc] Erase unused duplicate functions if they are discardable

[Vedant Kumar via llvm-commits]

Author: vedantk
Date: Fri Jan 11 09:56:35 2019
New Revision: 350939

URL: http://llvm.org/viewvc/llvm-project?rev=350939&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp
    llvm/trunk/test/Transforms/MergeFunc/linkonce_odr.ll

Modified: llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp?rev=350939&r1=350938&r2=350939&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp (original)
+++ llvm/trunk/lib/Transforms/IPO/MergeFunctions.cpp Fri Jan 11 09:56:35 2019
@@ -845,7 +845,7 @@ void MergeFunctions::mergeTwoFunctions(F
     // 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;

Modified: llvm/trunk/test/Transforms/MergeFunc/linkonce_odr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/MergeFunc/linkonce_odr.ll?rev=350939&r1=350938&r2=350939&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/MergeFunc/linkonce_odr.ll (original)
+++ llvm/trunk/test/Transforms/MergeFunc/linkonce_odr.ll Fri Jan 11 09:56:35 2019
@@ -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, i3
   %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.
+ at take_addr_of_funB = global i8* bitcast (i32 (i32, i32)* @funB to i8*)