[MergeFuncs] Call removeUsers() prior to unnamed_addr RAUW

Summary:
For unnamed_addr functions we RAUW instead of only replacing direct callers. However, functions in which replacements were performed currently are not added back to the worklist, resulting in missed merging opportunities.

Fix this by calling removeUsers() prior to RAUW.

Reviewers: jfb, whitequark

Reviewed By: whitequark

Subscribers: rkruppe, llvm-commits

Differential Revision: https://reviews.llvm.org/D53262

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346385 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/IPO/MergeFunctions.cpp

@@ -770,6 +770,7 @@ void MergeFunctions::mergeTwoFunctions(Function *F, Function *G) {
         GlobalNumbers.erase(G);
         // If G's address is not significant, replace it entirely.
         Constant *BitcastF = ConstantExpr::getBitCast(F, G->getType());
+        removeUsers(G);
         G->replaceAllUsesWith(BitcastF);
       } else {
         // Redirect direct callers of G to F. (See note on MergeFunctionsPDI

test/Transforms/MergeFunc/unnamed-addr-reprocessing.ll

@@ -0,0 +1,35 @@
+; RUN: opt -S -mergefunc < %s | FileCheck %s
+
+; After test3 and test4 have been merged, we should detect that
+; test1 and test2 can also be merged.
+
+; CHECK: define void @test4() unnamed_addr
+; CHECK-NEXT: tail call void @test3()
+; CHECK: define void @test2() unnamed_addr
+; CHECK-NEXT: tail call void @test1()
+
+declare void @dummy()
+
+define void @test1() unnamed_addr {
+    call void @test3()
+    call void @test3()
+    ret void
+}
+
+define void @test2() unnamed_addr {
+    call void @test4()
+    call void @test4()
+    ret void
+}
+
+define void @test3() unnamed_addr {
+    call void @dummy()
+    call void @dummy()
+    ret void
+}
+
+define void @test4() unnamed_addr {
+    call void @dummy()
+    call void @dummy()
+    ret void
+}