[MergeFunc] Add linkonce test with discardable functions.

Author: fhahn

llvm/test/Transforms/MergeFunc/linkonce.ll

@@ -0,0 +1,56 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals all --include-generated-funcs --version 5
+; RUN: opt -S -passes=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
+; and another module defining a thunk for @funB.
+; The problem with this is that the linker could then choose these two stubs
+; each of the two modules and we end up with two stubs calling each other.
+
+define linkonce 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 i32 @funB(i32 %x, i32 %y) {
+  %sum = add i32 %x, %y
+  %sum2 = add i32 %x, %sum
+  %sum3 = add i32 %x, %sum2
+  ret i32 %sum3
+}
+
+define linkonce i32 @funA(i32 %x, i32 %y) {
+  %sum = add i32 %x, %y
+  %sum2 = add i32 %x, %sum
+  %sum3 = add i32 %x, %sum2
+  ret i32 %sum3
+}
+
+; This creates a use of @funB, preventing -passes=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 ptr @funB
+;.
+; CHECK: @take_addr_of_funB = global ptr @funB
+;.
+; CHECK-LABEL: define private i32 @0(
+; CHECK-SAME: i32 [[X:%.*]], i32 [[Y:%.*]]) {
+; CHECK-NEXT:    [[SUM:%.*]] = add i32 [[X]], [[Y]]
+; CHECK-NEXT:    [[SUM2:%.*]] = add i32 [[X]], [[SUM]]
+; CHECK-NEXT:    [[SUM3:%.*]] = add i32 [[X]], [[SUM2]]
+; CHECK-NEXT:    ret i32 [[SUM3]]
+;
+;
+; CHECK-LABEL: define linkonce i32 @funC(
+; CHECK-SAME: i32 [[TMP0:%.*]], i32 [[TMP1:%.*]]) {
+; CHECK-NEXT:    [[TMP3:%.*]] = tail call i32 @[[GLOB0:[0-9]+]](i32 [[TMP0]], i32 [[TMP1]])
+; CHECK-NEXT:    ret i32 [[TMP3]]
+;
+;
+; CHECK-LABEL: define linkonce i32 @funB(
+; CHECK-SAME: i32 [[TMP0:%.*]], i32 [[TMP1:%.*]]) {
+; CHECK-NEXT:    [[TMP3:%.*]] = tail call i32 @[[GLOB0]](i32 [[TMP0]], i32 [[TMP1]])
+; CHECK-NEXT:    ret i32 [[TMP3]]
+;