Reapply "Linker: Drop superseded subprograms"

This reverts commit r224416, reapplying r224389.  The buildbots hadn't
recovered after my revert, waiting until David reverted a couple of his
commits.  It looks like it was just bad timing (where we were both
modifying code related to the same assertion).  Trying again...

Here's the original text:

    When a function gets replaced by `ModuleLinker`, drop superseded
    subprograms.  This ensures that the "first" subprogram pointing at a
    function is the same one that `!dbg` references point at.

    This is a stop-gap fix for PR21910.  Notably, this fixes Release+Asserts
    bootstraps that are currently asserting out in
    `LexicalScopes::initialize()` due to the explicit instantiations in
    `lib/IR/Dominators.cpp` eventually getting replaced by -argpromotion.

llvm-svn: 224487

1 files changed, 27 insertions, 0 deletions

diff --git a/llvm/test/Linker/Inputs/replaced-function-matches-first-subprogram.ll b/llvm/test/Linker/Inputs/replaced-function-matches-first-subprogram.ll
new file mode 100644
index 00000000000..fb7b634e66a
--- /dev/null
+++ b/llvm/test/Linker/Inputs/replaced-function-matches-first-subprogram.ll
@@ -0,0 +1,27 @@
+%struct.Class = type { i8 }
+
+define weak_odr i32 @_ZN5ClassIiE3fooEv(%struct.Class* %this) align 2 {
+entry:
+  %this.addr = alloca %struct.Class*, align 8
+  store %struct.Class* %this, %struct.Class** %this.addr, align 8
+  %this1 = load %struct.Class** %this.addr
+  ret i32 0, !dbg !12
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!8, !9, !10}
+!llvm.ident = !{!11}
+
+!0 = !{!"0x11\004\00clang version 3.6.0 (trunk 224193) (llvm/trunk 224197)\000\00\000\00\002", !1, !2, !2, !3, !2, !2} ; [ DW_TAG_compile_unit ] [/Users/dexonsmith/data/llvm/staging/test/Linker/repro/d2/t2.cpp] [DW_LANG_C_plus_plus]
+!1 = !{!"t2.cpp", !"/Users/dexonsmith/data/llvm/staging/test/Linker/repro/d2"}
+!2 = !{}
+!3 = !{!4}
+!4 = !{!"0x2e\00foo\00foo\00\002\000\001\000\000\00256\000\002", !5, !6, !7, null, i32 (%struct.Class*)* @_ZN5ClassIiE3fooEv, null, null, !2} ; [ DW_TAG_subprogram ] [line 2] [def] [foo]
+!5 = !{!"../t.h", !"/Users/dexonsmith/data/llvm/staging/test/Linker/repro/d2"}
+!6 = !{!"0x29", !5}    ; [ DW_TAG_file_type ] [/Users/dexonsmith/data/llvm/staging/test/Linker/repro/d2/../t.h]
+!7 = !{!"0x15\00\000\000\000\000\000\000", null, null, null, !2, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!8 = !{i32 2, !"Dwarf Version", i32 2}
+!9 = !{i32 2, !"Debug Info Version", i32 2}
+!10 = !{i32 1, !"PIC Level", i32 2}
+!11 = !{!"clang version 3.6.0 (trunk 224193) (llvm/trunk 224197)"}
+!12 = !{i32 2, i32 15, !4, null}