Reapply "Linker: Drop function pointers for overridden subprograms"

This reverts commit r233254, effectively reapplying r233164 (and its
successors), with an additional testcase for when subprograms match
exactly.  This fixes PR22792 (again).

I'm using the same approach, but I've moved up the call to
`stripReplacedSubprograms()`.  The function pointers need to be dropped
before mapping any metadata from the source module, or else this can
drop the function from new subprograms that have merged (via Metadata
uniquing) with the old ones.  Dropping the pointers first prevents them
from merging.

**** The original commit message follows. ****

Linker: Drop function pointers for overridden subprograms

Instead of dropping subprograms that have been overridden, just set
their function pointers to `nullptr`.  This is a minor adjustment to the
stop-gap fix for PR21910 committed in r224487, and fixes the crasher
from PR22792.

The problem that r224487 put a band-aid on: how do we find the canonical
subprogram for a `Function`?  Since the backend currently relies on
`DebugInfoFinder` (which does a naive in-order traversal of compile
units and picks the first subprogram) for this, r224487 tried dropping
non-canonical subprograms.

Dropping subprograms fails because the backend *also* builds up a map
from subprogram to compile unit (`DwarfDebug::SPMap`) based on the
subprogram lists.  A missing subprogram causes segfaults later when an
inlined reference (such as in this testcase) is created.

Instead, just drop the `Function` pointer to `nullptr`, which nicely
mirrors what happens when an already-inlined `Function` is optimized
out.  We can't really be sure that it's the same definition anyway, as
the testcase demonstrates.

This still isn't completely satisfactory.  Two flaws at least that I can
think of:

  - I still haven't found a straightforward way to make this symmetric
    in the IR.  (Interestingly, the DWARF output is already symmetric,
    and I've tested for that to be sure we don't regress.)
  - Using `DebugInfoFinder` to find the canonical subprogram for a
    function is kind of crazy.  We should just attach metadata to the
    function, like this:

        define weak i32 @foo(i32, i32) !dbg !MDSubprogram(...) {

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233302 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Linker/LinkModules.cpp b/lib/Linker/LinkModules.cpp
index d1000dc9a9f3a25f1e5ae19a61d6d61e82b1f0d8..21edc504080aef82a46a392ffe827777aee19402 100644 (file)
--- a/lib/Linker/LinkModules.cpp
+++ b/lib/Linker/LinkModules.cpp
@@ -1250,9 +1250,10 @@ void ModuleLinker::linkNamedMDNodes() {
 
 /// Drop DISubprograms that have been superseded.
 ///
-/// FIXME: this creates an asymmetric result: we strip losing subprograms from
-/// DstM, but leave losing subprograms in SrcM.  Instead we should also strip
-/// losers from SrcM, but this requires extra plumbing in MapMetadata.
+/// FIXME: this creates an asymmetric result: we strip functions from losing
+/// subprograms in DstM, but leave losing subprograms in SrcM.
+/// TODO: Remove this logic once the backend can correctly determine canonical
+/// subprograms.
 void ModuleLinker::stripReplacedSubprograms() {
   // Avoid quadratic runtime by returning early when there's nothing to do.
   if (OverridingFunctions.empty())
@@ -1262,8 +1263,8 @@ void ModuleLinker::stripReplacedSubprograms() {
   auto Functions = std::move(OverridingFunctions);
   OverridingFunctions.clear();
 
-  // Drop subprograms whose functions have been overridden by the new compile
-  // unit.
+  // Drop functions from subprograms if they've been overridden by the new
+  // compile unit.
   NamedMDNode *CompileUnits = DstM->getNamedMetadata("llvm.dbg.cu");
   if (!CompileUnits)
     return;
@@ -1274,19 +1275,15 @@ void ModuleLinker::stripReplacedSubprograms() {
     DITypedArray<DISubprogram> SPs(CU.getSubprograms());
     assert(SPs && "Expected valid subprogram array");
 
-    SmallVector<Metadata *, 16> NewSPs;
-    NewSPs.reserve(SPs.getNumElements());
     for (unsigned S = 0, SE = SPs.getNumElements(); S != SE; ++S) {
       DISubprogram SP = SPs.getElement(S);
-      if (SP && SP.getFunction() && Functions.count(SP.getFunction()))
+      if (!SP || !SP.getFunction() || !Functions.count(SP.getFunction()))
         continue;
 
-      NewSPs.push_back(SP);
+      // Prevent DebugInfoFinder from tagging this as the canonical subprogram,
+      // since the canonical one is in the incoming module.
+      SP->replaceFunction(nullptr);
     }
-
-    // Redirect operand to the overriding subprogram.
-    if (NewSPs.size() != SPs.getNumElements())
-      CU.replaceSubprograms(DIArray(MDNode::get(DstM->getContext(), NewSPs)));
   }
 }
 
@@ -1563,6 +1560,13 @@ bool ModuleLinker::run() {
     MapValue(GV, ValueMap, RF_None, &TypeMap, &ValMaterializer);
   }
 
+  // Strip replaced subprograms before mapping any metadata -- so that we're
+  // not changing metadata from the source module (note that
+  // linkGlobalValueBody() eventually calls RemapInstruction() and therefore
+  // MapMetadata()) -- but after linking global value protocols -- so that
+  // OverridingFunctions has been built.
+  stripReplacedSubprograms();
+
   // Link in the function bodies that are defined in the source module into
   // DstM.
   for (Function &SF : *SrcM) {
@@ -1585,9 +1589,6 @@ bool ModuleLinker::run() {
     linkGlobalValueBody(Src);
   }
 
-  // Strip replaced subprograms before linking together compile units.
-  stripReplacedSubprograms();
-
   // Remap all of the named MDNodes in Src into the DstM module. We do this
   // after linking GlobalValues so that MDNodes that reference GlobalValues
   // are properly remapped.

diff --git a/test/Linker/Inputs/subprogram-linkonce-weak-odr.ll b/test/Linker/Inputs/subprogram-linkonce-weak-odr.ll
new file mode 100644 (file)
index 0000000..b6518a8
--- /dev/null
+++ b/test/Linker/Inputs/subprogram-linkonce-weak-odr.ll
@@ -0,0 +1,15 @@
+define weak_odr i32 @foo(i32 %a, i32 %b) {
+entry:
+  %sum = add i32 %a, %b, !dbg !MDLocation(line: 2, scope: !3)
+  ret i32 %sum, !dbg !MDLocation(line: 3, scope: !3)
+}
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+
+!llvm.dbg.cu = !{!1}
+!1 = !MDCompileUnit(language: DW_LANG_C99, file: !2, subprograms: !{!3}, emissionKind: 1)
+!2 = !MDFile(filename: "foo.c", directory: "/path/to/dir")
+!3 = !MDSubprogram(file: !4, scope: !4, line: 1, name: "foo", function: i32 (i32, i32)* @foo, type: !5)
+!4 = !MDFile(filename: "foo.h", directory: "/path/to/dir")
+!5 = !MDSubroutineType(types: !{})

diff --git a/test/Linker/Inputs/subprogram-linkonce-weak.ll b/test/Linker/Inputs/subprogram-linkonce-weak.ll
new file mode 100644 (file)
index 0000000..e73143d
--- /dev/null
+++ b/test/Linker/Inputs/subprogram-linkonce-weak.ll
@@ -0,0 +1,16 @@
+define weak i32 @foo(i32 %a, i32 %b) {
+entry:
+  %sum = call i32 @fastadd(i32 %a, i32 %b), !dbg !MDLocation(line: 52, scope: !3)
+  ret i32 %sum, !dbg !MDLocation(line: 53, scope: !3)
+}
+
+declare i32 @fastadd(i32, i32)
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+
+!llvm.dbg.cu = !{!1}
+!1 = !MDCompileUnit(language: DW_LANG_C99, file: !2, subprograms: !{!3}, emissionKind: 1)
+!2 = !MDFile(filename: "foo.c", directory: "/path/to/dir")
+!3 = !MDSubprogram(file: !2, scope: !2, line: 51, name: "foo", function: i32 (i32, i32)* @foo, type: !4)
+!4 = !MDSubroutineType(types: !{})

diff --git a/test/Linker/replaced-function-matches-first-subprogram.ll b/test/Linker/replaced-function-matches-first-subprogram.ll
index 508e28da565905fe315ee33b2eed5db62694208b..ac6633d1c018a807f03986d9195a8b4640884ba9 100644 (file)
--- a/test/Linker/replaced-function-matches-first-subprogram.ll
+++ b/test/Linker/replaced-function-matches-first-subprogram.ll
@@ -45,9 +45,9 @@ entry:
 !1 = !MDFile(filename: "t1.cpp", directory: "/Users/dexonsmith/data/llvm/staging/test/Linker/repro/d1")
 !2 = !{}
 
-; Extract out each compile unit's single subprogram.  The replaced subprogram
-; should be dropped by the first compile unit.
-; CHECK-DAG: ![[SPs1]] = !{![[SP1:[0-9]+]]}
+; Extract out each compile unit's single subprogram.  The replaced subprogram's
+; function should drop to null in the first compile unit.
+; CHECK-DAG: ![[SPs1]] = !{![[SP1:[0-9]+]], ![[SP2r:[0-9]+]]}
 ; CHECK-DAG: ![[SPs2]] = !{![[SP2:[0-9]+]]}
 !3 = !{!4, !7}
 !4 = !MDSubprogram(name: "foo", line: 2, isLocal: false, isDefinition: true, flags: DIFlagPrototyped, isOptimized: false, scopeLine: 2, file: !1, scope: !5, type: !6, function: i32 ()* @_Z3foov, variables: !2)
@@ -58,6 +58,10 @@ entry:
 ; subprogram is pointing at the correct function.
 ; CHECK-DAG: ![[SP1]] = !MDSubprogram({{.*}} function: i32 ()* @_Z3foov
 ; CHECK-DAG: ![[SP2]] = !MDSubprogram({{.*}} file: ![[FILE:[0-9]+]],{{.*}} function: i32 (%struct.Class*)* @_ZN5ClassIiE3fooEv
+
+; We can't use CHECK-NOT/CHECK-SAME with a CHECK-DAG, so rely on field order to
+; prove that there's no function: here.
+; CHECK-DAG: ![[SP2r]] = {{.*}}!MDSubprogram({{.*}} isOptimized: false, variables:
 !7 = !MDSubprogram(name: "foo", line: 2, isLocal: false, isDefinition: true, flags: DIFlagPrototyped, isOptimized: false, scopeLine: 2, file: !8, scope: !9, type: !6, function: i32 (%struct.Class*)* @_ZN5ClassIiE3fooEv, variables: !2)
 
 ; The new subprogram should be pointing at the new directory.

diff --git a/test/Linker/subprogram-linkonce-weak-odr.ll b/test/Linker/subprogram-linkonce-weak-odr.ll
new file mode 100644 (file)
index 0000000..97058fd
--- /dev/null
+++ b/test/Linker/subprogram-linkonce-weak-odr.ll
@@ -0,0 +1,177 @@
+; RUN: llvm-link %s %S/Inputs/subprogram-linkonce-weak-odr.ll -S -o %t1
+; RUN: FileCheck %s -check-prefix=LW -check-prefix=CHECK <%t1
+; RUN: llvm-link %S/Inputs/subprogram-linkonce-weak-odr.ll %s -S -o %t2
+; RUN: FileCheck %s -check-prefix=WL -check-prefix=CHECK <%t2
+
+; This testcase tests the following flow:
+;  - File A defines a linkonce_odr version of @foo which has inlined into @bar.
+;  - File B defines a weak_odr version of @foo (identical definition).
+;  - Linkage rules state File B version of @foo wins.
+;  - Debug info for the subprograms of @foo match exactly.  Without
+;    intervention, the same subprogram would show up in both compile units, and
+;    it would get associated with the compile unit where it was linkonce.
+;  - @bar has inlined debug info related to the linkonce_odr @foo.
+;
+; This checks a corner case for the fix for PR22792, where subprograms match
+; exactly.  It's a companion for subprogram-linkonce-weak.ll.
+
+; The LW prefix means linkonce (this file) first, then weak (the other file).
+; The WL prefix means weak (the other file) first, then linkonce (this file).
+
+; We'll see @bar before @foo if this file is first.
+; LW-LABEL: define i32 @bar(
+; LW: %sum = add i32 %a, %b, !dbg ![[FOOINBAR:[0-9]+]]
+; LW: ret i32 %sum, !dbg ![[BARRET:[0-9]+]]
+; LW-LABEL: define weak_odr i32 @foo(
+; LW: %sum = add i32 %a, %b, !dbg ![[FOOADD:[0-9]+]]
+; LW: ret i32 %sum, !dbg ![[FOORET:[0-9]+]]
+
+; We'll see @foo before @bar if this file is second.
+; WL-LABEL: define weak_odr i32 @foo(
+; WL: %sum = add i32 %a, %b, !dbg ![[FOOADD:[0-9]+]]
+; WL: ret i32 %sum, !dbg ![[FOORET:[0-9]+]]
+; WL-LABEL: define i32 @bar(
+; WL: %sum = add i32 %a, %b, !dbg ![[FOOINBAR:[0-9]+]]
+; WL: ret i32 %sum, !dbg ![[BARRET:[0-9]+]]
+
+define i32 @bar(i32 %a, i32 %b) {
+entry:
+  %sum = add i32 %a, %b, !dbg !MDLocation(line: 2, scope: !4,
+                                          inlinedAt: !MDLocation(line: 12, scope: !3))
+  ret i32 %sum, !dbg !MDLocation(line: 13, scope: !3)
+}
+
+define linkonce_odr i32 @foo(i32 %a, i32 %b) {
+entry:
+  %sum = add i32 %a, %b, !dbg !MDLocation(line: 2, scope: !4)
+  ret i32 %sum, !dbg !MDLocation(line: 3, scope: !4)
+}
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+
+; CHECK-LABEL: !llvm.dbg.cu =
+; LW-SAME: !{![[LCU:[0-9]+]], ![[WCU:[0-9]+]]}
+; WL-SAME: !{![[WCU:[0-9]+]], ![[LCU:[0-9]+]]}
+!llvm.dbg.cu = !{!1}
+
+; LW: ![[LCU]] = !MDCompileUnit({{.*}} subprograms: ![[LSPs:[0-9]+]]
+; LW: ![[LSPs]] = !{![[BARSP:[0-9]+]], ![[FOOSP:[0-9]+]]}
+; LW: ![[BARSP]] = !MDSubprogram(name: "bar",
+; LW-SAME: function: i32 (i32, i32)* @bar
+; LW: ![[FOOSP]] = {{.*}}!MDSubprogram(name: "foo",
+; LW-NOT: function:
+; LW-SAME: ){{$}}
+; LW: ![[WCU]] = !MDCompileUnit({{.*}} subprograms: ![[WSPs:[0-9]+]]
+; LW: ![[WSPs]] = !{![[WEAKFOOSP:[0-9]+]]}
+; LW: ![[WEAKFOOSP]] = !MDSubprogram(name: "foo",
+; LW-SAME: function: i32 (i32, i32)* @foo
+; LW: ![[FOOINBAR]] = !MDLocation(line: 2, scope: ![[FOOSP]], inlinedAt: ![[BARIA:[0-9]+]])
+; LW: ![[BARIA]] = !MDLocation(line: 12, scope: ![[BARSP]])
+; LW: ![[BARRET]] = !MDLocation(line: 13, scope: ![[BARSP]])
+; LW: ![[FOOADD]] = !MDLocation(line: 2, scope: ![[WEAKFOOSP]])
+; LW: ![[FOORET]] = !MDLocation(line: 3, scope: ![[WEAKFOOSP]])
+
+; Same as above, but reordered.
+; WL: ![[WCU]] = !MDCompileUnit({{.*}} subprograms: ![[WSPs:[0-9]+]]
+; WL: ![[WSPs]] = !{![[WEAKFOOSP:[0-9]+]]}
+; WL: ![[WEAKFOOSP]] = !MDSubprogram(name: "foo",
+; WL-SAME: function: i32 (i32, i32)* @foo
+; WL: ![[LCU]] = !MDCompileUnit({{.*}} subprograms: ![[LSPs:[0-9]+]]
+; Note: for symmetry, LSPs would have a different copy of the subprogram.
+; WL: ![[LSPs]] = !{![[BARSP:[0-9]+]], ![[WEAKFOOSP:[0-9]+]]}
+; WL: ![[BARSP]] = !MDSubprogram(name: "bar",
+; WL-SAME: function: i32 (i32, i32)* @bar
+; WL: ![[FOOADD]] = !MDLocation(line: 2, scope: ![[WEAKFOOSP]])
+; WL: ![[FOORET]] = !MDLocation(line: 3, scope: ![[WEAKFOOSP]])
+; WL: ![[FOOINBAR]] = !MDLocation(line: 2, scope: ![[WEAKFOOSP]], inlinedAt: ![[BARIA:[0-9]+]])
+; WL: ![[BARIA]] = !MDLocation(line: 12, scope: ![[BARSP]])
+; WL: ![[BARRET]] = !MDLocation(line: 13, scope: ![[BARSP]])
+
+!1 = !MDCompileUnit(language: DW_LANG_C99, file: !2, subprograms: !{!3, !4}, emissionKind: 1)
+!2 = !MDFile(filename: "bar.c", directory: "/path/to/dir")
+!3 = !MDSubprogram(file: !2, scope: !2, line: 11, name: "bar", function: i32 (i32, i32)* @bar, type: !6)
+!4 = !MDSubprogram(file: !5, scope: !5, line: 1, name: "foo", function: i32 (i32, i32)* @foo, type: !6)
+!5 = !MDFile(filename: "foo.h", directory: "/path/to/dir")
+!6 = !MDSubroutineType(types: !{})
+
+; Crasher for llc.
+; REQUIRES: object-emission
+; RUN: %llc_dwarf -filetype=obj -O0 %t1 -o %t1.o
+; RUN: llvm-dwarfdump %t1.o -debug-dump=all | FileCheck %s -check-prefix=DWLW -check-prefix=DW
+; RUN: %llc_dwarf -filetype=obj -O0 %t2 -o %t2.o
+; RUN: llvm-dwarfdump %t2.o -debug-dump=all | FileCheck %s -check-prefix=DWWL -check-prefix=DW
+; Check that the debug info puts the subprogram (with PCs) in the correct
+; compile unit.
+
+; DW-LABEL: .debug_info contents:
+; DWLW:     DW_TAG_compile_unit
+; DWLW:       DW_AT_name {{.*}}"bar.c"
+; Note: If we stop emitting foo here, the comment below for DWWL (and the
+; check) should be copied up here.
+; DWLW:       DW_TAG_subprogram
+; DWLW-NOT:     DW_AT_low_pc
+; DWLW-NOT:     DW_AT_high_pc
+; DWLW:         DW_AT_name {{.*}}foo
+; DWLW:         DW_AT_decl_file {{.*}}"/path/to/dir/foo.h"
+; DWLW:         DW_AT_decl_line {{.*}}(1)
+; DWLW:       DW_TAG_subprogram
+; DWLW:         DW_AT_low_pc
+; DWLW:         DW_AT_high_pc
+; DWLW:         DW_AT_name {{.*}}bar
+; DWLW:         DW_AT_decl_file {{.*}}"/path/to/dir/bar.c"
+; DWLW:         DW_AT_decl_line {{.*}}(11)
+; DWLW:         DW_TAG_inlined_subroutine
+; DWLW:           DW_AT_abstract_origin
+; DWLW:     DW_TAG_compile_unit
+; DWLW:       DW_AT_name {{.*}}"foo.c"
+; DWLW:       DW_TAG_subprogram
+; DWLW:         DW_AT_low_pc
+; DWLW:         DW_AT_high_pc
+; DWLW:         DW_AT_name {{.*}}foo
+; DWLW:         DW_AT_decl_file {{.*}}"/path/to/dir/foo.h"
+; DWLW:         DW_AT_decl_line {{.*}}(1)
+
+; The DWARF output is already symmetric (just reordered).
+; DWWL:     DW_TAG_compile_unit
+; DWWL:       DW_AT_name {{.*}}"foo.c"
+; DWWL:       DW_TAG_subprogram
+; DWWL:         DW_AT_low_pc
+; DWWL:         DW_AT_high_pc
+; DWWL:         DW_AT_name {{.*}}foo
+; DWWL:         DW_AT_decl_file {{.*}}"/path/to/dir/foo.h"
+; DWWL:         DW_AT_decl_line {{.*}}(1)
+; DWWL:     DW_TAG_compile_unit
+; DWWL:       DW_AT_name {{.*}}"bar.c"
+; Note: for symmetry, foo would also show up in this compile unit
+; (alternatively, it wouldn't show up in the DWLW case).  If we start emitting
+; foo here, this should be updated by checking that we don't emit low_pc and
+; high_pc for it.
+; DWWL-NOT:     DW_AT_name {{.*}}foo
+; DWWL:       DW_TAG_subprogram
+; DWWL-NOT:     DW_AT_name {{.*}}foo
+; DWWL:         DW_AT_low_pc
+; DWWL:         DW_AT_high_pc
+; DWWL-NOT:     DW_AT_name {{.*}}foo
+; DWWL:         DW_AT_name {{.*}}bar
+; DWWL:         DW_AT_decl_file {{.*}}"/path/to/dir/bar.c"
+; DWWL:         DW_AT_decl_line {{.*}}(11)
+; DWWL:         DW_TAG_inlined_subroutine
+; DWWL:           DW_AT_abstract_origin
+
+; DW-LABEL:   .debug_line contents:
+; Check that we have the right things in the line table as well.
+
+; DWLW-LABEL: file_names[{{ *}}1]{{.*}} bar.c
+; DWLW-LABEL: file_names[{{ *}}2]{{.*}} foo.h
+; DWLW:        2 0 2 0 0 is_stmt prologue_end
+; DWLW-LABEL: file_names[{{ *}}1]{{.*}} foo.h
+; DWLW:        2 0 1 0 0 is_stmt prologue_end
+; DWLW-NOT:                      prologue_end
+
+; DWWL-LABEL: file_names[{{ *}}1]{{.*}} foo.h
+; DWWL:        2 0 1 0 0 is_stmt prologue_end
+; DWWL-LABEL: file_names[{{ *}}1]{{.*}} bar.c
+; DWWL-LABEL: file_names[{{ *}}2]{{.*}} foo.h
+; DWWL:        2 0 2 0 0 is_stmt prologue_end
+; DWWL-NOT:                      prologue_end

diff --git a/test/Linker/subprogram-linkonce-weak.ll b/test/Linker/subprogram-linkonce-weak.ll
new file mode 100644 (file)
index 0000000..42a8b39
--- /dev/null
+++ b/test/Linker/subprogram-linkonce-weak.ll
@@ -0,0 +1,171 @@
+; RUN: llvm-link %s %S/Inputs/subprogram-linkonce-weak.ll -S -o %t1
+; RUN: FileCheck %s -check-prefix=LW -check-prefix=CHECK <%t1
+; RUN: llvm-link %S/Inputs/subprogram-linkonce-weak.ll %s -S -o %t2
+; RUN: FileCheck %s -check-prefix=WL -check-prefix=CHECK <%t2
+
+; This testcase tests the following flow:
+;  - File A defines a linkonce version of @foo which has inlined into @bar.
+;  - File B defines a weak version of @foo (different definition).
+;  - Linkage rules state File B version of @foo wins.
+;  - @bar still has inlined debug info related to the linkonce @foo.
+;
+; This should fix PR22792, although the testcase was hand-written.  There's a
+; RUN line with a crasher for llc at the end with checks for the DWARF output.
+
+; The LW prefix means linkonce (this file) first, then weak (the other file).
+; The WL prefix means weak (the other file) first, then linkonce (this file).
+
+; We'll see @bar before @foo if this file is first.
+; LW-LABEL: define i32 @bar(
+; LW: %sum = add i32 %a, %b, !dbg ![[FOOINBAR:[0-9]+]]
+; LW: ret i32 %sum, !dbg ![[BARRET:[0-9]+]]
+; LW-LABEL: define weak i32 @foo(
+; LW: %sum = call i32 @fastadd(i32 %a, i32 %b), !dbg ![[FOOCALL:[0-9]+]]
+; LW: ret i32 %sum, !dbg ![[FOORET:[0-9]+]]
+
+; We'll see @foo before @bar if this file is second.
+; WL-LABEL: define weak i32 @foo(
+; WL: %sum = call i32 @fastadd(i32 %a, i32 %b), !dbg ![[FOOCALL:[0-9]+]]
+; WL: ret i32 %sum, !dbg ![[FOORET:[0-9]+]]
+; WL-LABEL: define i32 @bar(
+; WL: %sum = add i32 %a, %b, !dbg ![[FOOINBAR:[0-9]+]]
+; WL: ret i32 %sum, !dbg ![[BARRET:[0-9]+]]
+
+define i32 @bar(i32 %a, i32 %b) {
+entry:
+  %sum = add i32 %a, %b, !dbg !MDLocation(line: 2, scope: !4,
+                                          inlinedAt: !MDLocation(line: 12, scope: !3))
+  ret i32 %sum, !dbg !MDLocation(line: 13, scope: !3)
+}
+
+define linkonce i32 @foo(i32 %a, i32 %b) {
+entry:
+  %sum = add i32 %a, %b, !dbg !MDLocation(line: 2, scope: !4)
+  ret i32 %sum, !dbg !MDLocation(line: 3, scope: !4)
+}
+
+!llvm.module.flags = !{!0}
+!0 = !{i32 2, !"Debug Info Version", i32 3}
+
+; CHECK-LABEL: !llvm.dbg.cu =
+; LW-SAME: !{![[LCU:[0-9]+]], ![[WCU:[0-9]+]]}
+; WL-SAME: !{![[WCU:[0-9]+]], ![[LCU:[0-9]+]]}
+!llvm.dbg.cu = !{!1}
+
+; LW: ![[LCU]] = !MDCompileUnit({{.*}} subprograms: ![[LSPs:[0-9]+]]
+; LW: ![[LSPs]] = !{![[BARSP:[0-9]+]], ![[FOOSP:[0-9]+]]}
+; LW: ![[BARSP]] = !MDSubprogram(name: "bar",
+; LW-SAME: function: i32 (i32, i32)* @bar
+; LW: ![[FOOSP]] = {{.*}}!MDSubprogram(name: "foo",
+; LW-NOT: function:
+; LW-SAME: ){{$}}
+; LW: ![[WCU]] = !MDCompileUnit({{.*}} subprograms: ![[WSPs:[0-9]+]]
+; LW: ![[WSPs]] = !{![[WEAKFOOSP:[0-9]+]]}
+; LW: ![[WEAKFOOSP]] = !MDSubprogram(name: "foo",
+; LW-SAME: function: i32 (i32, i32)* @foo
+; LW: ![[FOOINBAR]] = !MDLocation(line: 2, scope: ![[FOOSP]], inlinedAt: ![[BARIA:[0-9]+]])
+; LW: ![[BARIA]] = !MDLocation(line: 12, scope: ![[BARSP]])
+; LW: ![[BARRET]] = !MDLocation(line: 13, scope: ![[BARSP]])
+; LW: ![[FOOCALL]] = !MDLocation(line: 52, scope: ![[WEAKFOOSP]])
+; LW: ![[FOORET]] = !MDLocation(line: 53, scope: ![[WEAKFOOSP]])
+
+; Same as above, but reordered.
+; WL: ![[WCU]] = !MDCompileUnit({{.*}} subprograms: ![[WSPs:[0-9]+]]
+; WL: ![[WSPs]] = !{![[WEAKFOOSP:[0-9]+]]}
+; WL: ![[WEAKFOOSP]] = !MDSubprogram(name: "foo",
+; WL-SAME: function: i32 (i32, i32)* @foo
+; WL: ![[LCU]] = !MDCompileUnit({{.*}} subprograms: ![[LSPs:[0-9]+]]
+; WL: ![[LSPs]] = !{![[BARSP:[0-9]+]], ![[FOOSP:[0-9]+]]}
+; WL: ![[BARSP]] = !MDSubprogram(name: "bar",
+; WL-SAME: function: i32 (i32, i32)* @bar
+; WL: ![[FOOSP]] = {{.*}}!MDSubprogram(name: "foo",
+; Note, for symmetry, this should be "NOT: function:" and "SAME: ){{$}}".
+; WL-SAME: function: i32 (i32, i32)* @foo
+; WL: ![[FOOCALL]] = !MDLocation(line: 52, scope: ![[WEAKFOOSP]])
+; WL: ![[FOORET]] = !MDLocation(line: 53, scope: ![[WEAKFOOSP]])
+; WL: ![[FOOINBAR]] = !MDLocation(line: 2, scope: ![[FOOSP]], inlinedAt: ![[BARIA:[0-9]+]])
+; WL: ![[BARIA]] = !MDLocation(line: 12, scope: ![[BARSP]])
+; WL: ![[BARRET]] = !MDLocation(line: 13, scope: ![[BARSP]])
+
+!1 = !MDCompileUnit(language: DW_LANG_C99, file: !2, subprograms: !{!3, !4}, emissionKind: 1)
+!2 = !MDFile(filename: "bar.c", directory: "/path/to/dir")
+!3 = !MDSubprogram(file: !2, scope: !2, line: 11, name: "bar", function: i32 (i32, i32)* @bar, type: !5)
+!4 = !MDSubprogram(file: !2, scope: !2, line: 1, name: "foo", function: i32 (i32, i32)* @foo, type: !5)
+!5 = !MDSubroutineType(types: !{})
+
+; Crasher for llc.
+; REQUIRES: object-emission
+; RUN: %llc_dwarf -filetype=obj -O0 %t1 -o %t1.o
+; RUN: llvm-dwarfdump %t1.o -debug-dump=all | FileCheck %s -check-prefix=DWLW -check-prefix=DW
+; RUN: %llc_dwarf -filetype=obj -O0 %t2 -o %t2.o
+; RUN: llvm-dwarfdump %t2.o -debug-dump=all | FileCheck %s -check-prefix=DWWL -check-prefix=DW
+; Check that the debug info for the discarded linkonce version of @foo doesn't
+; reference any code, and that the other subprograms look correct.
+
+; DW-LABEL: .debug_info contents:
+; DWLW:     DW_TAG_compile_unit
+; DWLW:       DW_AT_name {{.*}}"bar.c"
+; DWLW:       DW_TAG_subprogram
+; DWLW-NOT:     DW_AT_low_pc
+; DWLW-NOT:     DW_AT_high_pc
+; DWLW:         DW_AT_name {{.*}}foo
+; DWLW:         DW_AT_decl_file {{.*}}"/path/to/dir/bar.c"
+; DWLW:         DW_AT_decl_line {{.*}}(1)
+; DWLW:       DW_TAG_subprogram
+; DWLW:         DW_AT_low_pc
+; DWLW:         DW_AT_high_pc
+; DWLW:         DW_AT_name {{.*}}bar
+; DWLW:         DW_AT_decl_file {{.*}}"/path/to/dir/bar.c"
+; DWLW:         DW_AT_decl_line {{.*}}(11)
+
+; DWLW:         DW_TAG_inlined_subroutine
+; DWLW:           DW_AT_abstract_origin
+; DWLW:     DW_TAG_compile_unit
+; DWLW:       DW_AT_name {{.*}}"foo.c"
+; DWLW:       DW_TAG_subprogram
+; DWLW:         DW_AT_low_pc
+; DWLW:         DW_AT_high_pc
+; DWLW:         DW_AT_name {{.*}}foo
+; DWLW:         DW_AT_decl_file {{.*}}"/path/to/dir/foo.c"
+; DWLW:         DW_AT_decl_line {{.*}}(51)
+
+; The DWARF output is already symmetric (just reordered).
+; DWWL:     DW_TAG_compile_unit
+; DWWL:       DW_AT_name {{.*}}"foo.c"
+; DWWL:       DW_TAG_subprogram
+; DWWL:         DW_AT_low_pc
+; DWWL:         DW_AT_high_pc
+; DWWL:         DW_AT_name {{.*}}foo
+; DWWL:         DW_AT_decl_file {{.*}}"/path/to/dir/foo.c"
+; DWWL:         DW_AT_decl_line {{.*}}(51)
+; DWWL:     DW_TAG_compile_unit
+; DWWL:       DW_AT_name {{.*}}"bar.c"
+; DWWL:       DW_TAG_subprogram
+; DWWL-NOT:     DW_AT_low_pc
+; DWWL-NOT:     DW_AT_high_pc
+; DWWL:         DW_AT_name {{.*}}foo
+; DWWL:         DW_AT_decl_file {{.*}}"/path/to/dir/bar.c"
+; DWWL:         DW_AT_decl_line {{.*}}(1)
+; DWWL:       DW_TAG_subprogram
+; DWWL:         DW_AT_low_pc
+; DWWL:         DW_AT_high_pc
+; DWWL:         DW_AT_name {{.*}}bar
+; DWWL:         DW_AT_decl_file {{.*}}"/path/to/dir/bar.c"
+; DWWL:         DW_AT_decl_line {{.*}}(11)
+; DWWL:         DW_TAG_inlined_subroutine
+; DWWL:           DW_AT_abstract_origin
+
+; DW-LABEL:   .debug_line contents:
+; Check that we have the right things in the line table as well.
+
+; DWLW-LABEL: file_names[{{ *}}1]{{.*}} bar.c
+; DWLW:        2 0 1 0 0 is_stmt prologue_end
+; DWLW-LABEL: file_names[{{ *}}1]{{.*}} foo.c
+; DWLW:       52 0 1 0 0 is_stmt prologue_end
+; DWLW-NOT:                      prologue_end
+
+; DWWL-LABEL: file_names[{{ *}}1]{{.*}} foo.c
+; DWWL:       52 0 1 0 0 is_stmt prologue_end
+; DWWL-LABEL: file_names[{{ *}}1]{{.*}} bar.c
+; DWWL:        2 0 1 0 0 is_stmt prologue_end
+; DWWL-NOT:                      prologue_end