Ensure ModuleLinker materializes complete comdat groups

Summary:
The module linker lazy links some "discardable if unused" global
values (e.g. linkonce), materializing and linking them only
if they are referenced in the module. If a comdat group contains a
linkonce member that is not referenced, however, it would not be
materialized and linked, leading to an incomplete comdat group.

If there are other object files not part of the same LTO link that also
define and use that comdat group, the linker may select the incomplete
group leading to link time unsats.

To solve this, whenever a global value body is linked, make sure we
materialize any other members of the same comdat group that are not yet
materialized. This ensures they are in the lazy link list and get linked
as well.

Added new test and adjusted old test to remove parts that didn't
make sense with fix.

Reviewers: rafael

Subscribers: dexonsmith, davidxl, llvm-commits

Differential Revision: http://reviews.llvm.org/D14516

llvm-svn: 252647

3 files changed, 21 insertions, 16 deletions

diff --git a/llvm/test/Linker/Inputs/only-needed-named-metadata.ll b/llvm/test/Linker/Inputs/only-needed-named-metadata.ll
index 95151692d3b..fa7bc2e3cc8 100644
--- a/llvm/test/Linker/Inputs/only-needed-named-metadata.ll
+++ b/llvm/test/Linker/Inputs/only-needed-named-metadata.ll
@@ -2,11 +2,8 @@
 
 declare i32 @foo()
 
-declare void @c1_a()
-
 define void @bar() {
 	load i32, i32* @X
 	call i32 @foo()
-	call void @c1_a()
 	ret void
 }
diff --git a/llvm/test/Linker/comdat_group.ll b/llvm/test/Linker/comdat_group.ll
new file mode 100644
index 00000000000..efaa94f2858
--- /dev/null
+++ b/llvm/test/Linker/comdat_group.ll
@@ -0,0 +1,20 @@
+; RUN: llvm-as -function-summary %s -o %t.bc
+
+; Ensure complete comdat group is materialized
+; RUN: llvm-link %t.bc -S | FileCheck %s
+; CHECK: $linkoncecomdat = comdat any
+; CHECK: @linkoncecomdat = linkonce global i32 2
+; CHECK: @linkoncecomdat_unref_var = linkonce global i32 2, comdat($linkoncecomdat)
+; CHECK: define linkonce void @linkoncecomdat_unref_func() comdat($linkoncecomdat)
+
+$linkoncecomdat = comdat any
+@linkoncecomdat = linkonce global i32 2, comdat($linkoncecomdat)
+@linkoncecomdat_unref_var = linkonce global i32 2, comdat($linkoncecomdat)
+define linkonce void @linkoncecomdat_unref_func() comdat($linkoncecomdat) {
+  ret void
+}
+; Reference one member of comdat so that comdat is generated.
+define void @ref_linkoncecomdat() {
+  load i32, i32* @linkoncecomdat, align 4
+  ret void
+}
diff --git a/llvm/test/Linker/only-needed-named-metadata.ll b/llvm/test/Linker/only-needed-named-metadata.ll
index 36b42590628..a0df5bf2238 100644
--- a/llvm/test/Linker/only-needed-named-metadata.ll
+++ b/llvm/test/Linker/only-needed-named-metadata.ll
@@ -25,17 +25,6 @@
 ; ONLYNEEDED-NOT:@globalfunc1()
 ; ONLYNEEDED-NOT:@analias
 ; ONLYNEEDED-NOT:@globalfunc2()
-; ONLYNEEDED-NOT:@c1_c
-; ONLYNEEDED-NOT:@c1()
-
-$c1 = comdat any
-@c1_c = global i32 0, comdat($c1)
-define void @c1() comdat {
-  ret void
-}
-define void @c1_a() comdat($c1) {
-  ret void
-}
 
 @X = global i32 5
 @U = global i32 6
@@ -64,7 +53,7 @@ entry:
   ret void
 }
 
-!llvm.named = !{!0, !1, !2, !3, !4, !5, !6, !7}
+!llvm.named = !{!0, !1, !2, !3, !4, !5, !6}
 !0 = !{i32 ()* @unused}
 !1 = !{i32* @U}
 !2 = !{i32 ()* @unused_linkonce}
@@ -72,4 +61,3 @@ entry:
 !4 = !{void (...)* @weakalias}
 !5 = !{void (...)* @analias}
 !6 = !{void (...)* @linkoncealias}
-!7 = !{void ()* @c1}