Hi,
It seems that current linker "drops" updated llvm::Value * references
in metadata. Here goes an example. We have a two-line source file
a.c:
static int x;
void foo() { x = 1; }
and a similar b.c:
static int x;
void bar() { x = 1; }
They both have an internal variable x; one of them will be renamed (to
x1) during linking.
clang -emit-llvm -c -g a.c
clang -emit-llvm -c -g b.c
llvm-link -o t.bc a.o b.o
Before linking we can see the following lines in both bitcode files
from a.c and b.c, where the last element of !5 refers to the internal
variable x.
!llvm.dbg.sp = !{!1}
!5 = metadata !{i32 655412, i32 0, metadata !0, metadata !"x",
metadata !"x", metadata !"", metadata !2, i32 1, metadata
!6, i32 1,
i32 1, i32* @x} ; [ DW_TAG_variable ]
However after linking the last element of !11 becomes null. I was
expecting that it would refer to the renamed x1.
!llvm.dbg.gv = !{!9, !11}
!9 = metadata !{i32 655412, i32 0, metadata !0, metadata !"x",
metadata !"x", metadata !"", metadata !3, i32 1, metadata
!10, i32 1,
i32 1, i32* @x} ; [ DW_TAG_variable ]
!11 = metadata !{i32 655412, i32 0, metadata !1, metadata !"x",
metadata !"x", metadata !"", metadata !7, i32 1, metadata
!12, i32 1,
i32 1, null} ; [ DW_TAG_variable ]
Is it intentional or a bug? Thanks.
- xi
On Aug 4, 2011, at 8:21 AM, Xi Wang wrote:> Hi, > > It seems that current linker "drops" updated llvm::Value * references > in metadata. Here goes an example. We have a two-line source file > a.c: > > static int x; > void foo() { x = 1; } > > and a similar b.c: > > static int x; > void bar() { x = 1; } > > They both have an internal variable x; one of them will be renamed (to > x1) during linking. > > clang -emit-llvm -c -g a.c > clang -emit-llvm -c -g b.c > llvm-link -o t.bc a.o b.o > > Before linking we can see the following lines in both bitcode files > from a.c and b.c, where the last element of !5 refers to the internal > variable x. > > !llvm.dbg.sp = !{!1} > !5 = metadata !{i32 655412, i32 0, metadata !0, metadata !"x", > metadata !"x", metadata !"", metadata !2, i32 1, metadata !6, i32 1, > i32 1, i32* @x} ; [ DW_TAG_variable ] > > However after linking the last element of !11 becomes null. I was > expecting that it would refer to the renamed x1. > > !llvm.dbg.gv = !{!9, !11} > !9 = metadata !{i32 655412, i32 0, metadata !0, metadata !"x", > metadata !"x", metadata !"", metadata !3, i32 1, metadata !10, i32 1, > i32 1, i32* @x} ; [ DW_TAG_variable ] > !11 = metadata !{i32 655412, i32 0, metadata !1, metadata !"x", > metadata !"x", metadata !"", metadata !7, i32 1, metadata !12, i32 1, > i32 1, null} ; [ DW_TAG_variable ] > > Is it intentional or a bug? Thanks.It's a bug, probably a regression. Please file a bugzilla report. Thanks, - Devang
I looked at an earlier version. NamedMDNodes were linked after global values. Current trunk version links NamedMDNodes before that, though the comment says otherwise: "We do this after linking GlobalValues so that MDNodes that reference GlobalValues are properly remapped". see ModuleLinker::run in lib/Linker/LinkModules.cpp. If I move the call to linkNamedMDNodes in ModuleLinker::run to the last step (just before return false), everything looks good. Not sure if linkNamedMDNodes must be called earlier. - xi On Thu, Aug 4, 2011 at 1:22 PM, Devang Patel <dpatel at apple.com> wrote:> > On Aug 4, 2011, at 8:21 AM, Xi Wang wrote: > >> Hi, >> >> It seems that current linker "drops" updated llvm::Value * references >> in metadata. Here goes an example. We have a two-line source file >> a.c: >> >> static int x; >> void foo() { x = 1; } >> >> and a similar b.c: >> >> static int x; >> void bar() { x = 1; } >> >> They both have an internal variable x; one of them will be renamed (to >> x1) during linking. >> >> clang -emit-llvm -c -g a.c >> clang -emit-llvm -c -g b.c >> llvm-link -o t.bc a.o b.o >> >> Before linking we can see the following lines in both bitcode files >> from a.c and b.c, where the last element of !5 refers to the internal >> variable x. >> >> !llvm.dbg.sp = !{!1} >> !5 = metadata !{i32 655412, i32 0, metadata !0, metadata !"x", >> metadata !"x", metadata !"", metadata !2, i32 1, metadata !6, i32 1, >> i32 1, i32* @x} ; [ DW_TAG_variable ] >> >> However after linking the last element of !11 becomes null. I was >> expecting that it would refer to the renamed x1. >> >> !llvm.dbg.gv = !{!9, !11} >> !9 = metadata !{i32 655412, i32 0, metadata !0, metadata !"x", >> metadata !"x", metadata !"", metadata !3, i32 1, metadata !10, i32 1, >> i32 1, i32* @x} ; [ DW_TAG_variable ] >> !11 = metadata !{i32 655412, i32 0, metadata !1, metadata !"x", >> metadata !"x", metadata !"", metadata !7, i32 1, metadata !12, i32 1, >> i32 1, null} ; [ DW_TAG_variable ] >> >> Is it intentional or a bug? Thanks. > > It's a bug, probably a regression. Please file a bugzilla report. > Thanks, > - > Devang >