[llvm-dev] ThinLTO Bug ?
Teresa Johnson via llvm-dev
llvm-dev at lists.llvm.org
Mon Jul 30 09:18:44 PDT 2018
I took a quick look and it looks like the declare of @b is fine, but the
call in @a is using a different type (the "type opaque"). I dumped the
module at the point of the failure, shown below. This was with the change
of !9 in a.ll to be a class type.
Xin - can you file a bug and cc me on it and also reply here with the bug
number? I am traveling all this week and next and likely won't have a
chance to look more until afterwards. Hopefully someone else can take a
look in the meantime.
Teresa
; ModuleID = 'ld-temp.o'
source_filename = "ld-temp.o"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
%0 = type opaque
%struct.TA = type {}
@gv = external dso_local global %struct.TA*
define i32 @c() !dbg !13 {
%1 = bitcast %struct.TA** @gv to i8*
unreachable
}
declare i1 @b(%struct.TA*)
define i1 @a(%struct.TA*) {
%2 = call i1 bitcast (i1 (%struct.TA*)* @b to i1 (%0*)*)(%struct.TA* %0)
unreachable
}
!llvm.dbg.cu = !{!0, !6}
!llvm.module.flags = !{!11, !12}
!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1,
isOptimized: false, runtimeVersion: 0, emissionKind: NoDebug,
retainedTypes: !2)
!1 = !DIFile(filename: "f2", directory: "")
!2 = !{!3}
!3 = distinct !DICompositeType(tag: DW_TAG_class_type, scope: !5, file: !4,
identifier: "SHARED")
!4 = !DIFile(filename: "f1", directory: "")
!5 = distinct !DISubprogram(scope: null, isLocal: false, isDefinition:
true, isOptimized: false, unit: !6)
!6 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !4,
isOptimized: false, runtimeVersion: 0, emissionKind: NoDebug,
retainedTypes: !7)
!7 = !{!8, !3}
!8 = !DICompositeType(tag: DW_TAG_class_type, scope: !5, file: !4,
templateParams: !9)
!9 = !{!10}
!10 = !DITemplateValueParameter(value: i1 (%0*)* bitcast (i1 (%struct.TA*)*
@b to i1 (%0*)*))
!11 = !{i32 2, !"Debug Info Version", i32 3}
!12 = !{i32 1, !"ThinLTO", i32 0}
!13 = distinct !DISubprogram(scope: null, isLocal: false, isDefinition:
true, isOptimized: false, unit: !0)
On Mon, Jul 30, 2018 at 7:06 AM Xin Tong via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On Mon, Jul 30, 2018 at 6:52 AM <paul.robinson at sony.com> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of
> Xin
> > > Tong via llvm-dev
> > > Sent: Friday, July 27, 2018 9:33 PM
> > > To: llvm-dev
> > > Subject: [llvm-dev] ThinLTO Bug ?
> > >
> > > Hi
> > >
> > > I have encountered a module verification failure when running 2 files
> > > with thin-lto (I hit this bug in the link step in LTO on a really
> > > large program and I reduced to this test case).
> > >
> > >
> > > ~/llvmfb/build-debug/bin/llvm-lto2 run -o c a.o b.o -r a.o,c,px -r
> > > b.o,a,px -r b.o,b,px -r a.o,gv -r b.o,gv
> > > Called function is not the same type as the call!
> > > %2 = call i1 bitcast (i1 (%struct.TA*)* @b to i1 (%0*)*)(%struct.TA*
> %0)
> > > in function a
> > > LLVM ERROR: Broken function found, compilation aborted!
> > >
> > >
> > > My understanding why this is happening is roughly as follow. I would
> > > like to check with people whether this is a real bug. And also would
> > > like to help fixing it with other people’s help if it’s a real bug. I
> > > am quite new to this part of LLVM.
> > >
> > > 1. DICompositeType “SHARED” in a.ll is ODRed with the one in b.ll at
> load
> > > time.
> >
> > I know relatively little about LTO but I see that in a.ll, "SHARED" is
> > described as a DW_TAG_class_type while in b.ll it is DW_TAG_array_type.
> > This suggests that you have an ODR violation in your source code.
> >
> Hi Paul
>
> Thanks for pointing it out.
> I fixed this by making in b.ll and the same failure persists.
> !9 = !DICompositeType(tag: DW_TAG_class_type, file: !3, identifier:
> "SHARED", scope: !8)
>
> -Xin
>
>
> > ODR violations in LTO tend to exhibit as a "broken module" or "broken
> > function" at link time. It would be nice to diagnose these better,
> > admittedly.
> > --paulr
> >
> > > 2. %struct.TA.0 (renamed from %struct.TA at load time) = type opaque
> > > and i1 (%struct.TA.0*)* @b in b.ll gets pulled into the destination
> > > module when we are merging in a.ll.
> > > 3. We only found out that %struct.TA.0 maps to %struct.TA when we link
> > > in b.ll because of the @gv global variable.
> > > 4. Then we have a problem, because declare i1 @b(%struct.TA.0*) in
> > > a.ll should have been remapped due to what we found in #3, but was
> > > not. This eventually leads to the IR verifier failure.
> > >
> > > Thanks
> > > -Xin
> > >
> > >
> > > Commands to reproduce with ToT LLVM:
> > > ===============================
> > >
> > > ~/llvm/build-debug/bin/opt -module-summary -o a.o a.ll
> > > ~/llvm/build-debug/bin/opt -module-summary -o b.o b.ll
> > > ~/llvm/build-debug/bin/llvm-lto2 run -o c a.o b.o -r a.o,c,px -r
> > > b.o,a,px -r b.o,b,px -r a.o,gv -r b.o,gv
> > >
> > >
> > >
> > > [~/thinltobug]$ cat a.ll
> > >
> > > target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
> > >
> > > target triple = "x86_64-unknown-linux-gnu"
> > >
> > > %struct.TA = type {}
> > >
> > >
> > >
> > > @gv = dso_local global %struct.TA * zeroinitializer
> > >
> > > define i32 @c() !dbg !6 {
> > >
> > > bitcast %struct.TA ** @gv to i8*
> > >
> > > unreachable
> > >
> > > }
> > >
> > >
> > >
> > >
> > >
> > > !llvm.module.flags = !{!0, !1}
> > >
> > > !llvm.dbg.cu = !{!2}
> > >
> > > !0 = !{i32 2, !"Debug Info Version", i32 3}
> > >
> > > !1 = !{i32 1, !"ThinLTO", i32 0}
> > >
> > > !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3,
> > > retainedTypes: !4)
> > >
> > > !3 = !DIFile(filename: "f2", directory: "")
> > >
> > > !4 = !{!5}
> > >
> > > !5 = !DICompositeType(tag: DW_TAG_class_type, file: !3, flags:
> > > DIFlagFwdDecl, identifier: "SHARED")
> > >
> > > !6 = distinct !DISubprogram(unit: !2)
> > >
> > >
> > >
> > > [~/thinltobug]$ cat b.ll
> > >
> > > target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
> > >
> > > target triple = "x86_64-unknown-linux-gnu"
> > >
> > >
> > >
> > > %struct.TA = type opaque
> > >
> > >
> > >
> > > @gv = external dso_local global %struct.TA *
> > >
> > >
> > >
> > > define i1 @b(%struct.TA*) {
> > >
> > > unreachable
> > >
> > > }
> > >
> > >
> > >
> > > define i1 @a(%struct.TA* %a) {
> > >
> > > call i1 @b(%struct.TA* %a)
> > >
> > > unreachable
> > >
> > > }
> > >
> > >
> > >
> > > !llvm.module.flags = !{!0, !1}
> > >
> > > !llvm.dbg.cu = !{!2}
> > >
> > > !0 = !{i32 2, !"Debug Info Version", i32 3}
> > >
> > > !1 = !{i32 1, !"ThinLTO", i32 0}
> > >
> > > !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3,
> > > retainedTypes: !4)
> > >
> > > !3 = !DIFile(filename: "f1", directory: "")
> > >
> > > !4 = !{!5, !9}
> > >
> > > !5 = !DICompositeType(tag: DW_TAG_class_type, file: !3,
> > > templateParams: !6, scope: !8)
> > >
> > > !6 = !{!7}
> > >
> > >
> > >
> > > ; The reference to @b and struct.TA.0 (renamed) that will be loaded in
> > > %a.o
> > >
> > >
> > >
> > > !7 = !DITemplateValueParameter(value: i1 (%struct.TA*)* @b)
> > >
> > > !8 = distinct !DISubprogram(unit: !2)
> > >
> > >
> > >
> > > !9 = !DICompositeType(tag: DW_TAG_array_type, identifier: "SHARED",
> scope:
> > > !8)
> > > _______________________________________________
> > > LLVM Developers mailing list
> > > llvm-dev at lists.llvm.org
> > > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> _______________________________________________
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--
Teresa Johnson | Software Engineer | tejohnson at google.com | 408-460-2413
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