[llvm-commits] JIT: Emitting a debug location after an instruction

[nicolas geoffray]

You are right. My changes would not work (the test I had was too simple).

So I should probably hook that up with the GC. Sounds fun!

Thanks Jeffrey for the explanations.

Nicolas

On Tue, Aug 24, 2010 at 4:08 AM, Jeffrey Yasskin <jyasskin at google.com>wrote:

> On Mon, Aug 23, 2010 at 9:37 PM, nicolas geoffray
> <nicolas.geoffray at gmail.com> wrote:
> >
> >
> > On Mon, Aug 23, 2010 at 8:57 PM, Jeffrey Yasskin <jyasskin at google.com>
> > wrote:
> >>
> >> I'm not sure processDebugLoc does what you need it to, even with your
> >> changes. It only records an address when the DebugLoc changes, and
> >> that's not guaranteed to happen exactly on the call
> >> MachineInstruction. (Unless you've done something to ensure it does?)
> >
> > Each call instruction and only call instructions have metadata associated
> to
> > it. So I am sure emitting the debug location after emitting the call
> > instructions work for my case.
>
> A CallInst in the IR expands to several MachineInstructions, all of
> which have the same DebugLoc (and which may be rearranged/interleaved
> with other DebugLoc'ed MIs by the SelectionDAG (ScheduleDAG?)). For
> example, the following IR:
>
> @.str = private constant [12 x i8] c"Hello World\00" ; <[12 x i8]*>
> [#uses=1]
>
> define i32 @main() nounwind {
> entry:
>  %call = tail call i32 @puts(i8* getelementptr inbounds ([12 x i8]*
> @.str, i32 0, i32 0)) nounwind, !dbg !6 ; <i32> [#uses=0]
>  ret i32 0, !dbg !8
> }
>
> declare i32 @puts(i8* nocapture) nounwind
>
> !llvm.dbg.sp = !{!0}
>
> !0 = metadata !{i32 524334, i32 0, metadata !1, metadata !"main",
> metadata !"main", metadata !"main", metadata !1, i32 2, metadata !3,
> i1 false, i1 true, i32 0, i32 0, null, i1 false, i1 false, null} ; [
> DW_TAG_subprogram ]
> !1 = metadata !{i32 524329, metadata !"test.c", metadata
> !"/Users/jyasskin/tmp", metadata !2} ; [ DW_TAG_file_type ]
> !2 = metadata !{i32 524305, i32 0, i32 12, metadata !"test.c",
> metadata !"/Users/jyasskin/tmp", metadata !"clang 2.8", i1 true, i1
> true, metadata !"", i32 0} ; [ DW_TAG_compile_unit ]
> !3 = metadata !{i32 524309, metadata !1, metadata !"", metadata !1,
> i32 0, i64 0, i64 0, i64 0, i32 0, null, metadata !4, i32 0, null} ; [
> DW_TAG_subroutine_type ]
> !4 = metadata !{metadata !5}
> !5 = metadata !{i32 524324, metadata !1, metadata !"int", metadata !1,
> i32 0, i64 32, i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ]
> !6 = metadata !{i32 3, i32 3, metadata !7, null}
> !7 = metadata !{i32 524299, metadata !0, i32 2, i32 12} ; [
> DW_TAG_lexical_block ]
> !8 = metadata !{i32 4, i32 1, metadata !7, null}
>
>
> Produces the following MachineFunction:
>
> BB#0: derived from LLVM BB %entry
>        %ESP<def> = SUB32ri8 %ESP, 12, %EFLAGS<imp-def,dead>; dbg:test.c:3:3
>        MOV32mi %ESP, 1, %reg0, 0, %reg0, <ga:@.str>; mem:ST4[Stack]
> dbg:test.c:3:3
>        CALLpcrel32 <ga:@puts>, %EAX<imp-def,dead>, %ESP<imp-use>, ...;
> dbg:test.c:3:3
>        %EAX<def> = MOV32r0 %EFLAGS<imp-def,dead>
>        %ESP<def> = ADD32ri8 %ESP, 12, %EFLAGS<imp-def,dead>; dbg:test.c:4:1
>        RET %EAX<imp-use,kill>; dbg:test.c:4:1
>
> and saves addresses in processDebugLoc at the following
> MachineInstructions:
>
>  %ESP<def> = SUB32ri8 %ESP, 12, %EFLAGS<imp-def,dead>; dbg:test.c:3:3
>  %ESP<def> = ADD32ri8 %ESP, 12, %EFLAGS<imp-def,dead>; dbg:test.c:4:1
>
> That is, not the call instruction. So, I'm not sure why this is
> working for you...
>
> >> Do you have a unit test that shows this works in all cases?
> >
> > Not sure about the "all cases", but at least it is working as intended
> for
> > me and these hooks (emitting before or after) were already present before
> my
> > changes.
> >
> >>
> >> Mapping return addresses to metadata seems like more of a job for the
> >> GC system, but that's not implemented for the JIT, so I can't very
> >> well say to use it instead. :-/
> >
> > Indeed, doing it in the GC system would also work, but the changes would
> be
> > way less straightforward than this simple change in the JITemitter.
> > Nicolas
> > _______________________________________________
> > llvm-commits mailing list
> > llvm-commits at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> >
> >
>
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