[LLVMdev] Missing metadata for volatile variables

[Duncan Sands]

Hi Cindy,

> I am using the dragonegg plugin to produce bitcode for the following
> small C program:
>
> int main() {
> 1:  int x = -5;
> 2:  x = 6;
> 3:  return 0;
> }
>
> The assignments on lines 1 and 2 are removed even when no optimization
> flags are specified.

as the value of x is never used the compiler doesn't bother outputting it
as you noticed.

  I tried making variable "x" volatile, which
> prevents the assignments from being removed, however I am no longer
> able to recover the original name of the variable "x". Below is the
> bitcode generated. It seems like the metadata does not mention "x"
> anywhere. Am I missing something?

Unfortunately dragonegg doesn't currently output *any* debug info for variables.
This would probably be easy enough to fix but no one got around to it yet.
Please feel free to open a bug report.

Ciao, Duncan.

>
> Thank you,
> Cindy
>
>
> =========
>
> ; ModuleID = 'post/tests/test1/source.c'
> target datalayout =
> "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-f128:128:128-n8:16:32"
> target triple = "i386-pc-linux-gnu"
>
> module asm "\09.ident\09\22GCC: (GNU) 4.5.2 LLVM: exported\22"
>
> %int = type i32
>
> define i32 @main() nounwind {
> entry:
>    %memtmp = alloca i32
>    %memtmp1 = alloca i32
>    %"alloca point" = bitcast i32 0 to i32
>    %"ssa point" = bitcast i32 0 to i32
>    br label %"2", !dbg !6
>
> "2":                                              ; preds = %entry
>    call void @llvm.dbg.declare(metadata !{i32* %memtmp}, metadata !7), !dbg !9
>    volatile store i32 -5, i32* %memtmp, align 4, !dbg !9
>    volatile store i32 6, i32* %memtmp, align 4, !dbg !10
>    store i32 0, i32* %memtmp1, align 1, !dbg !11
>    br label %return, !dbg !11
>
> return:                                           ; preds = %"2"
>    %retval = load i32* %memtmp1, !dbg !11
>    ret i32 %retval, !dbg !11
> }
>
> declare void @llvm.dbg.declare(metadata, metadata) nounwind readnone
>
> !llvm.dbg.sp = !{!0}
>
> !0 = metadata !{i32 589870, i32 0, metadata !1, metadata !"main",
> metadata !"main", metadata !"main", metadata !1, i32 1, metadata !3,
> i1 false, i1 true, i32 0, i32 0, null, i32 0, i1 false, null} ; [
> DW_TAG_subprogram ]
> !1 = metadata !{i32 589865, metadata !"source.c", metadata
> !"/afs/cs.wisc.edu/u/c/r/crubio/trunk/post/tests/test1", metadata !2}
> ; [ DW_TAG_file_type ]
> !2 = metadata !{i32 589841, i32 0, i32 1, metadata !"source.c",
> metadata !"post/tests/test1", metadata !"4.5.2", i1 true, i1 false,
> metadata !"", i32 0} ; [ DW_TAG_compile_unit ]
> !3 = metadata !{i32 589845, 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 589860, 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 1, i32 0, metadata !0, null}
> !7 = metadata !{i32 590080, metadata !0, metadata !"memtmp", metadata
> !1, i32 2, metadata !8, i32 0} ; [ DW_TAG_auto_variable ]
> !8 = metadata !{i32 589877, metadata !1, metadata !"", metadata !1,
> i32 0, i64 32, i64 32, i64 0, i32 0, metadata !5} ; [
> DW_TAG_volatile_type ]
> !9 = metadata !{i32 2, i32 0, metadata !0, null}
> !10 = metadata !{i32 3, i32 0, metadata !0, null}
> !11 = metadata !{i32 4, i32 0, metadata !0, null}
>
> ========
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