[llvm-dev] Extracting the !dbg property from LLVM IR function calls

[David Blaikie via llvm-dev]

The !69 and !29 refer to metadata (look further down in the LLVM IR dump)
that looks something like this:

!10 = !DILocation(line: 3, column: 3, scope: !7)

Which is where the 'line' value is stored (so the line is not 69 or 29).

When you extract the function, only the referenced metadata is brought with
it, so it gets renumbered - but the semantics remain the same - the
line/column/scope is preserved. It's just there's fewer metadata nodes, so
the metadata node number is smaller.

On Wed, Jul 8, 2020 at 11:23 AM Shishir V Jessu via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hello,
>
> I am compiling a program with debugging information, and am attempting to
> extract !dbg numbers from function calls in LLVM IR. However, I've found a
> few inconsistencies. For example, this call exists in my module:
>
> %1 = tail call i1 @llvm.type.test(i8* bitcast (i32 (i32)* @_Z5otheri to
> i8*), metadata !"_ZTSFiiE") #5, *!dbg !69*, !nosanitize !2
>
> I would like to extract the 69 from this line in my LLVM pass, but when I
> dump() the corresponding CallInst, I see the following:
>
> %1 = tail call i1 @llvm.type.test(i8* bitcast (i32 (i32)* @_Z5otheri to
> i8*), metadata !"_ZTSFiiE") #5, *!dbg !29*, !nosanitize !2
>
> And finally, the line *CallInst -> getDebugLoc() -> getLine()* returns
> *61* for this call, not 69 or 29.
>
> Am I misunderstanding the purpose of getDebugLoc() for a CallInst? Is
> there any way I can extract the correct !dbg for a given line? Thanks for
> your help!
>
> Best,
> Shishir Jessu
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