[cfe-dev] Line numbers in debug info for range based for

[David Blaikie]

On Fri, May 2, 2014 at 2:16 PM, Justin Bogner <mail at justinbogner.com> wrote:
> When we emit a range-based for, we get debug info for the __range,
> __begin, and __end variables of the equivalent construct:
>
>   {
>     auto && __range = range-init;
>     for (auto __begin = begin-expr, __end = end-expr;
>          __begin != __end; ++__begin) {
>       for-range-declaration = *__begin;
>       // ...
>     }
>   }
>
> Currently, these variables don't have any line information associated
> with them. It looks to me like they did before r188651:
>
>   commit fc946271e008544b518321fdecc77ca076663c12
>   Author: David Blaikie <dblaikie at gmail.com>
>   Date:   Mon Aug 19 03:37:48 2013 +0000
>
>       DebugInfo: Do not include line/file info for artificial parameters &
>       parameters of artificial functions
>
>       git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188651
>       91177308-0d34-0410-b5e6-96231b3b80d8
>
> That commit message is specifically about functions, so it's not clear
> if the change to artificial variables was intentional.
>
> Should these variables have line information? On the one hand, they're
> artificial, but on the other, they do have a pretty obvious source
> location they correspond to.
>
> Thoughts?

Off-hand thought: do you have a debug info consumer that would benefit
from this information? (if so, I'd be curious to hear what the
consumer is/how it's using this information)

And the usual retort: GCC does the same thing:

0x0000008c:         DW_TAG_variable [5]
                      DW_AT_name [DW_FORM_strp] (
.debug_str[0x00000019] = "__for_range")
                      DW_AT_type [DW_FORM_ref4] (cu + 0x00d1 => {0x000000d1})
                      DW_AT_artificial [DW_FORM_flag_present]   (true)
                      DW_AT_location [DW_FORM_exprloc]  (<0x2> 91 58 )

0x00000098:         DW_TAG_variable [5]
                      DW_AT_name [DW_FORM_strp] (
.debug_str[0x00000025] = "__for_begin")
                      DW_AT_type [DW_FORM_ref4] (cu + 0x00d7 => {0x000000d7})
                      DW_AT_artificial [DW_FORM_flag_present]   (true)
                      DW_AT_location [DW_FORM_exprloc]  (<0x2> 91 60 )

0x000000a4:         DW_TAG_variable [5]
                      DW_AT_name [DW_FORM_strp] (
.debug_str[0x00000031] = "__for_end")
                      DW_AT_type [DW_FORM_ref4] (cu + 0x00d7 => {0x000000d7})
                      DW_AT_artificial [DW_FORM_flag_present]   (true)
                      DW_AT_location [DW_FORM_exprloc]  (<0x2> 91 50 )