Re: Help with bisecting a test suite regression in GCC

[Jonathan Wakely <jwakely.gcc@gmail.com>]

On Sat, 26 Mar 2022 at 22:42, John Scott via Gcc-help
<gcc-help@gcc.gnu.org> wrote:
>
> Hi,
>
> While working on upgrading the gcc-sh-elf Debian package from gcc 11 to
> gcc 12, I think I've found a regression. I'm able to reproduce it with
> an upstream bare-metal build.
>
> I've had a hard time figuring out how to bisect it. A naive run with
> git bisect start
> git bisect new .

"." is not a tag or commit revision. I don't know what this does.

> git bisect old releases/gcc-11.2.0

This tag is on the gcc-11 branch, which is not in the history of gcc-12.

I think what you want is:
git bisect start
git bisect new master
git bisect old `git merge-base releases/gcc-11.2.0 master`

This will bisect between the point where the gcc-11 branch was created
and the current head of master.


>
> fails with
> The merge base 250f234988b6231669a720c52101d3686d645072 is new.
> The property has changed between 250f234988b6231669a720c52101d3686d645072 and [7ca388565af176bd4efd4f8db1e5e9e11e98ef45].
> error: bisect run failed: 'git bisect--helper --bisect-state (null)' exited with error code -3
>
> I'm not enough of a Git or GCC wizard to get further. Does anyone have
> any advice so I can make an informative bug report?