[Bug target/91767] [10 regression] After r274953, clang-compiled xgcc segfaults during RTL pass: stv

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91767

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Dimitry Andric from comment #5)
> Hmm, it appears that this diff "fixes" it:
> 
> diff --git a/gcc/config/i386/i386-features.c
> b/gcc/config/i386/i386-features.c
> index 9505b4a1330..091a59f3cb9 100644
> --- a/gcc/config/i386/i386-features.c
> +++ b/gcc/config/i386/i386-features.c
> @@ -1166,7 +1166,11 @@ general_scalar_chain::convert_registers ()
>    bitmap_iterator bi;
>    unsigned id;
>    EXECUTE_IF_SET_IN_BITMAP (defs_conv, 0, id, bi)
> -    defs_map.put (regno_reg_rtx[id], gen_reg_rtx (smode));
> +    {
> +      rtx key = regno_reg_rtx[id];
> +      rtx val = gen_reg_rtx (smode);
> +      defs_map.put (key, val);
> +    }
>    EXECUTE_IF_SET_IN_BITMAP (insns_conv, 0, id, bi)
>      for (df_ref ref = DF_INSN_UID_DEFS (id); ref; ref = DF_REF_NEXT_LOC
> (ref))
>        if (bitmap_bit_p (defs_conv, DF_REF_REGNO (ref)))
> 
> but obviously that can't be right, unless gen_reg_rtx() is doing something
> horrible to regno_reg_rtx[].  I only see it adding another element at the
> end, though.
> 
> I think this might indeed be some clang code generation bug, as the assembly
> looks a little different with the above patch applied.
> 
> Digging further...

Ok, just a quick note, it can make a different if defs_map.put takes a constant
reference for its arguments.  As gen_reg_rtx can free the old regno_reg_rtx.

Basically the old code is equivalant to:

 +    {
 +      const rtx &key = regno_reg_rtx[id];
 +      const rtx &val = gen_reg_rtx (smode);
 +      defs_map.put (key, val);
 +    }

so taking the reference of a pointer which can be free is a big no-no.