Re: [PATCH] alpha: add -mlra and enable LRA by default on BWX targets

On Mon, Jul 20, 2026 at 12:26 PM Matt Turner <[email protected]> wrote:
>
> Alpha is one of the last targets still forcing TARGET_LRA_P to false, and
> reload is slated for removal (PR113932).  Add a transitional -mlra option,
> following the hppa pattern (r16-5534), so that -mno-lra remains available as
> an escape hatch until reload is deleted.
>
> LRA is enabled by default only on BWX targets.  On non-BWX targets a QImode or
> HImode pseudo that has to be spilled reaches the target's reload_in<mode> /
> reload_out<mode> secondary-reload path, which LRA does not yet drive correctly
> (PR117185: LRA either loops generating reload insns or passes a pseudo where
> get_unaligned_address expects a MEM).  BWX has real byte/word memory
> instructions and does not need that path, so it is unaffected.  Gating the
> default on TARGET_BWX enables LRA where it is known good and leaves non-BWX on
> reload until PR117185 is resolved.  -mlra / -mno-lra override the default in
> either direction.
>
> The default is resolved in alpha_option_override once TARGET_BWX is final, so
> it tracks -mcpu (e.g. -mcpu=ev4 selects reload, -mcpu=ev56 selects LRA) rather
> than only the configured default CPU.
>
> Tested with an alpha-linux-gnu cross (both ev4/non-BWX and --with-cpu=ev56/BWX,
> --enable-checking=yes,rtl): libgcc, libgomp and libstdc++ build cleanly under
> LRA, and gcc.c-torture/execute under qemu-alpha at -O0 and -O2 gives identical
> results with -mlra and -mno-lra on both configurations (3380 results each, no
> differences).  A native ev56 bootstrap with c,c++,m2 completes and, comparing a
> full make check-gcc/check-g++ at the default (LRA) against --target_board
> unix/-mno-lra (reload), LRA shows no correctness regressions: gcc unexpected
> failures drop from 626 to 541 and g++ from 57 to 56, with the only LRA-only
> differences being debug-info-quality (gcc.dg/guality) shifts in LRA's favor.
> The prerequisite middle-end fix for the BWX m2 miscompile is PR117184.
>
> gcc/
>         * config/alpha/alpha.opt (mlra): New option.
>         * config/alpha/alpha.cc (alpha_option_override): Default alpha_lra_p
>         to TARGET_BWX when not set explicitly.
>         (alpha_use_lra_p): New function.
>         (TARGET_LRA_P): Define to it instead of hook_bool_void_false.
> ---

Hi Vlad and Peter,

I could really use your review on this patch as well as your feedback
on the questions in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117185#c8

Thank you,
Matt