On Tue, 2023-04-18 at 20:39 +0800, WANG Xuerui wrote:
> Hi,
>
> Thanks for helping confirming on GCC and porting this! I'd never know
> even GCC lacked this adaptation without someone actually checking... Too
> many things are taken for granted these days.
>
> On 2023/4/18 20:17, Xi Ruoyao wrote:
> > According to Xuerui's LLVM changeset [1], doing so can make a
> > significant performace gain.
> >
> > Bootstrapped and regtested on loongarch64-linux-gnu. Ok for GCC 14?
> >
> > [1]:https://reviews.llvm.org/D148622
> >
> > gcc/ChangeLog:
> >
> > * config/loongarch/loongarch.cc
> > (loongarch_option_override_internal): If -falign-functions is
> > used but the alignment is not explicitly specified, set it to
> > 4 * loongarch_issue_rate (). Likewise for -falign-loops.
> > ---
> > gcc/config/loongarch/loongarch.cc | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> >
> > diff --git a/gcc/config/loongarch/loongarch.cc
> > b/gcc/config/loongarch/loongarch.cc
> > index 06fc1cd0604..6552484de7c 100644
> > --- a/gcc/config/loongarch/loongarch.cc
> > +++ b/gcc/config/loongarch/loongarch.cc
> > @@ -6236,6 +6236,17 @@ loongarch_option_override_internal (struct
> > gcc_options *opts)
> > && !opts->x_optimize_size)
> > opts->x_flag_prefetch_loop_arrays = 1;
> >
> > + /* Align functions and loops to (issue rate) * (insn size) to improve
> > + the throughput of the fetching units. */
> What about gating all of these on !opts->x_optimize_size, similar to
> what aarch64 does?
opts->x_flag_align_functions and opts->x_flag_align_loops are only set
with -O2 or above unless the user manually uses -falign-functions or -
falign-loops. If the user uses "-Os -falign-functions" as CFLAGS I'd
assume s(he) wants to optimize for size but keep the optimized function
alignment.
> > + char *align = XNEWVEC (char, 16);
> > + sprintf (align, "%d", loongarch_issue_rate () * 4);
> > +
> > + if (opts->x_flag_align_functions && !opts->x_str_align_functions)
> > + opts->x_str_align_functions = align;
> > +
> > + if (opts->x_flag_align_loops && !opts->x_str_align_loops)
> > + opts->x_str_align_loops = align;
> > +
> > if (TARGET_DIRECT_EXTERN_ACCESS && flag_shlib)
> > error ("%qs cannot be used for compiling a shared library",
> > "-mdirect-extern-access");
> Otherwise LGTM, thanks!
--
Xi Ruoyao <xry...@xry111.site>
School of Aerospace Science and Technology, Xidian University
