[x86 PATCH] Don't use insvti_{high,low}part with -O0 (for compile-time).

[x86 PATCH] Don't use insvti_{high,low}part with -O0 (for compile-time).

[Roger Sayle]

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This patch attempts to help with PR rtl-optimization/110587, a regression
of -O0 compile time for the pathological pr28071.c.  My recent patch helps
a bit, but hasn't returned -O0 compile-time to where it was before my
ix86_expand_move changes.  The obvious solution/workaround is to guard
these new TImode parameter passing optimizations with "&& optimize", so
they don't trigger when compiling with -O0.  The very minor complication
is that "&& optimize" alone leads to the regression of pr110533.c, where
our improved TImode parameter passing fixes a wrong-code issue with naked
functions, importantly, when compiling with -O0.  This should explain
the one line fix below "&& (optimize || ix86_function_naked (cfun))".

I've an additional fix/tweak or two for this compile-time issue, but
this change eliminates the part of the regression that I've caused.

This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32}
with no new failures.  Ok for mainline?

2023-07-22  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        * config/i386/i386-expand.cc (ix86_expand_move): Disable the
        64-bit insertions into TImode optimizations with -O0, unless
        the function has the "naked" attribute (for PR target/110533).

Cheers,
Roger
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diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc
index 7e94447..cdef95e 100644
--- a/gcc/config/i386/i386-expand.cc
+++ b/gcc/config/i386/i386-expand.cc
@@ -544,6 +544,7 @@ ix86_expand_move (machine_mode mode, rtx operands[])
 
   /* Special case inserting 64-bit values into a TImode register.  */
   if (TARGET_64BIT
+      && (optimize || ix86_function_naked (current_function_decl))
       && (mode == DImode || mode == DFmode)
       && SUBREG_P (op0)
       && GET_MODE (SUBREG_REG (op0)) == TImode

Re: [x86 PATCH] Don't use insvti_{high,low}part with -O0 (for compile-time).

[Uros Bizjak]

On Sat, Jul 22, 2023 at 4:17 PM Roger Sayle <roger@nextmovesoftware.com> wrote:
>
>
> This patch attempts to help with PR rtl-optimization/110587, a regression
> of -O0 compile time for the pathological pr28071.c.  My recent patch helps
> a bit, but hasn't returned -O0 compile-time to where it was before my
> ix86_expand_move changes.  The obvious solution/workaround is to guard
> these new TImode parameter passing optimizations with "&& optimize", so
> they don't trigger when compiling with -O0.  The very minor complication
> is that "&& optimize" alone leads to the regression of pr110533.c, where
> our improved TImode parameter passing fixes a wrong-code issue with naked
> functions, importantly, when compiling with -O0.  This should explain
> the one line fix below "&& (optimize || ix86_function_naked (cfun))".
>
> I've an additional fix/tweak or two for this compile-time issue, but
> this change eliminates the part of the regression that I've caused.
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-m32}
> with no new failures.  Ok for mainline?
>
> 2023-07-22  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
>         * config/i386/i386-expand.cc (ix86_expand_move): Disable the
>         64-bit insertions into TImode optimizations with -O0, unless
>         the function has the "naked" attribute (for PR target/110533).

LGTM, but please add some comments, why only when optimizing (please
mention PR110587) and especially mention PR110533 on why the naked
attribute is allowed.

Thanks,
Uros.

> Cheers,
> Roger
> --
>