x86: Make stringop_algs::stringop_strategy ctor constexpr [PR100246]

  On Tue, Jul 06, 2021 at 11:17:55AM +0100, Iain Sandoe wrote:
> >> The addition of the CTOR is the fix for the C++ compile fail in the PR, the conditional is
> >> only there because the same header is compiled by C and C++.
> > 
> > Whoops sorry - I was confused.  The patch looks OK to me if you add a comment
> > before the CTOR why it was added (maybe quoting the error that happens)
> 
> Thanks, pushed as below.
> Iain
> 
> -------
> 
> X86: Provide a CTOR for stringop_algs [PR100246].
> 
> Several older compilers fail to build modern GCC because of missing
> or incomplete C++11 support.
> 
> Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
> 
> PR bootstrap/100246 - [11/12 Regression] GCC will not bootstrap with clang 3.4/3.5 [xcode 5/6, Darwin 12/13]
> 
> 	PR bootstrap/100246
> 
> gcc/ChangeLog:
> 
> 	* config/i386/i386.h (struct stringop_algs): Define a CTOR for
> 	this type.

Unfortunately, as mentioned in my
https://gcc.gnu.org/pipermail/gcc-patches/2021-November/583289.html
mail, without the new dyninit pass this causes dynamic initialization of
many variables, 6.5KB _GLOBAL__sub_I_* on x86_64 and 12.5KB on i686.

The following so far only lightly tested patch makes the ctor constexpr
so that already the FE is able to statically initialize all those.

I don't have access to Darwin nor to the broken versions of clang, do you
think you could test bootstrap there with this too?
Especially because 11.x is not going to have the dyninit optimization for
sure, it would be nice to do this on the 11 branch too.

2021-11-04  Jakub Jelinek  <jakub@redhat.com>

	PR bootstrap/100246
	* config/i386/i386.h
	(stringop_algs::stringop_strategy::stringop_strategy): Make the ctor
	constexpr.


	Jakub
  

Hi Jakub,

> On 4 Nov 2021, at 10:05, Jakub Jelinek <jakub@redhat.com> wrote:
> 
> On Tue, Jul 06, 2021 at 11:17:55AM +0100, Iain Sandoe wrote:
>>>> The addition of the CTOR is the fix for the C++ compile fail in the PR, the conditional is
>>>> only there because the same header is compiled by C and C++.
>>> 
>>> Whoops sorry - I was confused.  The patch looks OK to me if you add a comment
>>> before the CTOR why it was added (maybe quoting the error that happens)
>> 
>> Thanks, pushed as below.
>> Iain
>> 
>> -------
>> 
>> X86: Provide a CTOR for stringop_algs [PR100246].
>> 
>> Several older compilers fail to build modern GCC because of missing
>> or incomplete C++11 support.
>> 
>> Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
>> 
>> PR bootstrap/100246 - [11/12 Regression] GCC will not bootstrap with clang 3.4/3.5 [xcode 5/6, Darwin 12/13]
>> 
>> 	PR bootstrap/100246
>> 
>> gcc/ChangeLog:
>> 
>> 	* config/i386/i386.h (struct stringop_algs): Define a CTOR for
>> 	this type.
> 
> Unfortunately, as mentioned in my
> https://gcc.gnu.org/pipermail/gcc-patches/2021-November/583289.html
> mail, without the new dyninit pass this causes dynamic initialization of
> many variables, 6.5KB _GLOBAL__sub_I_* on x86_64 and 12.5KB on i686.
> 
> The following so far only lightly tested patch makes the ctor constexpr
> so that already the FE is able to statically initialize all those.
> 
> I don't have access to Darwin nor to the broken versions of clang, do you
> think you could test bootstrap there with this too?

Bootstrap succeeded with Apple clang-503.0.40 (Xcode 5.1.1) on macOS 10.8
which is the earliest version I expect to work (previous xcode impl. have more
C++11 incompatibilities).   So OK from a Darwin PoV.

The other reported toolchain with the issue was GCC-4.9.2 as discussed on
IRC - this also seems OK.

Iain

> Especially because 11.x is not going to have the dyninit optimization for
> sure, it would be nice to do this on the 11 branch too.
> 
> 2021-11-04  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR bootstrap/100246
> 	* config/i386/i386.h
> 	(stringop_algs::stringop_strategy::stringop_strategy): Make the ctor
> 	constexpr.
> 
> --- gcc/config/i386/i386.h.jj	2021-09-28 23:18:35.282563395 +0200
> +++ gcc/config/i386/i386.h	2021-11-04 10:48:47.165086806 +0100
> @@ -78,8 +78,9 @@ struct stringop_algs
>        this issue.  Since this header is used by code compiled with the C
>        compiler we must guard the addition.  */
> #ifdef __cplusplus
> -    stringop_strategy(int _max = -1, enum stringop_alg _alg = libcall,
> -		      int _noalign = false)
> +    constexpr stringop_strategy(int _max = -1,
> +				enum stringop_alg _alg = libcall,
> +				int _noalign = false)
>       : max (_max), alg (_alg), noalign (_noalign) {}
> #endif
>     const int max;
> 
> 	Jakub
>
  

On Thu, Nov 04, 2021 at 12:39:34PM +0000, Iain Sandoe wrote:
> Bootstrap succeeded with Apple clang-503.0.40 (Xcode 5.1.1) on macOS 10.8
> which is the earliest version I expect to work (previous xcode impl. have more
> C++11 incompatibilities).   So OK from a Darwin PoV.
> 
> The other reported toolchain with the issue was GCC-4.9.2 as discussed on
> IRC - this also seems OK.

Yeah, I've been testing it on a short testcase with just enum stringop_alg,
struct stringop_algs and ix86_size_memcpy on godbolt too:
https://godbolt.org/z/vfcz8xen6
enum stringop_alg {
no_stringop, libcall, rep_prefix_1_byte, rep_prefix_4_byte, rep_prefix_8_byte,
loop_1_byte, loop, unrolled_loop, vector_loop, last_alg
};
struct stringop_algs
{
  const enum stringop_alg unknown_size;
  const struct stringop_strategy {
#ifndef NO_CTOR
#ifdef CONSTEXPR
    constexpr
#endif
    stringop_strategy(int _max = -1, enum stringop_alg _alg = libcall, int _noalign = false)
      : max (_max), alg (_alg), noalign (_noalign) {}
#endif
    const int max;
    const enum stringop_alg alg;
    int noalign;
  } size [4];
};
stringop_algs ix86_size_memcpy[2] = {
  {rep_prefix_1_byte, {{-1, rep_prefix_1_byte, false}}},
  {rep_prefix_1_byte, {{-1, rep_prefix_1_byte, false}}}};
and tested the various cases, no stringop_strategy ctor at all, the ctor
and ctor with constexpr.
clang before 3.3 is unhappy about all the 3 cases, clang 3.3 and 3.4
is ok with ctor and ctor with constexpr and optimizes it into static
initialization, clang 3.5+ is ok with all 3 versions and optimizes,
gcc 4.8 and 5+ is ok with all 3 versions and no ctor and ctor with constexpr
is optimized, gcc 4.9 is unhappy about the no ctor case and happy with the
other two.

> > Especially because 11.x is not going to have the dyninit optimization for
> > sure, it would be nice to do this on the 11 branch too.
> > 
> > 2021-11-04  Jakub Jelinek  <jakub@redhat.com>
> > 
> > 	PR bootstrap/100246
> > 	* config/i386/i386.h
> > 	(stringop_algs::stringop_strategy::stringop_strategy): Make the ctor
> > 	constexpr.
> > 
> > --- gcc/config/i386/i386.h.jj	2021-09-28 23:18:35.282563395 +0200
> > +++ gcc/config/i386/i386.h	2021-11-04 10:48:47.165086806 +0100
> > @@ -78,8 +78,9 @@ struct stringop_algs
> >        this issue.  Since this header is used by code compiled with the C
> >        compiler we must guard the addition.  */
> > #ifdef __cplusplus
> > -    stringop_strategy(int _max = -1, enum stringop_alg _alg = libcall,
> > -		      int _noalign = false)
> > +    constexpr stringop_strategy(int _max = -1,
> > +				enum stringop_alg _alg = libcall,
> > +				int _noalign = false)
> >       : max (_max), alg (_alg), noalign (_noalign) {}
> > #endif
> >     const int max;

	Jakub
  

On Thu, Nov 04, 2021 at 01:45:38PM +0100, Jakub Jelinek via Gcc-patches wrote:
> On Thu, Nov 04, 2021 at 12:39:34PM +0000, Iain Sandoe wrote:
> > Bootstrap succeeded with Apple clang-503.0.40 (Xcode 5.1.1) on macOS 10.8
> > which is the earliest version I expect to work (previous xcode impl. have more
> > C++11 incompatibilities).   So OK from a Darwin PoV.
> > 
> > The other reported toolchain with the issue was GCC-4.9.2 as discussed on
> > IRC - this also seems OK.
> 
> > > Especially because 11.x is not going to have the dyninit optimization for
> > > sure, it would be nice to do this on the 11 branch too.

Bootstrapped/regtested on x86_64-linux and i686-linux successfully too, with
sligtly different formatting, as I think in our coding style constexpr
should go on the previous line and the ctor didn't have space before (.

Ok for trunk and 11.3?

2021-11-05  Jakub Jelinek  <jakub@redhat.com>

	PR bootstrap/100246
	* config/i386/i386.h
	(stringop_algs::stringop_strategy::stringop_strategy): Make the ctor
	constexpr.

--- gcc/config/i386/i386.h.jj	2021-09-28 23:18:35.282563395 +0200
+++ gcc/config/i386/i386.h	2021-11-04 10:48:47.165086806 +0100
@@ -78,8 +78,9 @@ struct stringop_algs
        this issue.  Since this header is used by code compiled with the C
        compiler we must guard the addition.  */
 #ifdef __cplusplus
-    stringop_strategy(int _max = -1, enum stringop_alg _alg = libcall,
-		      int _noalign = false)
+    constexpr
+    stringop_strategy (int _max = -1, enum stringop_alg _alg = libcall,
+		       int _noalign = false)
       : max (_max), alg (_alg), noalign (_noalign) {}
 #endif
     const int max;


	Jakub
  

On Fri, Nov 5, 2021 at 10:59 AM Jakub Jelinek via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> On Thu, Nov 04, 2021 at 01:45:38PM +0100, Jakub Jelinek via Gcc-patches wrote:
> > On Thu, Nov 04, 2021 at 12:39:34PM +0000, Iain Sandoe wrote:
> > > Bootstrap succeeded with Apple clang-503.0.40 (Xcode 5.1.1) on macOS 10.8
> > > which is the earliest version I expect to work (previous xcode impl. have more
> > > C++11 incompatibilities).   So OK from a Darwin PoV.
> > >
> > > The other reported toolchain with the issue was GCC-4.9.2 as discussed on
> > > IRC - this also seems OK.
> >
> > > > Especially because 11.x is not going to have the dyninit optimization for
> > > > sure, it would be nice to do this on the 11 branch too.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux successfully too, with
> sligtly different formatting, as I think in our coding style constexpr
> should go on the previous line and the ctor didn't have space before (.
>
> Ok for trunk and 11.3?

OK.

> 2021-11-05  Jakub Jelinek  <jakub@redhat.com>
>
>         PR bootstrap/100246
>         * config/i386/i386.h
>         (stringop_algs::stringop_strategy::stringop_strategy): Make the ctor
>         constexpr.
>
> --- gcc/config/i386/i386.h.jj   2021-09-28 23:18:35.282563395 +0200
> +++ gcc/config/i386/i386.h      2021-11-04 10:48:47.165086806 +0100
> @@ -78,8 +78,9 @@ struct stringop_algs
>         this issue.  Since this header is used by code compiled with the C
>         compiler we must guard the addition.  */
>  #ifdef __cplusplus
> -    stringop_strategy(int _max = -1, enum stringop_alg _alg = libcall,
> -                     int _noalign = false)
> +    constexpr
> +    stringop_strategy (int _max = -1, enum stringop_alg _alg = libcall,
> +                      int _noalign = false)
>        : max (_max), alg (_alg), noalign (_noalign) {}
>  #endif
>      const int max;
>
>
>         Jakub
>