Patchwork [c++] Stop in cp_write_global_declarations after writing a PCH

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Submitter Steven Bosscher
Date Dec. 2, 2012, 8:27 p.m.
Message ID <CABu31nPdef8OphA=G-=YnfmcKPontAeONfv-b3w=pu8GunPTVg@mail.gmail.com>
Download mbox | patch
Permalink /patch/203251/
State New
Headers show

Comments

Steven Bosscher - Dec. 2, 2012, 8:27 p.m.
Hello,

The C++ front end pushes everything through the compiler queue after
writing a PCH. This is pointless: After the PCH is written nothing the
compiler does has any effect on it anymore.

This patch makes the C++ front end stop after writing the PCH,
speeding up PCH creation

The C front end has behaved this way since 2004
(http://gcc.gnu.org/ml/gcc-patches/2004-07/msg00738.html).

Bootstrapped&tested on powerpc64-unknown-linux-gnu and x86_64-unknown-linux-gnu.
OK for trunk?

Ciao!
Steven



        * decl2.c (cp_write_global_declarations): Return after writing a PCH.




Compile time at -O2 (test = patched, orig = unpatched):
$ for i in 1 2 3 ; do time ~/devel/build-test/gcc/xg++
-B../devel/build-test/gcc/ -w -O2 slow.h ; done ; ls -ltr

real    0m8.577s
user    0m8.037s
sys     0m0.540s

real    0m8.580s
user    0m8.093s
sys     0m0.484s

real    0m8.595s
user    0m8.093s
sys     0m0.500s
total 100440
-rw-r--r-- 1 stevenb stevenb  4017783 2012-12-02 21:16 slow.h
-rw-r--r-- 1 stevenb stevenb 98722192 2012-12-02 21:20 slow.h.gch
$ for i in 1 2 3 ; do time ~/devel/build-orig/gcc/xg++
-B../devel/build-orig/gcc/ -w -O2 slow.h ; done ; ls -ltr

real    0m10.795s
user    0m10.273s
sys     0m0.520s

real    0m10.876s
user    0m10.365s
sys     0m0.544s

real    0m10.767s
user    0m10.245s
sys     0m0.520s
total 100440
-rw-r--r-- 1 stevenb stevenb  4017783 2012-12-02 21:16 slow.h
-rw-r--r-- 1 stevenb stevenb 98722192 2012-12-02 21:20 slow.h.gch
Steven Bosscher - Dec. 7, 2012, 9:52 a.m.
Ping?

On Sun, Dec 2, 2012 at 9:27 PM, Steven Bosscher wrote:
> Hello,
>
> The C++ front end pushes everything through the compiler queue after
> writing a PCH. This is pointless: After the PCH is written nothing the
> compiler does has any effect on it anymore.
>
> This patch makes the C++ front end stop after writing the PCH,
> speeding up PCH creation
>
> The C front end has behaved this way since 2004
> (http://gcc.gnu.org/ml/gcc-patches/2004-07/msg00738.html).
>
> Bootstrapped&tested on powerpc64-unknown-linux-gnu and x86_64-unknown-linux-gnu.
> OK for trunk?
>
> Ciao!
> Steven
>
>
>
>         * decl2.c (cp_write_global_declarations): Return after writing a PCH.
>
> Index: decl2.c
> ===================================================================
> --- decl2.c     (revision 194052)
> +++ decl2.c     (working copy)
> @@ -3944,8 +3944,13 @@ cp_write_global_declarations (void)
>        || !vec_safe_is_empty (decl_namespace_list))
>      return;
>
> +  /* This is the point to write out a PCH if we're doing that.
> +     In that case we do not want to do anything else.  */
>    if (pch_file)
> -    c_common_write_pch ();
> +    {
> +      c_common_write_pch ();
> +      return;
> +    }
>
>    cgraph_process_same_body_aliases ();
>
>
>
>
> Compile time at -O2 (test = patched, orig = unpatched):
> $ for i in 1 2 3 ; do time ~/devel/build-test/gcc/xg++
> -B../devel/build-test/gcc/ -w -O2 slow.h ; done ; ls -ltr
>
> real    0m8.577s
> user    0m8.037s
> sys     0m0.540s
>
> real    0m8.580s
> user    0m8.093s
> sys     0m0.484s
>
> real    0m8.595s
> user    0m8.093s
> sys     0m0.500s
> total 100440
> -rw-r--r-- 1 stevenb stevenb  4017783 2012-12-02 21:16 slow.h
> -rw-r--r-- 1 stevenb stevenb 98722192 2012-12-02 21:20 slow.h.gch
> $ for i in 1 2 3 ; do time ~/devel/build-orig/gcc/xg++
> -B../devel/build-orig/gcc/ -w -O2 slow.h ; done ; ls -ltr
>
> real    0m10.795s
> user    0m10.273s
> sys     0m0.520s
>
> real    0m10.876s
> user    0m10.365s
> sys     0m0.544s
>
> real    0m10.767s
> user    0m10.245s
> sys     0m0.520s
> total 100440
> -rw-r--r-- 1 stevenb stevenb  4017783 2012-12-02 21:16 slow.h
> -rw-r--r-- 1 stevenb stevenb 98722192 2012-12-02 21:20 slow.h.gch
Richard Guenther - Dec. 7, 2012, 2:13 p.m.
On Fri, Dec 7, 2012 at 10:52 AM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
> Ping?

Ok if C++ frontend maintainers don't complain over the weekend.

Thanks,
Richard.

> On Sun, Dec 2, 2012 at 9:27 PM, Steven Bosscher wrote:
>> Hello,
>>
>> The C++ front end pushes everything through the compiler queue after
>> writing a PCH. This is pointless: After the PCH is written nothing the
>> compiler does has any effect on it anymore.
>>
>> This patch makes the C++ front end stop after writing the PCH,
>> speeding up PCH creation
>>
>> The C front end has behaved this way since 2004
>> (http://gcc.gnu.org/ml/gcc-patches/2004-07/msg00738.html).
>>
>> Bootstrapped&tested on powerpc64-unknown-linux-gnu and x86_64-unknown-linux-gnu.
>> OK for trunk?
>>
>> Ciao!
>> Steven
>>
>>
>>
>>         * decl2.c (cp_write_global_declarations): Return after writing a PCH.
>>
>> Index: decl2.c
>> ===================================================================
>> --- decl2.c     (revision 194052)
>> +++ decl2.c     (working copy)
>> @@ -3944,8 +3944,13 @@ cp_write_global_declarations (void)
>>        || !vec_safe_is_empty (decl_namespace_list))
>>      return;
>>
>> +  /* This is the point to write out a PCH if we're doing that.
>> +     In that case we do not want to do anything else.  */
>>    if (pch_file)
>> -    c_common_write_pch ();
>> +    {
>> +      c_common_write_pch ();
>> +      return;
>> +    }
>>
>>    cgraph_process_same_body_aliases ();
>>
>>
>>
>>
>> Compile time at -O2 (test = patched, orig = unpatched):
>> $ for i in 1 2 3 ; do time ~/devel/build-test/gcc/xg++
>> -B../devel/build-test/gcc/ -w -O2 slow.h ; done ; ls -ltr
>>
>> real    0m8.577s
>> user    0m8.037s
>> sys     0m0.540s
>>
>> real    0m8.580s
>> user    0m8.093s
>> sys     0m0.484s
>>
>> real    0m8.595s
>> user    0m8.093s
>> sys     0m0.500s
>> total 100440
>> -rw-r--r-- 1 stevenb stevenb  4017783 2012-12-02 21:16 slow.h
>> -rw-r--r-- 1 stevenb stevenb 98722192 2012-12-02 21:20 slow.h.gch
>> $ for i in 1 2 3 ; do time ~/devel/build-orig/gcc/xg++
>> -B../devel/build-orig/gcc/ -w -O2 slow.h ; done ; ls -ltr
>>
>> real    0m10.795s
>> user    0m10.273s
>> sys     0m0.520s
>>
>> real    0m10.876s
>> user    0m10.365s
>> sys     0m0.544s
>>
>> real    0m10.767s
>> user    0m10.245s
>> sys     0m0.520s
>> total 100440
>> -rw-r--r-- 1 stevenb stevenb  4017783 2012-12-02 21:16 slow.h
>> -rw-r--r-- 1 stevenb stevenb 98722192 2012-12-02 21:20 slow.h.gch
Steven Bosscher - Dec. 10, 2012, 6 p.m.
On Fri, Dec 7, 2012 at 3:13 PM, Richard Biener wrote:
> On Fri, Dec 7, 2012 at 10:52 AM, Steven Bosscher wrote:
>> Ping?
>
> Ok if C++ frontend maintainers don't complain over the weekend.

Committed now.
BTW I forgot to mention I also did a build+test with this patch and
with gcac checking enabled.

Ciao!
Steven

Patch

Index: decl2.c
===================================================================
--- decl2.c     (revision 194052)
+++ decl2.c     (working copy)
@@ -3944,8 +3944,13 @@  cp_write_global_declarations (void)
       || !vec_safe_is_empty (decl_namespace_list))
     return;

+  /* This is the point to write out a PCH if we're doing that.
+     In that case we do not want to do anything else.  */
   if (pch_file)
-    c_common_write_pch ();
+    {
+      c_common_write_pch ();
+      return;
+    }

   cgraph_process_same_body_aliases ();