On 4/22/21 10:04 AM, Richard Biener wrote:
> On Wed, Apr 21, 2021 at 3:08 PM Martin Liška <mli...@suse.cz> wrote:
>>
>> When -flto=jobserver is used and we cannot detect job server, then we can
>> still fallbackto -flto=N mode.
>>
>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
>>
>> Ready to be installed?
>
> I think this behavior needs to be documented - it falls back to a less
> conservative (possibly system overloading) mode - which IMHO is
> non-obvious and IMHO we shouldn't do.
Sure, I'm sending corresponding patch. Note that it's quite common mistake
that '+' is missing in Makefile rule. That was motivation for my change.
Martin
>
> Richard.
>
>> Thanks,
>> Martin
>>
>> gcc/ChangeLog:
>>
>> * lto-wrapper.c (run_gcc): When -flto=jobserver is used, but the
>> makeserver cannot be detected, then use -flto=N fallback.
>> ---
>> gcc/lto-wrapper.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/gcc/lto-wrapper.c b/gcc/lto-wrapper.c
>> index 03a5922f8ea..0b626d7c811 100644
>> --- a/gcc/lto-wrapper.c
>> +++ b/gcc/lto-wrapper.c
>> @@ -1585,8 +1585,9 @@ run_gcc (unsigned argc, char *argv[])
>> if (jobserver && jobserver_error != NULL)
>> {
>> warning (0, jobserver_error);
>> - parallel = 0;
>> + /* Fall back to auto parallelism. */
>> jobserver = 0;
>> + auto_parallel = 1;
>> }
>> else if (!jobserver && jobserver_error == NULL)
>> {
>> --
>> 2.31.1
>>
>From b81f5288fc81256e63d44e00793e2732eb2a2d88 Mon Sep 17 00:00:00 2001
From: Martin Liska <mli...@suse.cz>
Date: Thu, 22 Apr 2021 10:59:51 +0200
Subject: [PATCH] Document -flto=jobserver fallback.
gcc/ChangeLog:
* doc/invoke.texi: Document what happens when GCC can't detect
make's job server with -flto=jobserver.
---
gcc/doc/invoke.texi | 3 +++
1 file changed, 3 insertions(+)
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index e98b0962b9f..1cfff4c14a9 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -12340,6 +12340,9 @@ Use @option{-flto=auto} to use GNU make's job server, if available,
or otherwise fall back to autodetection of the number of CPU threads
present in your system.
+If you specify @option{-flto=jobserver} and make's job server can't be detected,
+then well fall back to the number of CPU threads present in your system.
+
@item -flto-partition=@var{alg}
@opindex flto-partition
Specify the partitioning algorithm used by the link-time optimizer.
--
2.31.1
