Re: [PATCH] c++/modules testsuite: avoid expensive ggc-min-expand=0

[Patrick Palka <ppalka@redhat.com>]

On Tue, 23 Apr 2024, Jason Merrill wrote:

> On 4/23/24 11:28, Patrick Palka wrote:
> > Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> 
> Is the test being run for multiple standard levels?  I'd rather restrict it to
> one and keep fully testing GC-safety.

Ah yeah, looks like it runs three times by default, in C++17, C++20 and
C++23 mode.  Like so?  The speedup is almost as good as using
ggc-min-expand=1.

Interestingly, restricting to one standard level _and_ using
ggc-min-expand=1 does not give further speedup.

-- >8 --

Subject: [PATCH] c++/modules testsuite: restrict expensive pr99023 test

The pr99023 testcase uses --param=ggc-min-expand=0 which forces a GC
during every collection point and consequently is very slow to run,
and ends up being the main bottleneck of the modules.exp testsuite.

So this patch restricts this test to run once, in C++20 mode, instead of
multiple times (C++17, C++20 and C++23 mode by default).  After this
patch the modules.exp testsuite finishes in 3m instead of 3m40s with -j8
on my machine.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/pr99023_a.X: Run only in C++20 mode.
	* g++.dg/modules/pr99023_b.X: Likewise.
---
 gcc/testsuite/g++.dg/modules/pr99023_a.X | 1 +
 gcc/testsuite/g++.dg/modules/pr99023_b.X | 1 +
 2 files changed, 2 insertions(+)

diff --git a/gcc/testsuite/g++.dg/modules/pr99023_a.X b/gcc/testsuite/g++.dg/modules/pr99023_a.X
index c872d15f792..507e9569535 100644
--- a/gcc/testsuite/g++.dg/modules/pr99023_a.X
+++ b/gcc/testsuite/g++.dg/modules/pr99023_a.X
@@ -1,4 +1,5 @@
 // PR c++/99023, ICE
+// { dg-require-effective-target c++20_only }
 // { dg-additional-options {-x c++-system-header initializer_list -fmodules-ts --param ggc-min-expand=0} }
 
 // { dg-prune-output {linker input file unused} }
diff --git a/gcc/testsuite/g++.dg/modules/pr99023_b.X b/gcc/testsuite/g++.dg/modules/pr99023_b.X
index ca5f32e5bcc..59d32bee8d5 100644
--- a/gcc/testsuite/g++.dg/modules/pr99023_b.X
+++ b/gcc/testsuite/g++.dg/modules/pr99023_b.X
@@ -1,4 +1,5 @@
 // PR c++/99023, ICE
+// { dg-require-effective-target c++20_only }
 // { dg-additional-options {-x c++-system-header iostream -fmodules-ts -flang-info-include-translate=<initializer_list> --param ggc-min-expand=0} }
 
 // { dg-prune-output {linker input file unused} }
-- 
2.45.0.rc0


> 
> > -- >8 --
> > 
> > The below testcase uses --param=ggc-min-expand=0 which forces a full GC
> > during every collection point and in turn takes over two minutes to run
> > and ends up being the main bottleneck of the modules.exp testsuite.
> > 
> > This patch speeds up this test without (hopefully) significantly affecting
> > its coverage by using =1 instead of =0 which forces a full GC each time the
> > heap grows by 1%, which means exponentially fewer GCs.  After this patch
> > the modules.exp testsuite finishes in 2m55s instead of 3m40s with -j8 on
> > my machine.
> > 
> > gcc/testsuite/ChangeLog:
> > 
> > 	* g++.dg/modules/pr99023_a.X: Use ggc-min-expand=1 instead of =0.
> > 	* g++.dg/modules/pr99023_b.X: Likewise.
> > ---
> >   gcc/testsuite/g++.dg/modules/pr99023_a.X | 2 +-
> >   gcc/testsuite/g++.dg/modules/pr99023_b.X | 2 +-
> >   2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/gcc/testsuite/g++.dg/modules/pr99023_a.X
> > b/gcc/testsuite/g++.dg/modules/pr99023_a.X
> > index c872d15f792..96bb4a2ab5a 100644
> > --- a/gcc/testsuite/g++.dg/modules/pr99023_a.X
> > +++ b/gcc/testsuite/g++.dg/modules/pr99023_a.X
> > @@ -1,5 +1,5 @@
> >   // PR c++/99023, ICE
> > -// { dg-additional-options {-x c++-system-header initializer_list
> > -fmodules-ts --param ggc-min-expand=0} }
> > +// { dg-additional-options {-x c++-system-header initializer_list
> > -fmodules-ts --param ggc-min-expand=1} }
> >     // { dg-prune-output {linker input file unused} }
> >   diff --git a/gcc/testsuite/g++.dg/modules/pr99023_b.X
> > b/gcc/testsuite/g++.dg/modules/pr99023_b.X
> > index ca5f32e5bcc..955378ad88f 100644
> > --- a/gcc/testsuite/g++.dg/modules/pr99023_b.X
> > +++ b/gcc/testsuite/g++.dg/modules/pr99023_b.X
> > @@ -1,5 +1,5 @@
> >   // PR c++/99023, ICE
> > -// { dg-additional-options {-x c++-system-header iostream -fmodules-ts
> > -flang-info-include-translate=<initializer_list> --param ggc-min-expand=0} }
> > +// { dg-additional-options {-x c++-system-header iostream -fmodules-ts
> > -flang-info-include-translate=<initializer_list> --param ggc-min-expand=1} }
> >     // { dg-prune-output {linker input file unused} }
> >   
> 
>