[1/2] MIPS: host_detect_local_cpu, init ret with concat [PR112759]

  The function `reconcat` cannot append string(s) to NULL,
as the concat process will stop at the first NULL.

Let's initialize `ret` with `concat (" ", NULL)`, then
it can be used by reconcat.

gcc/

	PR target/112759
	* config/mips/driver-native.cc (host_detect_local_cpu):
	initialize ret with concat, so that it can be used by
	reconcat later.
---
 gcc/config/mips/driver-native.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
  

On Mon, Dec 18, 2023 at 11:44:21AM +0800, YunQiang Su wrote:
> The function `reconcat` cannot append string(s) to NULL,
> as the concat process will stop at the first NULL.
> 
> Let's initialize `ret` with `concat (" ", NULL)`, then
> it can be used by reconcat.
> 
> gcc/
> 
> 	PR target/112759
> 	* config/mips/driver-native.cc (host_detect_local_cpu):
> 	initialize ret with concat, so that it can be used by
> 	reconcat later.
> ---
>  gcc/config/mips/driver-native.cc | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/gcc/config/mips/driver-native.cc b/gcc/config/mips/driver-native.cc
> index afc276f5278..471d1925eff 100644
> --- a/gcc/config/mips/driver-native.cc
> +++ b/gcc/config/mips/driver-native.cc
> @@ -44,7 +44,7 @@ const char *
>  host_detect_local_cpu (int argc, const char **argv)
>  {
>    const char *cpu = NULL;
> -  char *ret = NULL;
> +  char *ret = concat(" ", NULL);
>    char buf[128];
>    FILE *f;
>    bool arch;
> -- 
> 2.39.2

The formatting is wrong (no space after concat), but more importantly,
I don't think you want to return " " rather than NULL if there isn't
anything known and it is unnecessary to prefix everything with a space
when
gnu-user.h:  " %{march=native:%<march=native %:local_cpu_detect(arch)}"	\
gnu-user.h:  " %{mtune=native:%<mtune=native %:local_cpu_detect(tune)}"
space is already present.  Given the simple thing the function does,
I think much better would be to avoid any reconcat calls and just do one
concat, i.e.
--- gcc/config/mips/driver-native.cc	2023-01-02 09:32:58.422764590 +0100
+++ gcc/config/mips/driver-native.cc	2023-12-18 09:08:39.547609739 +0100
@@ -44,6 +44,7 @@ const char *
 host_detect_local_cpu (int argc, const char **argv)
 {
   const char *cpu = NULL;
+  const char *nan2008 = "";
   char *ret = NULL;
   char buf[128];
   FILE *f;
@@ -90,7 +91,7 @@ host_detect_local_cpu (int argc, const c
 
 fallback_cpu:
 #if defined (__mips_nan2008)
-  ret = reconcat (ret, " -mnan=2008 ", NULL);
+  nan2008 = "-mnan=2008 ";
 #endif
 
 #ifdef HAVE_GETAUXVAL
@@ -104,7 +105,9 @@ fallback_cpu:
 #endif
 
   if (cpu)
-    ret = reconcat (ret, ret, "-m", argv[0], "=", cpu, NULL);
+    ret = concat (nan2008, "-m", argv[0], "=", cpu, NULL);
+  else if (nan2008)
+    ret = concat (nan2008, NULL);
 
   return ret;
 }


Or, if you really want to use reconcat, drop that space from
before -mnan=2008 and use
    ret = reconcat (ret, ret ? ret : "", "-m", argv[0], "=", cpu, NULL);

	Jakub
  

Jakub Jelinek <jakub@redhat.com> 于2023年12月18日周一 16:10写道：
>
> On Mon, Dec 18, 2023 at 11:44:21AM +0800, YunQiang Su wrote:
> > The function `reconcat` cannot append string(s) to NULL,
> > as the concat process will stop at the first NULL.
> >
> > Let's initialize `ret` with `concat (" ", NULL)`, then
> > it can be used by reconcat.
> >
> > gcc/
> >
> >       PR target/112759
> >       * config/mips/driver-native.cc (host_detect_local_cpu):
> >       initialize ret with concat, so that it can be used by
> >       reconcat later.
> > ---
> >  gcc/config/mips/driver-native.cc | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/gcc/config/mips/driver-native.cc b/gcc/config/mips/driver-native.cc
> > index afc276f5278..471d1925eff 100644
> > --- a/gcc/config/mips/driver-native.cc
> > +++ b/gcc/config/mips/driver-native.cc
> > @@ -44,7 +44,7 @@ const char *
> >  host_detect_local_cpu (int argc, const char **argv)
> >  {
> >    const char *cpu = NULL;
> > -  char *ret = NULL;
> > +  char *ret = concat(" ", NULL);
> >    char buf[128];
> >    FILE *f;
> >    bool arch;
> > --
> > 2.39.2
>
> The formatting is wrong (no space after concat), but more importantly,

I will fix the format.

> I don't think you want to return " " rather than NULL if there isn't
> anything known and it is unnecessary to prefix everything with a space
> when
> gnu-user.h:  " %{march=native:%<march=native %:local_cpu_detect(arch)}" \
> gnu-user.h:  " %{mtune=native:%<mtune=native %:local_cpu_detect(tune)}"
> space is already present.  Given the simple thing the function does,
> I think much better would be to avoid any reconcat calls and just do one
> concat, i.e.
> --- gcc/config/mips/driver-native.cc    2023-01-02 09:32:58.422764590 +0100
> +++ gcc/config/mips/driver-native.cc    2023-12-18 09:08:39.547609739 +0100
> @@ -44,6 +44,7 @@ const char *
>  host_detect_local_cpu (int argc, const char **argv)
>  {
>    const char *cpu = NULL;
> +  const char *nan2008 = "";
>    char *ret = NULL;
>    char buf[128];
>    FILE *f;
> @@ -90,7 +91,7 @@ host_detect_local_cpu (int argc, const c
>
>  fallback_cpu:
>  #if defined (__mips_nan2008)
> -  ret = reconcat (ret, " -mnan=2008 ", NULL);
> +  nan2008 = "-mnan=2008 ";
>  #endif
>
>  #ifdef HAVE_GETAUXVAL
> @@ -104,7 +105,9 @@ fallback_cpu:
>  #endif
>
>    if (cpu)
> -    ret = reconcat (ret, ret, "-m", argv[0], "=", cpu, NULL);
> +    ret = concat (nan2008, "-m", argv[0], "=", cpu, NULL);
> +  else if (nan2008)
> +    ret = concat (nan2008, NULL);
>
>    return ret;
>  }
>
>
> Or, if you really want to use reconcat, drop that space from
> before -mnan=2008 and use
>     ret = reconcat (ret, ret ? ret : "", "-m", argv[0], "=", cpu, NULL);
>

Good idea.
Maybe that we can use
ret = reconcat (ret, "-m", argv[0], "=", cpu, ret, NULL);
Then won't worry about ret is NULL here.

One reason I want to use reconcat is that I try to avoid something
wrong in future,
if somebody else add some new detect conditions.
With reconcat, the person will need only copy/paste ;)

It will reduce the possibility for doing something wrong in future.
And let's add a comment here.

>         Jakub
>