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

[Jakub Jelinek]

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