Re: Test with an lto-build of libgfortran.

[Tobias Burnus <tobias@codesourcery.com>]

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Hi all,

the following works for me. I have only tried a normal build (where it
does silence the same warning) and not an LTO build and I just believed
the comment - see attached patch. Comments?

On 28.09.23 08:25, Richard Biener via Fortran wrote:

> This particular place in libgfortran has
>
>    /* write_z, which calls xtoa_big, is called from transfer.c,
>       formatted_transfer_scalar_write.  There it is passed the kind as
>       argument, which means a maximum of 16.  The buffer is large
>       enough, but the compiler does not know that, so shut up the
>       warning here.  */
> #pragma GCC diagnostic push
> #pragma GCC diagnostic ignored "-Wstringop-overflow"
>    *q = '\0';
> #pragma GCC diagnostic pop
>
> so obviously the #pragma doesn't survive through LTO.  Somehow I think
> this is a known bug, but maybe I misremember (I think we are not streaming
> any of the ad-hoc location parts).

I have replaced it now by the assert that "len <= 16", i.e.

+  if (len > 16)
+    __builtin_unreachable ();

Build + tested on x86-64-gnu-linux
Comment? OK for mainline?

Tobias
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libgfortran: Use __builtin_unreachable() not -Wno-stringop-overflow to silence warning

libgfortran/
	* io/write.c (xtoa_big): Change a 'GCC diagnostic ignored
	"-Wstringop-overflow"' to an assumption (via __builtin_unreachable).

 libgfortran/io/write.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/libgfortran/io/write.c b/libgfortran/io/write.c
index 5d47a6d25f7..00c8fd2e288 100644
--- a/libgfortran/io/write.c
+++ b/libgfortran/io/write.c
@@ -1179,6 +1179,15 @@ xtoa_big (const char *s, char *buffer, int len, GFC_UINTEGER_LARGEST *n)
   uint8_t h, l;
   int i;
 
+  /* write_z, which calls xtoa_big, is called from transfer.c,
+     formatted_transfer_scalar_write.  There it is passed the kind as
+     'len' argument, which means a maximum of 16.  The buffer is large
+     enough, but the compiler does not know that, so shut up the
+     warning here.  */
+
+  if (len > 16)
+    __builtin_unreachable ();
+
   q = buffer;
 
   if (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
@@ -1212,15 +1221,7 @@ xtoa_big (const char *s, char *buffer, int len, GFC_UINTEGER_LARGEST *n)
 	}
     }
 
-  /* write_z, which calls xtoa_big, is called from transfer.c,
-     formatted_transfer_scalar_write.  There it is passed the kind as
-     argument, which means a maximum of 16.  The buffer is large
-     enough, but the compiler does not know that, so shut up the
-     warning here.  */
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wstringop-overflow"
   *q = '\0';
-#pragma GCC diagnostic pop
 
   if (*n == 0)
     return "0";