[PATCH] libgfortran: Use __builtin_mul_overflow in xmallocarray

[Janne Blomqvist]

As GCC now provides builtins for doing integer overflow checking, lets
use it when checking for overflow in xmallocarray.

Regtested on x86_64-pc-linux-gnu, Ok for trunk?

libgfortran/ChangeLog:

2019-06-14  Janne Blomqvist  <j...@gcc.gnu.org>

        * runtime/memory.c (SIZE_MAX):Remove macro definition.
        (xmallocarray): Use __builtin_mul_overflow.
---
 libgfortran/runtime/memory.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/libgfortran/runtime/memory.c b/libgfortran/runtime/memory.c
index 1a3d33b59dd..09a4ff8733f 100644
--- a/libgfortran/runtime/memory.c
+++ b/libgfortran/runtime/memory.c
@@ -26,10 +26,6 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If 
not, see
 #include "libgfortran.h"
 #include <errno.h>
 
-#ifndef SIZE_MAX
-#define SIZE_MAX ((size_t)-1)
-#endif
-
 
 void *
 xmalloc (size_t n)
@@ -52,18 +48,17 @@ void *
 xmallocarray (size_t nmemb, size_t size)
 {
   void *p;
+  size_t prod;
 
   if (!nmemb || !size)
-    size = nmemb = 1;
-#define HALF_SIZE_T (((size_t) 1) << (__CHAR_BIT__ * sizeof (size_t) / 2))
-  else if (__builtin_expect ((nmemb | size) >= HALF_SIZE_T, 0)
-          && nmemb > SIZE_MAX / size)
+    prod = 1;
+  else if (__builtin_mul_overflow (nmemb, size, &prod))
     {
       errno = ENOMEM;
       os_error ("Integer overflow in xmallocarray");
     }
 
-  p = malloc (nmemb * size);
+  p = malloc (prod);
 
   if (!p)
     os_error ("Memory allocation failed in xmallocarray");
-- 
2.17.1