Tally GMP allocations

Without this, bignum allocations in the pidigits don't properly trigger
GC.  This patch changes the peak memory usage for the pidigits benchmark
by a factor of 6.  The benchmark also begins to spend much more time in
GC, as it should be:

|        | max rss   | elapsed time |
|--------+-----------+--------------|
| before | 392472 KB | 6.7 s        |
| after  | 58512 KB  | 32.93 s      |

* src/bignum.h (init_gmp_memory_functions): Declare new function.
* src/alloc.c (init_gmp_memory_functions): Implement it.
(xmalloc_for_gmp): New helper.
(xrealloc_for_gmp, xfree_for_gmp): Moved here from bignum.c.
* src/bignum.c (init_bignum): Call init_gmp_memory_functions.

src/alloc.c

@@ -2600,6 +2600,42 @@ make_float (double float_value)
 #endif
 }
 
+
+static void *
+xmalloc_for_gmp (size_t size)
+{
+  tally_consing (size);
+  return xmalloc (size);
+}
+
+static void *
+xrealloc_for_gmp (void *ptr, size_t old_size, size_t new_size)
+{
+  tally_consing (new_size - old_size);
+  return xrealloc (ptr, new_size);
+}
+
+static void
+xfree_for_gmp (void *ptr, size_t size)
+{
+  tally_consing (-size);
+  xfree (ptr);
+}
+
+void
+init_gmp_memory_functions (void)
+{
+  /* FIXME: The Info node `(gmp) Custom Allocation' states: "No error
+     return is allowed from any of these functions, if they return
+     then they must have performed the specified operation. [...]
+       There's currently no defined way for the allocation functions
+     to recover from an error such as out of memory, they must
+     terminate program execution.  A 'longjmp' or throwing a C++
+     exception will have undefined results."  But xmalloc and xrealloc
+     do call 'longjmp'.  */
+  mp_set_memory_functions (xmalloc_for_gmp, xrealloc_for_gmp,
+			   xfree_for_gmp);
+}
 
 
 /***********************************************************************

src/bignum.c

@@ -36,33 +36,13 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 
 mpz_t mpz[5];
 
-static void *
-xrealloc_for_gmp (void *ptr, size_t ignore, size_t size)
-{
-  return xrealloc (ptr, size);
-}
-
-static void
-xfree_for_gmp (void *ptr, size_t ignore)
-{
-  xfree (ptr);
-}
-
 void
 init_bignum (void)
 {
   eassert (mp_bits_per_limb == GMP_NUMB_BITS);
   integer_width = 1 << 16;
 
-  /* FIXME: The Info node `(gmp) Custom Allocation' states: "No error
-     return is allowed from any of these functions, if they return
-     then they must have performed the specified operation. [...]
-     There's currently no defined way for the allocation functions to
-     recover from an error such as out of memory, they must terminate
-     program execution.  A 'longjmp' or throwing a C++ exception will
-     have undefined results."  But xmalloc and xrealloc do call
-     'longjmp'.  */
-  mp_set_memory_functions (xmalloc, xrealloc_for_gmp, xfree_for_gmp);
+  init_gmp_memory_functions ();
 
   for (int i = 0; i < ARRAYELTS (mpz); i++)
     mpz_init (mpz[i]);

src/bignum.h

@@ -59,6 +59,9 @@ extern void emacs_mpz_pow_ui (mpz_t, mpz_t const, unsigned long)
 extern double mpz_get_d_rounded (mpz_t const);
 extern Lisp_Object get_random_bignum (struct Lisp_Bignum const *);
 
+/* defined in alloc.c  */
+extern void init_gmp_memory_functions (void);
+
 INLINE_HEADER_BEGIN
 
 INLINE struct Lisp_Bignum *