Speed up (+ 2 2) by a factor of 10

Improve arithmetic performance by avoiding bignums until needed.
Also, simplify bignum memory management, fixing some unlikely leaks.
This patch improved the performance of (+ 2 2) by a factor of ten
on a simple microbenchmark computing (+ x 2), byte-compiled,
with x a local variable initialized to 2 via means the byte
compiler could not predict: performance improved from 135 to 13 ns.
The platform was Fedora 28 x86-64, AMD Phenom II X4 910e.
Performance also improved 0.6% on ‘make compile-always’.
* src/bignum.c (init_bignum_once): New function.
* src/emacs.c (main): Use it.
* src/bignum.c (mpz): New global var.
(make_integer_mpz): Rename from make_integer.  All uses changed.
* src/bignum.c (double_to_bignum, make_bignum_bits)
(make_bignum, make_bigint, make_biguint, make_integer_mpz):
* src/data.c (bignum_arith_driver, Frem, Flogcount, Fash)
(expt_integer, Fadd1, Fsub1, Flognot):
* src/floatfns.c (Fabs, rounding_driver, rounddiv_q):
* src/fns.c (Fnthcdr):
Use mpz rather than mpz_initting and mpz_clearing private
temporaries.
* src/bignum.h (bignum_integer): New function.
* src/data.c (Frem, Fmod, Fash, expt_integer):
* src/floatfns.c (rounding_driver):
Use it to simplify code.
* src/data.c (FIXNUMS_FIT_IN_LONG, free_mpz_value):
Remove.  All uses removed.
(floating_point_op): New function.
(floatop_arith_driver): New function, with much of the guts
of the old float_arith_driver.
(float_arith_driver): Use it.
(floatop_arith_driver, arith_driver):
Simplify by assuming NARGS is at least 2.
All callers changed.
(float_arith_driver):
New arg, containing the partly converted value of the next arg.
Reorder args for consistency.  All uses changed.
(bignum_arith_driver): New function.
(arith_driver): Use it.  Do fixnum-only integer calculations
in intmax_t instead of mpz_t, when they fit.
Break out mpz_t calculations into bignum_arith_driver.
(Fquo): Use floatop_arith_driver instead of float_arith_driver,
since the op is known to be valid.
(Flogcount, Fash): Simplify by coalescing bignum and fixnum code.
(Fadd1, Fsub1): Simplify by using make_int.

1 files changed, 13 insertions, 31 deletions

diff --git a/src/floatfns.c b/src/floatfns.c
index 77e20d5640b..2f33b8652b2 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -270,11 +270,8 @@ DEFUN ("abs", Fabs, Sabs, 1, 1, 0,
     {
       if (mpz_sgn (XBIGNUM (arg)->value) < 0)
         {
-          mpz_t val;
-          mpz_init (val);
-          mpz_neg (val, XBIGNUM (arg)->value);
-          arg = make_integer (val);
-          mpz_clear (val);
+          mpz_neg (mpz[0], XBIGNUM (arg)->value);
+          arg = make_integer_mpz ();
         }
     }
 
@@ -360,20 +357,10 @@ rounding_driver (Lisp_Object arg, Lisp_Object divisor,
         {
           if (EQ (divisor, make_fixnum (0)))
             xsignal0 (Qarith_error);
-          mpz_t d, q;
-          mpz_init (d);
-          mpz_init (q);
-          int_divide (q,
-                      (FIXNUMP (arg)
-                       ? (mpz_set_intmax (q, XFIXNUM (arg)), q)
-                       : XBIGNUM (arg)->value),
-                      (FIXNUMP (divisor)
-                       ? (mpz_set_intmax (d, XFIXNUM (divisor)), d)
-                       : XBIGNUM (divisor)->value));
-          Lisp_Object result = make_integer (q);
-          mpz_clear (d);
-          mpz_clear (q);
-          return result;
+          int_divide (mpz[0],
+                      *bignum_integer (&mpz[0], arg),
+                      *bignum_integer (&mpz[1], divisor));
+          return make_integer_mpz ();
         }
 
       double f1 = FLOATP (arg) ? XFLOAT_DATA (arg) : XFIXNUM (arg);
@@ -417,20 +404,15 @@ rounddiv_q (mpz_t q, mpz_t const n, mpz_t const d)
      if (abs_r1 < abs_r + (q & 1))
        q += neg_d == neg_r ? 1 : -1;  */
 
-  mpz_t r, abs_r1;
-  mpz_init (r);
-  mpz_init (abs_r1);
-  mpz_tdiv_qr (q, r, n, d);
+  mpz_t *r = &mpz[2], *abs_r = r, *abs_r1 = &mpz[3];
+  mpz_tdiv_qr (q, *r, n, d);
   bool neg_d = mpz_sgn (d) < 0;
-  bool neg_r = mpz_sgn (r) < 0;
-  mpz_t *abs_r = &r;
-  mpz_abs (*abs_r, r);
-  mpz_abs (abs_r1, d);
-  mpz_sub (abs_r1, abs_r1, *abs_r);
-  if (mpz_cmp (abs_r1, *abs_r) < (mpz_odd_p (q) != 0))
+  bool neg_r = mpz_sgn (*r) < 0;
+  mpz_abs (*abs_r, *r);
+  mpz_abs (*abs_r1, d);
+  mpz_sub (*abs_r1, *abs_r1, *abs_r);
+  if (mpz_cmp (*abs_r1, *abs_r) < (mpz_odd_p (q) != 0))
     (neg_d == neg_r ? mpz_add_ui : mpz_sub_ui) (q, q, 1);
-  mpz_clear (r);
-  mpz_clear (abs_r1);
 }
 
 /* The code uses emacs_rint, so that it works to undefine HAVE_RINT