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, 18 insertions, 1 deletions

diff --git a/src/bignum.h b/src/bignum.h
index a368333d77e..07622a37af4 100644
--- a/src/bignum.h
+++ b/src/bignum.h
@@ -41,7 +41,10 @@ struct Lisp_Bignum
   mpz_t value;
 };
 
-extern Lisp_Object make_integer (mpz_t const) ARG_NONNULL ((1));
+extern mpz_t mpz[4];
+
+extern void init_bignum_once (void);
+extern Lisp_Object make_integer_mpz (void);
 extern void mpz_set_intmax_slow (mpz_t, intmax_t) ARG_NONNULL ((1));
 
 INLINE_HEADER_BEGIN
@@ -65,6 +68,20 @@ mpz_set_intmax (mpz_t result, intmax_t v)
     mpz_set_intmax_slow (result, v);
 }
 
+/* Return a pointer to an mpz_t that is equal to the Lisp integer I.
+   If I is a bignum this returns a pointer to I's representation;
+   otherwise this sets *TMP to I's value and returns TMP.  */
+INLINE mpz_t *
+bignum_integer (mpz_t *tmp, Lisp_Object i)
+{
+  if (FIXNUMP (i))
+    {
+      mpz_set_intmax (*tmp, XFIXNUM (i));
+      return tmp;
+    }
+  return &XBIGNUM (i)->value;
+}
+
 INLINE_HEADER_END
 
 #endif /* BIGNUM_H */