Use carry flag to reduce instructions

NOTE:
(1) Fixnum's LSB is always 1.
    It means you can always run `x - 1` without overflow.
(2) Of course `z = x + (y-1)` may overflow.
    Now z's LSB is always 1, and the MSB of true result is also 1.
    You can get true result in long as `(1<<63)|(z>>1)`,
    and it equals to `(z<<63)|(z>>1)` == `ror(z)`.

GCC and Clang have __builtin_add_ovewflow:
* https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html
* https://clang.llvm.org/docs/LanguageExtensions.html#checked-arithmetic-builtins

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57506 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.in

@@ -2498,6 +2498,9 @@ RUBY_CHECK_BUILTIN_FUNC(__builtin_clzl, [__builtin_clzl(0)])
 RUBY_CHECK_BUILTIN_FUNC(__builtin_clzll, [__builtin_clzll(0)])
 RUBY_CHECK_BUILTIN_FUNC(__builtin_ctz, [__builtin_ctz(0)])
 RUBY_CHECK_BUILTIN_FUNC(__builtin_ctzll, [__builtin_ctzll(0)])
+RUBY_CHECK_BUILTIN_FUNC(__builtin_add_ovewflow, [__builtin_add_ovewflow(0)])
+RUBY_CHECK_BUILTIN_FUNC(__builtin_sub_ovewflow, [__builtin_sub_ovewflow(0)])
+RUBY_CHECK_BUILTIN_FUNC(__builtin_mul_ovewflow, [__builtin_mul_ovewflow(0)])
 RUBY_CHECK_BUILTIN_FUNC(__builtin_constant_p, [__builtin_constant_p(0)])
 RUBY_CHECK_BUILTIN_FUNC(__builtin_choose_expr, [
     [int x[__extension__(__builtin_choose_expr(1, 1, -1))]];

insns.def

@@ -1373,16 +1373,7 @@ opt_plus
 {
     if (FIXNUM_2_P(recv, obj) &&
 	BASIC_OP_UNREDEFINED_P(BOP_PLUS,INTEGER_REDEFINED_OP_FLAG)) {
-	/* fixnum + fixnum */
-#ifndef LONG_LONG_VALUE
-	VALUE msb = (VALUE)1 << ((sizeof(VALUE) * CHAR_BIT) - 1);
-	val = recv - 1 + obj;
-	if ((~(recv ^ obj) & (recv ^ val)) & msb) {
-	    val = rb_int2big((SIGNED_VALUE)((val>>1) | (recv & msb)));
-	}
-#else
-	val = LONG2NUM(FIX2LONG(recv) + FIX2LONG(obj));
-#endif
+	val = rb_fix_plus_fix(recv, obj);
     }
     else if (FLONUM_2_P(recv, obj) &&
 	     BASIC_OP_UNREDEFINED_P(BOP_PLUS, FLOAT_REDEFINED_OP_FLAG)) {
@@ -1426,12 +1417,7 @@ opt_minus
 {
     if (FIXNUM_2_P(recv, obj) &&
 	BASIC_OP_UNREDEFINED_P(BOP_MINUS, INTEGER_REDEFINED_OP_FLAG)) {
-	long a, b, c;
-
-	a = FIX2LONG(recv);
-	b = FIX2LONG(obj);
-	c = a - b;
-	val = LONG2NUM(c);
+	val = rb_fix_minus_fix(recv, obj);
     }
     else if (FLONUM_2_P(recv, obj) &&
 	     BASIC_OP_UNREDEFINED_P(BOP_MINUS, FLOAT_REDEFINED_OP_FLAG)) {

internal.h

@@ -348,6 +348,53 @@ VALUE rb_int128t2big(int128_t n);
 
 #define ST2FIX(h) LONG2FIX((long)(h))
 
+static inline unsigned long
+rb_ulong_rotate_right(unsigned long x)
+{
+    return (x >> 1) | (x << (SIZEOF_LONG * CHAR_BIT - 1));
+}
+
+static inline VALUE
+rb_fix_plus_fix(VALUE x, VALUE y)
+{
+#ifdef HAVE_BUILTIN___BUILTIN_ADD_OVERFLOW
+    long lz;
+    /* NOTE
+     * (1) Fixnum's LSB is always 1.
+     *     It means you can always run `x - 1` without overflow.
+     * (2) Of course `z = x + (y-1)` may overflow.
+     *     Now z's LSB is always 1, and the MSB of true result is also 1.
+     *     You can get true result in long as `(1<<63)|(z>>1)`,
+     *     and it equals to `(z<<63)|(z>>1)` == `ror(z)`.
+     */
+    if (__builtin_add_overflow((long)x, (long)y-1, &lz)) {
+	return rb_int2big(rb_ulong_rotate_right((unsigned long)lz));
+    }
+    else {
+	return (VALUE)lz;
+    }
+#else
+    long lz = FIX2LONG(x) + FIX2LONG(y);
+    return LONG2NUM(lz);
+#endif
+}
+
+static inline VALUE
+rb_fix_minus_fix(VALUE x, VALUE y)
+{
+#ifdef HAVE_BUILTIN___BUILTIN_SUB_OVERFLOW
+    long lz;
+    if (__builtin_sub_overflow((long)x, (long)y-1, &lz)) {
+	return rb_int2big(rb_ulong_rotate_right((unsigned long)lz));
+    }
+    else {
+	return (VALUE)lz;
+    }
+#else
+    long lz = FIX2LONG(x) - FIX2LONG(y);
+    return LONG2NUM(lz);
+#endif
+}
 
 /* arguments must be Fixnum */
 static inline VALUE

numeric.c

@@ -3458,15 +3458,7 @@ static VALUE
 fix_plus(VALUE x, VALUE y)
 {
     if (FIXNUM_P(y)) {
-	long a, b, c;
-	VALUE r;
-
-	a = FIX2LONG(x);
-	b = FIX2LONG(y);
-	c = a + b;
-	r = LONG2NUM(c);
-
-	return r;
+	return rb_fix_plus_fix(x, y);
     }
     else if (RB_TYPE_P(y, T_BIGNUM)) {
 	return rb_big_plus(y, x);
@@ -3513,15 +3505,7 @@ static VALUE
 fix_minus(VALUE x, VALUE y)
 {
     if (FIXNUM_P(y)) {
-	long a, b, c;
-	VALUE r;
-
-	a = FIX2LONG(x);
-	b = FIX2LONG(y);
-	c = a - b;
-	r = LONG2NUM(c);
-
-	return r;
+	return rb_fix_minus_fix(x, y);
     }
     else if (RB_TYPE_P(y, T_BIGNUM)) {
 	x = rb_int2big(FIX2LONG(x));