naruse	2016-02-05 15:52:41 +0900 (Fri, 05 Feb 2016)

  New Revision: 53744

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=53744

  Log:
    improve r53741
    
    * Remove branching by a==0 case
    
    Before r53741:
    % perf stat ./miniruby -e'a=100;i=0;while i<0xfffffff;i+=1;a=(a*557+2)%100000;end'
    
     Performance counter stats for './miniruby -vea=100;i=0;while
    i<0xfffffff;i+=1;a=(a*557+2)%100000;end':
    
          16412.994492 task-clock (msec)         #    0.999 CPUs utilized
                   195 context-switches          #    0.012 K/sec
                     2 cpu-migrations            #    0.000 K/sec
                   876 page-faults               #    0.053 K/sec
           48488588328 cycles                    #    2.954 GHz
           18464835712 stalled-cycles-frontend   #   38.08% frontend cycles
    idle
       <not supported> stalled-cycles-backend
           85665428518 instructions              #    1.77  insns per cycle
                                                 #    0.22  stalled cycles
                                                 #    per insn
           10207419707 branches                  #  621.911 M/sec
               6334713 branch-misses             #    0.06% of all branches
    
          16.426858699 seconds time elapsed
    
    After this:
    % perf stat ./miniruby -ve'a=100;i=0;while i<0xfffffff;i+=1;a=(a*557+2)%100000;end'
    
     Performance counter stats for './miniruby -vea=100;i=0;while i<0xfffffff;i+=1;a=(a*557+2)%100000;end':
    
          13363.540634 task-clock (msec)         #    0.999 CPUs utilized
                   137 context-switches          #    0.010 K/sec
                     2 cpu-migrations            #    0.000 K/sec
                   874 page-faults               #    0.065 K/sec
           39477429278 cycles                    #    2.954 GHz
           14615402375 stalled-cycles-frontend   #   37.02% frontend cycles idle
       <not supported> stalled-cycles-backend
           83514678452 instructions              #    2.12  insns per cycle
                                                 #    0.18  stalled cycles per insn
            9401528135 branches                  #  703.521 M/sec
                432567 branch-misses             #    0.00% of all branches
    
          13.371484310 seconds time elapsed

  Modified files:
    trunk/insns.def
Index: insns.def
===================================================================
--- insns.def	(revision 53743)
+++ insns.def	(revision 53744)
@@ -1431,29 +1431,24 @@ opt_mult https://github.com/ruby/ruby/blob/trunk/insns.def#L1431
     if (FIXNUM_2_P(recv, obj) &&
 	BASIC_OP_UNREDEFINED_P(BOP_MULT, FIXNUM_REDEFINED_OP_FLAG)) {
 	long a = FIX2LONG(recv);
-	if (a == 0) {
-	    val = recv;
-	}
-	else {
 #ifdef HAVE_INT128_T
-	    VALUE rb_int128t2big(int128_t n);
-	    int128_t r = (int128_t)a * FIX2LONG(obj);
-	    if (RB_FIXABLE(r)) {
+	VALUE rb_int128t2big(int128_t n);
+	int128_t r = (int128_t)a * (int128_t)FIX2LONG(obj);
+	if (RB_FIXABLE(r)) {
 		val = LONG2FIX((long)r);
-	    }
-	    else {
+	}
+	else {
 		val = rb_int128t2big(r);
-	    }
+	}
 #else
-	    long b = FIX2LONG(obj);
-	    if (MUL_OVERFLOW_FIXNUM_P(a, b)) {
+	long b = FIX2LONG(obj);
+	if (MUL_OVERFLOW_FIXNUM_P(a, b)) {
 		val = rb_big_mul(rb_int2big(a), rb_int2big(b));
-	    }
-	    else {
+	}
+	else {
 		val = LONG2FIX(a * b);
-	    }
-#endif
 	}
+#endif
     }
     else if (FLONUM_2_P(recv, obj) &&
 	     BASIC_OP_UNREDEFINED_P(BOP_MULT, FLOAT_REDEFINED_OP_FLAG)) {

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