Richard Biener <[email protected]> writes:
> On Fri, Nov 29, 2013 at 12:14 PM, Richard Sandiford
> <[email protected]> wrote:
>> In the fold-const.ii testcase, well over half of the mul_internal calls
>> were for multiplication by 0 (106038 out of 169355). This patch adds
>> an early-out for that.
>>
>> Tested on x86_64-linux-gnu. OK to install?
>
> Ok. Did you check how many of the remaining are multiplies by 1?
Turns out to be 9685, which is probably enough to justify a special case.
Tested on x86_64-linux-gnu. OK to install?
Thanks,
Richard
Index: gcc/wide-int.cc
===================================================================
--- gcc/wide-int.cc 2013-11-29 15:04:41.177142418 +0000
+++ gcc/wide-int.cc 2013-11-29 15:05:36.482424592 +0000
@@ -1296,6 +1296,20 @@ wi::mul_internal (HOST_WIDE_INT *val, co
return 1;
}
+ /* Handle multiplications by 1. */
+ if (op1len == 1 && op1[0] == 1)
+ {
+ for (i = 0; i < op2len; i++)
+ val[i] = op2[i];
+ return op2len;
+ }
+ if (op2len == 1 && op2[0] == 1)
+ {
+ for (i = 0; i < op1len; i++)
+ val[i] = op1[i];
+ return op1len;
+ }
+
/* If we need to check for overflow, we can only do half wide
multiplies quickly because we need to look at the top bits to
check for the overflow. */
