Richard Biener <richard.guent...@gmail.com> writes: > On Fri, Nov 29, 2013 at 12:14 PM, Richard Sandiford > <rdsandif...@googlemail.com> 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. */