| Message ID | 87li07s0um.fsf@talisman.default |
|---|---|
| State | New |
| Headers | show |
Richard Sandiford <rdsandiford@googlemail.com> wrote: >Richard Biener <richard.guenther@gmail.com> writes: >> On Fri, Nov 29, 2013 at 12:14 PM, Richard Sandiford >> <rdsandiford@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? Ok. I assume we already have a special.case for division by 1? Thanks, Richard. >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. */
Richard Biener <richard.guenther@gmail.com> writes: > Richard Sandiford <rdsandiford@googlemail.com> wrote: >>Richard Biener <richard.guenther@gmail.com> writes: >>> On Fri, Nov 29, 2013 at 12:14 PM, Richard Sandiford >>> <rdsandiford@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? > > Ok. I assume we already have a special.case for division by 1? I don't think it's really worth having one there. If the inputs fit into single HWIs then the output does too, so we can just use a host division. 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. */