I imagine the new SSA backend can do this with its pattern matching, but you would need to look for it here:
https://github.com/golang/go/blob/master/src/cmd/compile/internal/ssa/gen/generic.rules or https://github.com/golang/go/blob/master/src/cmd/compile/internal/ssa/gen/AMD64.rules Maybe someone else can confirm. On Tuesday, November 8, 2016 at 6:18:02 PM UTC+13, ra...@cockroachlabs.com wrote: > > Sorry to revive an old thread. One thing to note is that dividing a > 64-bit by a 32-bit is much faster than dividing a 64-bit by a 64-bit, at > least on recent Intel platforms. Unfortunately there is no valid way to > express that kind of calculation in Go.. > > Is the compiler/optimizer smart enough to figure out it can do that if you > do something like `uint32(a / uint64(b))` where a is `uint64` and b is > `uint32`? (the result of that expression can be computed using the 32-bit > version of DIV) > > On Saturday, January 19, 2013 at 6:10:34 PM UTC-5, Michael Jones wrote: >> >> Integer division is slow. >> >> It is the unloved arithmetic operation in CPU design because of its low >> frequency of occurrence in the instruction stream. It is the one--if you >> remember childhood schooling--that was "not like the others" in its >> mechanism: there was lots of guessing using leading digits, trial divisors, >> and so on. This awkwardness exists even in base 2 (though much less) and >> means that any division circuit my have to do at least one "fixup" step. (A >> good design does either zero or one fixup, but that one means more work and >> plausibly an extra cycle on what is already a long cycle-count activity.) >> >> As one specific example, when adding and subtracting were 1 cycle and >> multiply was 4, a 32-bit integer division required 19 cycles. >> >> >> On Sat, Jan 19, 2013 at 1:25 PM, minux <minu...@gmail.com> wrote: >> >>> >>> >>> On Sun, Jan 20, 2013 at 5:22 AM, Jan Mercl <0xj...@gmail.com> wrote: >>> >>>> On Sat, Jan 19, 2013 at 10:13 PM, Dominik Honnef <domi...@fork-bomb.org> >>>> wrote: >>>> >>>> Cannot reproduce here (Xeon on dont-know-how-much GHz) >>>> >>>> jnml@fsc-r630:~/src/tmp/20130119$ cat a_test.go >>>> package main >>>> >>>> import ( >>>> "testing" >>>> ) >>>> >>>> func BenchmarkBase(b *testing.B) { >>>> var x int32 >>>> for i := 1; i < b.N; i++ { >>>> } >>>> _ = x >>>> } >>>> >>>> func BenchmarkInt(b *testing.B) { >>>> var x int >>>> for i := 1; i < b.N; i++ { >>>> x /= 42 >>>> } >>>> _ = x >>>> } >>>> >>> division by a constant should be turned into multiplication by magic >>> constants >>> by the Go compiler just to avoid the costly divide instruction. >>> >>> you can verify that by 'go tool 6g -S'. >>> >>> -- >>> >>> >>> >> >> >> >> -- >> Michael T. Jones | Chief Technology Advocate | m...@google.com | +1 >> 650-335-5765 >> > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
