Closed
Description
What version of Go are you using (go version)?
$ go version go version devel +0377f06168 Tue Dec 17 20:57:06 2019 +0000 windows/amd64
Does this issue reproduce with the latest release?
Yes
What operating system and processor architecture are you using (go env)?
go env Output
$ go env set GO111MODULE=auto set GOARCH=amd64 set GOBIN= set GOCACHE=C:\Users\mattn\AppData\Local\go-build set GOENV=C:\Users\mattn\AppData\Roaming\go\env set GOEXE=.exe set GOFLAGS= set GOHOSTARCH=amd64 set GOHOSTOS=windows set GOINSECURE= set GONOPROXY= set GONOSUMDB= set GOOS=windows set GOPATH=C:\Users\mattn\go set GOPRIVATE= set GOPROXY=https://proxy.golang.org,direct set GOROOT=C:\go set GOSUMDB=sum.golang.org set GOTMPDIR= set GOTOOLDIR=C:\go\pkg\tool\windows_amd64 set GCCGO=gccgo set AR=ar set CC=gcc set CXX=g++ set CGO_ENABLED=1 set GOMOD= set CGO_CFLAGS=-g -O2 set CGO_CPPFLAGS= set CGO_CXXFLAGS=-g -O2 set CGO_FFLAGS=-g -O2 set CGO_LDFLAGS=-g -O2 set PKG_CONFIG=pkg-config set GOGCCFLAGS=-m64 -mthreads -fmessage-length=0 -fdebug-prefix-map=C:\Users\mattn\AppData\Local\Temp\go-build216348474=/tmp/go-build -gno-record-gcc-switches
What did you do?
package main
import (
"fmt"
"math"
"math/rand"
"time"
)
var a, b, c, d float64
func pure_fma_func() {
d = math.FMA(a, b, c)
}
func non_fma_func() {
d = a*b + c
}
func main() {
const n = 1000000000
a = rand.Float64()
b = rand.Float64()
c = rand.Float64()
t1 := time.Now()
for i := int64(0); i < n; i++ {
non_fma_func()
}
t2 := time.Now()
for i := int64(0); i < n; i++ {
pure_fma_func()
}
t3 := time.Now()
fmt.Println("non FMA", t2.Sub(t1))
fmt.Println(" FMA", t3.Sub(t2))
}And go run.
What did you expect to see?
math.FMA is faster than non-FMA code.
What did you see instead?
non FMA 548.0314ms
FMA 924.0528ms
I confirmed my CPU have simd-FMA. Is this an overhead of function call?