1. What version of Go are you using (go version)?
   go version devel +ac47f66 Tue Mar 15 07:13:04 2016 +0000 linux/amd64
2. What operating system and processor architecture are you using (go env)?
   Ubuntu 14.04 in Intel(R) Core(TM) i5-2450M CPU @ 2.50GHz
   GOARCH="amd64"
   GOBIN=""
   GOEXE=""
   GOHOSTARCH="amd64"
   GOHOSTOS="linux"
   GOOS="linux"
   GOPATH="/home/i/go"
   GORACE=""
   GOROOT="/home/i/gotip"
   GOTOOLDIR="/home/i/gotip/pkg/tool/linux_amd64"
   CC="gcc"
   GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build380342597=/tmp/go-build -gno-record-gcc-switches"
   CXX="g++"
   CGO_ENABLED="1"
3. What did you do?
   Code is at http://play.golang.org/p/L8SlHM5_IJ

It contains benchmark for two functions that average a []float64, one using index in the range-for and other using the value.

I run it with

go test -bench=.

I'm getting a performance regression for tip with SSA on for the value case.

go1.4.3:
BenchmarkAvgSliceValue 500 3815534 ns/op
BenchmarkAvgSliceIndex 300 5028982 ns/op

go1.5.3:
BenchmarkAvgSliceValue-4 500 3768664 ns/op
BenchmarkAvgSliceIndex-4 300 5030110 ns/op

go1.6:
BenchmarkAvgSliceValue-4 500 3769454 ns/op
BenchmarkAvgSliceIndex-4 300 5026162 ns/op

go-tip with ssa off and checks off:
~/gotip/bin/go test -bench=. -gcflags='-d=ssa/check/off -ssa=0'
BenchmarkAvgSliceValue-4 500 3771890 ns/op
BenchmarkAvgSliceIndex-4 300 5030560 ns/op

go-tip with ssa on and checks off:
~/gotip/bin/go test -bench=. -gcflags='-d=ssa/check/off -ssa=1'
BenchmarkAvgSliceValue-4 300 5028224 ns/op
BenchmarkAvgSliceIndex-4 300 5025677 ns/op

1. What did you expect to see?
   Similar performance with SSA on.
2. What did you see instead?
   Compiling with SSA produces a 25% slowdown when the value is used. Disabling consistency checks doesn't help but I think it just for compiling. It seems that some optimizations for value range loop are not being applied in SSA.

The slowdown is so large for this function that I suspect I'm doing something wrong or there are some other checks in the SSA compiled code that I'm not disabling.