cmd/compile: do not escape pure value type on dottype2 conversion

[tshprecher]

1. What version of Go are you using (go version)?

   go version devel +cdcb827 Wed May 18 04:43:32 2016 +0000 darwin/amd64

2. What operating system and processor architecture are you using (go env)?

   GOARCH="amd64"
   GOBIN=""
   GOEXE=""
   GOHOSTARCH="amd64"
   GOHOSTOS="darwin"
   GOOS="darwin"
   GOPATH="/Users/tshprecher/Workspace/go"
   GORACE=""
   GOROOT="/Users/tshprecher/Workspace/golang"
   GOTOOLDIR="/Users/tshprecher/Workspace/golang/pkg/tool/darwin_amd64"
   CC="clang"
   GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -gno-record-gcc-switches -fno-common"
   CXX="clang++"
   CGO_ENABLED="1"

3. What did you do?

   This is a followup to runtime: scalability problem with allocation #13805. I made this fix for the ODOTTYPE node type, but not for ODOTTYPE2.

   input:

   package p
   
   func setPointer(p *int, v interface{}) {
       *p, _ = v.(int)
   }
   
   func main() {
       var i int
       setPointer(&i, 1)
   }
   

4. What did you expect to see?

   dottype_esc.go:9: main 1 does not escape

5. What did you see instead?

   dottype_esc.go:9: 1 escapes to heap

[tshprecher]

sent out for review. complete output for 'go tool compile -m' on the example input above:

dottype_esc.go:3: can inline setPointer
dottype_esc.go:7: can inline main
dottype_esc.go:9: inlining call to setPointer
dottype_esc.go:3: setPointer p does not escape
dottype_esc.go:3: setPointer v does not escape
dottype_esc.go:9: main &i does not escape
dottype_esc.go:9: main 1 does not escape

The int does not escape anymore.

[gopherbot]

CL https://golang.org/cl/24906 mentions this issue.