cmd/compile: fi missing from LHS of fi, err := fs.FileInfo(~R0), ~R1

[nimelehin]

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

$ go version
go version devel go1.17-0613c748e8 Fri Apr 16 14:15:49 2021 +0000 darwin/amd64

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/nikitamelehin/Library/Caches/go-build"
GOENV="/Users/nikitamelehin/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/nikitamelehin/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/nikitamelehin/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/nikitamelehin/Develop/Compiler/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/nikitamelehin/Develop/Compiler/go/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="devel go1.17-0613c748e8 Fri Apr 16 14:15:49 2021 +0000"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/nikitamelehin/Develop/Compiler/go/src/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/0m/jnt6wpss7x50v49qw84c29h40000gn/T/go-build2260580950=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Compiled GO with increased inlineMaxBudged=229. This led to a inlining problem of function func isDir(path string) bool in src/cmd/go/internal/load/pkg.go.

func isDir(path string) bool {
	return isDirCache.Do(path, func() interface{} {
		fi, err := fsys.Stat(path)
		return err == nil && fi.IsDir()
	}).(bool)
}

What did you expect to see?

Successful compilation.

What did you see instead?

Got an error: pkg.go:559:5: internal compiler error: fi missing from LHS of fi, err := fs.FileInfo(~R0), ~R1

[nimelehin]

Is it reasonable to fix that replacing

- if lhs == n {
+ if nlhs, ok := lhs.(*Name); ok && nlhs.Class == n.Class && nlhs.sym == n.sym {
     rhs = defn.Rhs[i]
     break FindRHS
  }

in func staticValue1(nn Node) Node?

[ALTree]

Thanks for reporting this. I'm putting this in the backlog milestone since the crash is only triggered when you change a internal compiler constant (but of course it could be a symptom of a real issue in the inliner code).

cc @dr2chase @mdempsky

[mdempsky]

/cc @danscales for inlining and closures

[randall77]

This doesn't appear to be a problem with the new export/import stuff, as setting go117ExportTypes to false still reproduces.

[mdempsky]

This is the smallest reproducer I've been able to create so far:

package p

func x() {
	var f func()

	func() func() {
		return func() {
			g, _ := f, 0
			g()
		}
	}()()
}

It still requires bumping inlineMaxBudget to at least 83 though.

[mdempsky]

This reproduces with unmodified cmd/compile:

package p

func x() {
	func() func() {
		return func() {
			f := func() {}
			g, _ := f, 0
			g()
		}
	}()()
}

[cuonglm]

@mdempsky seems that we are currently creating new name node for g without modifying new name Defn, so Defn.Lhs still refer to old name node instead of new one.

[mdempsky]

@cuonglm That sounds likely. I took a break from this issue for the moment, so if you want to work on a CL, go for it.

[gopherbot]

Change https://golang.org/cl/312630 mentions this issue: cmd/compile: copy definition node for inline vars