cmd/compile: gotip internal compiler error: shape types have no methods .shape.string_0

[inso]

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

$ gotip version
go version devel go1.18-519c0a2 Wed Nov 3 05:00:00 2021 +0000 linux/amd64

What did you do?

$ cat issue.go 
package main

func test[T any](f func (c T)) {
	var r T

	f(r)
}

func test2(a ...interface{}) {
}

func main() {
	test(func(c string) { test2(c) })
}

$ gotip build issue.go

What did you expect to see?

Successful compilation

What did you see instead?

# command-line-arguments
./issue.go:13:6: internal compiler error: shape types have no methods .shape.string_0

goroutine 1 [running]:
runtime/debug.Stack()
	/home/inso/sdk/gotip/src/runtime/debug/stack.go:24 +0x65
cmd/compile/internal/base.FatalfAt({0xce818?, 0xc0?}, {0xd2377b, 0x1f}, {0xc0000ce808, 0x1, 0x1})
	/home/inso/sdk/gotip/src/cmd/compile/internal/base/print.go:227 +0x1ca
cmd/compile/internal/base.Fatalf(...)
	/home/inso/sdk/gotip/src/cmd/compile/internal/base/print.go:196
cmd/compile/internal/reflectdata.MarkTypeUsedInInterface(0xc0003dc690, 0xc0000f5380)
	/home/inso/sdk/gotip/src/cmd/compile/internal/reflectdata/reflect.go:1979 +0x6f
cmd/compile/internal/walk.walkConvInterface(0xc0003db900, 0xc0000ceea0)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/convert.go:49 +0x107
cmd/compile/internal/walk.walkExpr1({0xe81e50, 0xc0003db900}, 0xc0003db900?)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/expr.go:211 +0x57f
cmd/compile/internal/walk.walkExpr({0xe81e50, 0xc0003db900}, 0xc0000ceea0)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/expr.go:55 +0x428
cmd/compile/internal/walk.walkAssign(0xc0000ceea0, {0xe814f0, 0xc0005605a0?})
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/assign.go:72 +0x9dc
cmd/compile/internal/walk.walkExpr1({0xe814f0, 0xc0005605a0}, 0xc0005605a0?)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/expr.go:179 +0x43f
cmd/compile/internal/walk.walkExpr({0xe814f0, 0xc0005605a0}, 0xc0000ceea0)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/expr.go:55 +0x428
cmd/compile/internal/walk.walkStmt({0xe814f0, 0xc0005605a0?})
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/stmt.go:57 +0x7da
cmd/compile/internal/walk.walkStmtList(...)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/stmt.go:175
cmd/compile/internal/walk.walkStmt({0xe81748, 0xc000568200?})
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/stmt.go:98 +0xe3c
cmd/compile/internal/walk.slicelit(0x0, 0xc0000f4900, {0xe82eb8?, 0xc0003e25b0}, 0xc0000cf6d8)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/complit.go:405 +0xc6d
cmd/compile/internal/walk.anylit({0xe81cc0, 0xc0000f4900}, {0xe82eb8?, 0xc0003e25b0}, 0xc000546680?)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/complit.go:592 +0x4c5
cmd/compile/internal/walk.oaslit(0xc000560370, 0xc0003e25b0?)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/complit.go:635 +0x198
cmd/compile/internal/walk.walkAssign(0xc0000cf6d8, {0xe814f0, 0xc000560370?})
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/assign.go:57 +0x5eb
cmd/compile/internal/walk.walkExpr1({0xe814f0, 0xc000560370}, 0xc000560370?)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/expr.go:179 +0x43f
cmd/compile/internal/walk.walkExpr({0xe814f0, 0xc000560370}, 0xc0000cf6d8)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/expr.go:55 +0x428
cmd/compile/internal/walk.appendWalkStmt(0xc0000cf6d8, {0xe814f0, 0xc000560370})
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/walk.go:256 +0x65
cmd/compile/internal/walk.ascompatee(0x16, {0xc00009f1f0?, 0x1, 0x1?}, {0xc00009f1d0, 0x1, 0x7f3a0419c600?})
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/assign.go:372 +0x6eb
cmd/compile/internal/walk.walkAssignList(0xc0000cfa70, 0xc0003ce720)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/assign.go:146 +0x12f
cmd/compile/internal/walk.walkExpr1({0xe81360, 0xc0003ce720}, 0xc0003ce720?)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/expr.go:183 +0x325
cmd/compile/internal/walk.walkExpr({0xe81360, 0xc0003ce720}, 0xc0000cfa70)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/expr.go:55 +0x428
cmd/compile/internal/walk.walkStmt({0xe81360, 0xc0003ce720?})
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/stmt.go:57 +0x7da
cmd/compile/internal/walk.walkStmtList(...)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/stmt.go:175
cmd/compile/internal/walk.Walk(0xc0003c91e0)
	/home/inso/sdk/gotip/src/cmd/compile/internal/walk/walk.go:43 +0x151
cmd/compile/internal/gc.prepareFunc(0xc0003c91e0)
	/home/inso/sdk/gotip/src/cmd/compile/internal/gc/compile.go:92 +0x6d
cmd/compile/internal/gc.enqueueFunc(0xc0003c91e0)
	/home/inso/sdk/gotip/src/cmd/compile/internal/gc/compile.go:66 +0x2fd
cmd/compile/internal/gc.Main(0xd3da98)
	/home/inso/sdk/gotip/src/cmd/compile/internal/gc/main.go:309 +0xf97
main.main()
	/home/inso/sdk/gotip/src/cmd/compile/main.go:55 +0xdd

[cuonglm]

Sounds like the problem dues to inlining. We implicitly generate OCONVIFACE from .shape.string_0 to interface{}.

cc @randall77 @danscales

[danscales]

Yes, this one is tricky. Easier to discuss if we use this example with no anonymous func and better names:

package main

func genfunc[T any](f func(c T)) {
	var r T

	f(r)
}

func myfunc(c string) {
	test2(c)
}

//go:noinline
func test2(a interface{}) {
}

func main() {
	genfunc(myfunc)
}

I guess this points out a general problem that we may reveal new CONVIFACE calls related to typeparams in a function instantiation after the fact by doing inlining. However, this can only happen if we actually pass in an inlineable function as an argument ("myfunc" here) that matches a relevant typeparam, and then can inline that function call, because we were actually able to inline the function instantiation as well.... (i.e. we were able to inline "genfunc[%2eshape.string_0]" into main, which means we are then able to inline "myfunc" as well.

Because r is "stuck" as a shape type, we need a dictionary when converting r to an empty interface in order to call test2.

We don't want to disable inlining generally in function instantiations, but maybe we can disable inlining for functions that have shape args? Still thinking about it.

[cuonglm]

We do have the .dict param as first argument of genfunc when doing inline. Can we use that?

[danscales]

Sorry, I was a little unclear. As it stands, we want to set the dictionary format for an instantiation (what derived types are relevant, what itabs are needed) right after the stenciling . But in this case, we won't necessarily have the right dictionary entry after the inlining has happened and reveals a new interface conversion (and we would need to run the dictPass again to use that dictionary entry).

[gopherbot]

Change https://golang.org/cl/361260 mentions this issue: cmd/compile: don't inline fn with no shape params, but passed a shape arg

[gopherbot]

Change https://go.dev/cl/424775 mentions this issue: cmd/compile: enable more inlining for unified IR