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[dev.typeparams] cmd/compile: make type conversions by type parameters work

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When doing a type conversion using a type param, delay the
transformation to OCONV/OCONVNOP until stenciling, since the nodes
created depend on the actual type.

Re-enable the fact.go test.

Change-Id: I3d5861aab3dd0e781d767f67435afaf951dfe451
Reviewed-on: https://go-review.googlesource.com/c/go/+/290752
Trust: Dan Scales <danscales@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Dan Scales 2021-02-09 15:13:19 -08:00
parent 12e15d430d
commit fdf3496fcc
3 changed files with 33 additions and 27 deletions
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5
src/cmd/compile/internal/noder/helpers.go
View File

@ -84,6 +84,11 @@ func Call(pos src.XPos, typ *types.Type, fun ir.Node, args []ir.Node, dots bool)
if fun.Op() == ir.OTYPE {
// Actually a type conversion, not a function call.
n := ir.NewCallExpr(pos, ir.OCALL, fun, args)
if fun.Type().Kind() == types.TTYPEPARAM {
// For type params, don't typecheck until we actually know
// the type.
return typed(typ, n)
}
return typecheck.Expr(n)
}

40
src/cmd/compile/internal/noder/stencil.go
View File

@ -174,30 +174,36 @@ func (subst *subster) node(n ir.Node) ir.Node {
}
ir.EditChildren(m, edit)
// A method value/call via a type param will have been left as an
// OXDOT. When we see this during stenciling, finish the
// typechecking, now that we have the instantiated receiver type.
// We need to do this now, since the access/selection to the
// method for the real type is very different from the selection
// for the type param.
if x.Op() == ir.OXDOT {
// Will transform to an OCALLPART
// A method value/call via a type param will have been left as an
// OXDOT. When we see this during stenciling, finish the
// typechecking, now that we have the instantiated receiver type.
// We need to do this now, since the access/selection to the
// method for the real type is very different from the selection
// for the type param.
m.SetTypecheck(0)
// m will transform to an OCALLPART
typecheck.Expr(m)
}
if x.Op() == ir.OCALL {
call := m.(*ir.CallExpr)
if call.X.Op() != ir.OCALLPART {
base.FatalfAt(call.Pos(), "Expecting OXDOT with CALL")
if call.X.Op() == ir.OTYPE {
// Do typechecking on a conversion, now that we
// know the type argument.
m.SetTypecheck(0)
m = typecheck.Expr(m)
} else if call.X.Op() == ir.OCALLPART {
// Redo the typechecking, now that we know the method
// value is being called.
call.X.(*ir.SelectorExpr).SetOp(ir.OXDOT)
call.X.SetTypecheck(0)
call.X.SetType(nil)
typecheck.Callee(call.X)
m.SetTypecheck(0)
typecheck.Call(m.(*ir.CallExpr))
} else {
base.FatalfAt(call.Pos(), "Expecting OCALLPART or OTYPE with CALL")
}
// Redo the typechecking, now that we know the method
// value is being called
call.X.(*ir.SelectorExpr).SetOp(ir.OXDOT)
call.X.SetTypecheck(0)
call.X.SetType(nil)
typecheck.Callee(call.X)
m.SetTypecheck(0)
typecheck.Call(m.(*ir.CallExpr))
}
if x.Op() == ir.OCLOSURE {

15
test/typeparam/fact.go
View File

@ -8,20 +8,15 @@ package main
import "fmt"
// TODO Stenciling doesn't do the right thing for T(1) at the moment.
func fact[T interface { type int, int64, float64 }](n T) T {
// TODO remove this return in favor of the correct computation below
return n
// if n == T(1) {
// return T(1)
// }
// return n * fact(n - T(1))
if n == T(1) {
return T(1)
}
return n * fact(n - T(1))
}
func main() {
// TODO change this to 120 once we can compile the function body above
const want = 5 // 120
const want = 120
if got := fact(5); got != want {
panic(fmt.Sprintf("got %d, want %d", got, want))