cmd/compile: deal with constructed types that have shapes in them

We convert type args to shape types inside instantiations. If an
instantiation constructs a compound type based on that shape type and
uses that as a type arg to another generic function being called, then
we have a type arg with a shape type embedded inside of it. In that
case, we need to substitute out those embedded shape types with their
underlying type.

If we don't do this, we may create extra unneeded shape types that
have these other shape types embedded in them. This may lead to
generating extra shape instantiations, and a mismatch between the
instantiations that we used in generating dictionaries and the
instantations that are actually called.

Updates #51303

Change-Id: Ieef894a5fac176cfd1415f95926086277ad09759
Reviewed-on: https://go-review.googlesource.com/c/go/+/387674
Reviewed-by: Keith Randall <[email protected]>
Trust: Dan Scales <[email protected]>
Run-TryBot: Dan Scales <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: danscales

src/cmd/compile/internal/typecheck/subr.go

@@ -1424,6 +1424,68 @@ func genericTypeName(sym *types.Sym) string {
 	return sym.Name[0:strings.Index(sym.Name, "[")]
 }
 
+// getShapes appends the list of the shape types that are used within type t to
+// listp. The type traversal is simplified for two reasons: (1) we can always stop a
+// type traversal when t.HasShape() is false; and (2) shape types can't appear inside
+// a named type, except for the type args of a generic type. So, the traversal will
+// always stop before we have to deal with recursive types.
+func getShapes(t *types.Type, listp *[]*types.Type) {
+	if !t.HasShape() {
+		return
+	}
+	if t.IsShape() {
+		*listp = append(*listp, t)
+		return
+	}
+
+	if t.Sym() != nil {
+		// A named type can't have shapes in it, except for type args of a
+		// generic type. We will have to deal with this differently once we
+		// alloc local types in generic functions (#47631).
+		for _, rparam := range t.RParams() {
+			getShapes(rparam, listp)
+		}
+		return
+	}
+
+	switch t.Kind() {
+	case types.TARRAY, types.TPTR, types.TSLICE, types.TCHAN:
+		getShapes(t.Elem(), listp)
+
+	case types.TSTRUCT:
+		for _, f := range t.FieldSlice() {
+			getShapes(f.Type, listp)
+		}
+
+	case types.TFUNC:
+		for _, f := range t.Recvs().FieldSlice() {
+			getShapes(f.Type, listp)
+		}
+		for _, f := range t.Params().FieldSlice() {
+			getShapes(f.Type, listp)
+		}
+		for _, f := range t.Results().FieldSlice() {
+			getShapes(f.Type, listp)
+		}
+		for _, f := range t.TParams().FieldSlice() {
+			getShapes(f.Type, listp)
+		}
+
+	case types.TINTER:
+		for _, f := range t.Methods().Slice() {
+			getShapes(f.Type, listp)
+		}
+
+	case types.TMAP:
+		getShapes(t.Key(), listp)
+		getShapes(t.Elem(), listp)
+
+	default:
+		panic(fmt.Sprintf("Bad type in getShapes: %v", t.Kind()))
+	}
+
+}
+
 // Shapify takes a concrete type and a type param index, and returns a GCshape type that can
 // be used in place of the input type and still generate identical code.
 // No methods are added - all methods calls directly on a shape should
@@ -1442,6 +1504,30 @@ func genericTypeName(sym *types.Sym) string {
 //  instantiation.
 func Shapify(t *types.Type, index int, tparam *types.Type) *types.Type {
 	assert(!t.IsShape())
+	if t.HasShape() {
+		// We are sometimes dealing with types from a shape instantiation
+		// that were constructed from existing shape types, so t may
+		// sometimes have shape types inside it. In that case, we find all
+		// those shape types with getShapes() and replace them with their
+		// underlying type.
+		//
+		// If we don't do this, we may create extra unneeded shape types that
+		// have these other shape types embedded in them. This may lead to
+		// generating extra shape instantiations, and a mismatch between the
+		// instantiations that we used in generating dictionaries and the
+		// instantations that are actually called. (#51303).
+		list := []*types.Type{}
+		getShapes(t, &list)
+		list2 := make([]*types.Type, len(list))
+		for i, shape := range list {
+			list2[i] = shape.Underlying()
+		}
+		ts := Tsubster{
+			Tparams: list,
+			Targs:   list2,
+		}
+		t = ts.Typ(t)
+	}
 	// Map all types with the same underlying type to the same shape.
 	u := t.Underlying()
 

test/typeparam/issue51303.go

@@ -0,0 +1,65 @@
+// run -gcflags=-G=3
+
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"fmt"
+)
+
+func main() {
+	x := [][]int{{1}}
+	y := [][]int{{2, 3}}
+	IntersectSS(x, y)
+}
+
+type list[E any] interface {
+	~[]E
+	Equal(x, y E) bool
+}
+
+// ss is a set of sets
+type ss[E comparable, T []E] []T
+
+func (ss[E, T]) Equal(a, b T) bool {
+	return SetEq(a, b)
+}
+
+func IntersectSS[E comparable](x, y [][]E) [][]E {
+	return IntersectT[[]E, ss[E, []E]](ss[E, []E](x), ss[E, []E](y))
+}
+
+func IntersectT[E any, L list[E]](x, y L) L {
+	var z L
+outer:
+	for _, xe := range x {
+		fmt.Println("xe", xe)
+		for _, ye := range y {
+			fmt.Println("ye", ye)
+			fmt.Println("x", x)
+			if x.Equal(xe, ye) {
+				fmt.Println("appending")
+				z = append(z, xe)
+				continue outer
+			}
+		}
+	}
+	return z
+}
+
+func SetEq[S []E, E comparable](x, y S) bool {
+	fmt.Println("SetEq", x, y)
+outer:
+	for _, xe := range x {
+		for _, ye := range y {
+			if xe == ye {
+				continue outer
+			}
+		}
+		return false // xs wasn't found in y
+	}
+	return true
+}

test/typeparam/issue51303.out

@@ -0,0 +1,4 @@
+xe [1]
+ye [2 3]
+x [[1]]
+SetEq [1] [2 3]