[dev.typeparams] cmd/compile: use dictionary to convert arguments of ==, != to interfaces

When comparing a value whose type is a type parameter to an interface,
we need to convert that type parameter to an interface using the dictionary
entries.

Change-Id: I409c9e36e376fe4ef8163407d0fd4e84496d5b65
Reviewed-on: https://go-review.googlesource.com/c/go/+/334150
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

diff --git a/src/cmd/compile/internal/noder/stencil.go b/src/cmd/compile/internal/noder/stencil.go
index 1759fbc4cfde92d717c8fbe614e0edc36721cb07..f4935fe22a4f8ebc91828e8100558e4ed33e63e7 100644 (file)
--- a/src/cmd/compile/internal/noder/stencil.go
+++ b/src/cmd/compile/internal/noder/stencil.go
@@ -1242,6 +1242,21 @@ func (subst *subster) node(n ir.Node) ir.Node {
                        if ix := subst.findDictType(t); ix >= 0 {
                                m = subst.convertUsingDictionary(x.Pos(), m.(*ir.ConvExpr).X, m.Type(), t, ix)
                        }
+               case ir.OEQ, ir.ONE:
+                       // Equality between a non-interface and an interface requires the non-interface
+                       // to be promoted to an interface.
+                       x := x.(*ir.BinaryExpr)
+                       m := m.(*ir.BinaryExpr)
+                       if i := x.Y.Type(); i.IsInterface() {
+                               if ix := subst.findDictType(x.X.Type()); ix >= 0 {
+                                       m.X = subst.convertUsingDictionary(m.X.Pos(), m.X, i, x.X.Type(), ix)
+                               }
+                       }
+                       if i := x.X.Type(); i.IsInterface() {
+                               if ix := subst.findDictType(x.Y.Type()); ix >= 0 {
+                                       m.Y = subst.convertUsingDictionary(m.Y.Pos(), m.Y, i, x.X.Type(), ix)
+                               }
+                       }
                }
                return m
        }

diff --git a/test/typeparam/equal.go b/test/typeparam/equal.go
new file mode 100644 (file)
index 0000000..6776b19
--- /dev/null
+++ b/test/typeparam/equal.go
@@ -0,0 +1,71 @@
+// run -gcflags=-G=3
+
+// Copyright 2021 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.
+
+// comparisons of type parameters to interfaces
+
+package main
+
+func f[T comparable](t, u T) bool {
+       // Comparing two type parameters directly.
+       // (Not really testing comparisons to interfaces, but just 'cause we're here.)
+       return t == u
+}
+
+func g[T comparable](t T, i interface{}) bool {
+       // Compare type parameter value to empty interface.
+       return t == i
+}
+
+type I interface {
+       foo()
+}
+
+type C interface {
+       comparable
+       I
+}
+
+func h[T C](t T, i I) bool {
+       // Compare type parameter value to nonempty interface.
+       return t == i
+}
+
+type myint int
+
+func (x myint) foo() {
+}
+
+func k[T comparable](t T, i interface{}) bool {
+       // Compare derived type value to interface.
+       return struct{a, b T}{t, t} == i
+}
+
+func main() {
+       assert(f(3, 3))
+       assert(!f(3, 5))
+       assert(g(3, 3))
+       assert(!g(3, 5))
+       assert(h(myint(3), myint(3)))
+       assert(!h(myint(3), myint(5)))
+
+       type S struct { a, b float64 }
+
+       assert(f(S{3,5}, S{3,5}))
+       assert(!f(S{3,5}, S{4,6}))
+       assert(g(S{3,5}, S{3,5}))
+       assert(!g(S{3,5}, S{4,6}))
+
+       assert(k(3, struct{a, b int}{3, 3}))
+       assert(!k(3, struct{a, b int}{3, 4}))
+}
+
+func assert(b bool)  {
+       if !b {
+               panic("assertion failed")
+       }
+}
+
+