[dev.typeparams] cmd/compile: remove some shape checks in type substituter, other cleanups

The type substituter (typecheck.Typ()) was temporarily substituting from
shapes back to concrete types, but doesn't need to anymore. So, remove
two shape checks, so the type substituter is now only for substituting
type params again.

Several other cleanups:

 - renamed makeGenericName() to makeInstName1(), since that function is
   a helper to MakeInstName() and MakeDictName() that definitely makes
   instantiated names, not generic names.

 - removed the logic in makeInstName1() that adds the ".inst." prefix
   for concrete type args. We are only specifying concrete type args (as
   opposed to shape args) when we are calling from MakeDictName, and
   then we immediately strip of the .inst prefix anyway.

 - Added a comment on types.Identical that a shape type is considered
   identicall to another type if their underlying types are the same, or
   they are both pointers.

Change-Id: I3e0206dbd403897797ae7bec3c527ae16b0b930a
Reviewed-on: https://go-review.googlesource.com/c/go/+/341729
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>

2 files changed, 15 insertions, 32 deletions

diff --git a/src/cmd/compile/internal/typecheck/subr.go b/src/cmd/compile/internal/typecheck/subr.go
index e86c4c6bca..c7a3718b31 100644
--- a/src/cmd/compile/internal/typecheck/subr.go
+++ b/src/cmd/compile/internal/typecheck/subr.go
@@ -900,31 +900,11 @@ func TypesOf(x []ir.Node) []*types.Type {
 	return r
 }
 
-// makeGenericName returns the name of the generic function instantiated
-// with the given types.
-// name is the name of the generic function or method.
-func makeGenericName(name string, targs []*types.Type, hasBrackets bool) string {
+// makeInstName1 returns the name of the generic function instantiated with the
+// given types, which can have type params or shapes, or be concrete types. name is
+// the name of the generic function or method.
+func makeInstName1(name string, targs []*types.Type, hasBrackets bool) string {
 	b := bytes.NewBufferString("")
-
-	// Determine if the type args are concrete types or new typeparams.
-	hasTParam := false
-	for _, targ := range targs {
-		if hasTParam {
-			assert(targ.HasTParam() || targ.HasShape())
-		} else if targ.HasTParam() || targ.HasShape() {
-			hasTParam = true
-		}
-	}
-
-	// Marker to distinguish generic instantiations from fully stenciled wrapper functions.
-	// Once we move to GC shape implementations, this prefix will not be necessary as the
-	// GC shape naming will distinguish them.
-	// e.g. f[8bytenonpointer] vs. f[int].
-	// For now, we use .inst.f[int] vs. f[int].
-	if !hasTParam {
-		b.WriteString(".inst.")
-	}
-
 	i := strings.Index(name, "[")
 	assert(hasBrackets == (i >= 0))
 	if i >= 0 {
@@ -963,7 +943,7 @@ func makeGenericName(name string, targs []*types.Type, hasBrackets bool) string
 
 // MakeInstName makes the unique name for a stenciled generic function or method,
 // based on the name of the function fnsym and the targs. It replaces any
-// existing bracket type list in the name. makeInstName asserts that fnsym has
+// existing bracket type list in the name. MakeInstName asserts that fnsym has
 // brackets in its name if and only if hasBrackets is true.
 //
 // Names of declared generic functions have no brackets originally, so hasBrackets
@@ -974,7 +954,7 @@ func makeGenericName(name string, targs []*types.Type, hasBrackets bool) string
 // The standard naming is something like: 'genFn[int,bool]' for functions and
 // '(*genType[int,bool]).methodName' for methods
 func MakeInstName(gf *types.Sym, targs []*types.Type, hasBrackets bool) *types.Sym {
-	return gf.Pkg.Lookup(makeGenericName(gf.Name, targs, hasBrackets))
+	return gf.Pkg.Lookup(makeInstName1(gf.Name, targs, hasBrackets))
 }
 
 func MakeDictName(gf *types.Sym, targs []*types.Type, hasBrackets bool) *types.Sym {
@@ -987,8 +967,8 @@ func MakeDictName(gf *types.Sym, targs []*types.Type, hasBrackets bool) *types.S
 			panic("dictionary should always have concrete type args")
 		}
 	}
-	name := makeGenericName(gf.Name, targs, hasBrackets)
-	name = ".dict." + name[6:]
+	name := makeInstName1(gf.Name, targs, hasBrackets)
+	name = ".dict." + name
 	return gf.Pkg.Lookup(name)
 }
 
@@ -1014,14 +994,14 @@ type Tsubster struct {
 // result is t; otherwise the result is a new type. It deals with recursive types
 // by using TFORW types and finding partially or fully created types via sym.Def.
 func (ts *Tsubster) Typ(t *types.Type) *types.Type {
-	if !t.HasTParam() && !t.HasShape() && t.Kind() != types.TFUNC {
+	if !t.HasTParam() && t.Kind() != types.TFUNC {
 		// Note: function types need to be copied regardless, as the
 		// types of closures may contain declarations that need
 		// to be copied. See #45738.
 		return t
 	}
 
-	if t.IsTypeParam() || t.IsShape() {
+	if t.IsTypeParam() {
 		for i, tp := range ts.Tparams {
 			if tp == t {
 				return ts.Targs[i]
diff --git a/src/cmd/compile/internal/types/identity.go b/src/cmd/compile/internal/types/identity.go
index dc39acced8..2e9e2f4fd8 100644
--- a/src/cmd/compile/internal/types/identity.go
+++ b/src/cmd/compile/internal/types/identity.go
@@ -4,8 +4,11 @@
 
 package types
 
-// Identical reports whether t1 and t2 are identical types, following
-// the spec rules. Receiver parameter types are ignored.
+// Identical reports whether t1 and t2 are identical types, following the spec rules.
+// Receiver parameter types are ignored. Named (defined) types are only equal if they
+// are pointer-equal - i.e. there must be a unique types.Type for each specific named
+// type. Also, a type containing a shape type is considered identical to another type
+// (shape or not) if their underlying types are the same, or they are both pointers.
 func Identical(t1, t2 *Type) bool {
 	return identical(t1, t2, true, nil)
 }