[dev.cmdgo] all: merge master (5e6a7e9) into dev.cmdgo

Merge List:

+ 2021-08-26 5e6a7e9b86 embed: remove reference to global variables in docs
+ 2021-08-26 166b691b65 cmd/compile/internal/types2: remove need for instance (struct)
+ 2021-08-26 d6bdae33e9 cmd/compile/internal/types2: address some TODOs (cleanup)
+ 2021-08-26 770df2e18d crypto/tls: fix typo in PreferServerCipherSuites comment
+ 2021-08-26 a6ff433d6a cmd/go: pass -gcflags after other flags generated by the go command
+ 2021-08-25 4f2620285d cmd/compile/internal/types2: fix type set printing and add test
+ 2021-08-25 0ac64f6d70 cmd/compile/internal/types2: rename IsMethodSet to IsConstraint (cleanup)
+ 2021-08-25 4068fb6c21 cmd/compile: always accept 1.18 syntax but complain if not 1.18
+ 2021-08-25 bf0bc4122f go/types, types2: don't re-evaluate context string for each function argument (optimization)
+ 2021-08-25 4158e88f64 cmd/compile/internal/syntax: fix position of type parameter field
+ 2021-08-25 647bef6c59 go/types: implement NewTypeList and use it instead of composite literals
+ 2021-08-25 6cf1d5d0fa cmd/compile: generic SSA rules for simplifying 2 and 3 operand integer arithmetic expressions
+ 2021-08-25 5baf60d472 bytes, strings: optimize Trim for single byte cutsets
+ 2021-08-25 3d667671ad cmd/compile: fix function contains no TParam in generic function
+ 2021-08-25 4f2ebfe34b cmd/compile: allow embed into any byte slice type
+ 2021-08-25 d2f002cb39 time/format: avoid growslice in time.String()/time.GoString()
+ 2021-08-25 08d4cc20ca cmd/compile: fix stencil call expression.
+ 2021-08-25 099b819085 cmd/compile: fix CheckSize() calculation for -G=3 and stencils
+ 2021-08-25 e1fcf8857e test: add test that caused gofrontend compiler crash
+ 2021-08-25 d37b8dedf7 test: add test case that gofrontend miscompiled
+ 2021-08-25 41b99dab0f os/user: don't skip TestLookupGroup if supported
+ 2021-08-25 de1c934b97 cmd/compile: fix checkptr false positive for (*[Big]T)(ptr)[:n:n] pattern
+ 2021-08-24 54cdef1f10 reflect: add MapIter.SetKey and MapIter.SetValue
+ 2021-08-24 5d863f89fe cmd/compile: simplify bad conversion check

Change-Id: I29ab927f0e47f44d82f9307c642900f75f4f678f

1 files changed, 21 insertions, 30 deletions

diff --git a/src/cmd/compile/internal/types2/instantiate.go b/src/cmd/compile/internal/types2/instantiate.go
index 8bea63ec86..f9cde24dfc 100644
--- a/src/cmd/compile/internal/types2/instantiate.go
+++ b/src/cmd/compile/internal/types2/instantiate.go
@@ -122,27 +122,26 @@ func (check *Checker) instantiate(pos syntax.Pos, typ Type, targs []Type, posLis
 // instance creates a type or function instance using the given original type
 // typ and arguments targs. For Named types the resulting instance will be
 // unexpanded.
-func (check *Checker) instance(pos syntax.Pos, typ Type, targs []Type) (res Type) {
-	// TODO(gri) What is better here: work with TypeParams, or work with TypeNames?
+func (check *Checker) instance(pos syntax.Pos, typ Type, targs []Type) Type {
 	switch t := typ.(type) {
 	case *Named:
 		h := instantiatedHash(t, targs)
 		if check != nil {
-			// typ may already have been instantiated with identical type arguments. In
-			// that case, re-use the existing instance.
+			// typ may already have been instantiated with identical type arguments.
+			// In that case, re-use the existing instance.
 			if named := check.typMap[h]; named != nil {
 				return named
 			}
 		}
-
 		tname := NewTypeName(pos, t.obj.pkg, t.obj.name, nil)
 		named := check.newNamed(tname, t, nil, nil, nil) // methods and tparams are set when named is loaded
 		named.targs = NewTypeList(targs)
-		named.instance = &instance{pos}
+		named.instPos = &pos
 		if check != nil {
 			check.typMap[h] = named
 		}
-		res = named
+		return named
+
 	case *Signature:
 		tparams := t.TParams()
 		if !check.validateTArgLen(pos, tparams.Len(), len(targs)) {
@@ -151,30 +150,22 @@ func (check *Checker) instance(pos syntax.Pos, typ Type, targs []Type) (res Type
 		if tparams.Len() == 0 {
 			return typ // nothing to do (minor optimization)
 		}
-		defer func() {
-			// If we had an unexpected failure somewhere don't panic below when
-			// asserting res.(*Signature). Check for *Signature in case Typ[Invalid]
-			// is returned.
-			if _, ok := res.(*Signature); !ok {
-				return
-			}
-			// If the signature doesn't use its type parameters, subst
-			// will not make a copy. In that case, make a copy now (so
-			// we can set tparams to nil w/o causing side-effects).
-			if t == res {
-				copy := *t
-				res = &copy
-			}
-			// After instantiating a generic signature, it is not generic
-			// anymore; we need to set tparams to nil.
-			res.(*Signature).tparams = nil
-		}()
-		res = check.subst(pos, typ, makeSubstMap(tparams.list(), targs), nil)
-	default:
-		// only types and functions can be generic
-		panic(fmt.Sprintf("%v: cannot instantiate %v", pos, typ))
+		sig := check.subst(pos, typ, makeSubstMap(tparams.list(), targs), nil).(*Signature)
+		// If the signature doesn't use its type parameters, subst
+		// will not make a copy. In that case, make a copy now (so
+		// we can set tparams to nil w/o causing side-effects).
+		if sig == t {
+			copy := *sig
+			sig = &copy
+		}
+		// After instantiating a generic signature, it is not generic
+		// anymore; we need to set tparams to nil.
+		sig.tparams = nil
+		return sig
 	}
-	return res
+
+	// only types and functions can be generic
+	panic(fmt.Sprintf("%v: cannot instantiate %v", pos, typ))
 }
 
 // validateTArgLen verifies that the length of targs and tparams matches,