diff --git a/src/cmd/compile/internal/types2/call.go b/src/cmd/compile/internal/types2/call.go
index 23738e2aac..54f6c7ee48 100644
--- a/src/cmd/compile/internal/types2/call.go
+++ b/src/cmd/compile/internal/types2/call.go
@@ -14,13 +14,26 @@ import (
 	"unicode"
 )
 
-// funcInst type-checks a function instantiation and returns the result in x.
-// The incoming x must be an uninstantiated generic function. If inst != nil,
-// it provides (some or all of) the type arguments (inst.Index) for the
-// instantiation. If the target type tsig != nil, the signature's parameter
-// types are used to infer additional missing type arguments of x, if any.
-// At least one of tsig or inst must be provided.
-func (check *Checker) funcInst(tsig *Signature, pos syntax.Pos, x *operand, inst *syntax.IndexExpr) {
+// funcInst type-checks a function instantiation.
+// The incoming x must be a generic function.
+// If inst != nil, it provides some or all of the type arguments (inst.Index).
+// If target type tsig != nil, the signature may be used to infer missing type
+// arguments of x, if any. At least one of tsig or inst must be provided.
+//
+// There are two modes of operation:
+//
+//  1. If infer == true, funcInst infers missing type arguments as needed and
+//     instantiates the function x. The returned results are nil.
+//
+//  2. If infer == false and inst provides all type arguments, funcInst
+//     instantiates the function x. The returned results are nil.
+//     If inst doesn't provide enough type arguments, funcInst returns the
+//     available arguments and the corresponding expression list; x remains
+//     unchanged.
+//
+// If an error (other than a version error) occurs in any case, it is reported
+// and x.mode is set to invalid.
+func (check *Checker) funcInst(tsig *Signature, pos syntax.Pos, x *operand, inst *syntax.IndexExpr, infer bool) ([]Type, []syntax.Expr) {
 	assert(tsig != nil || inst != nil)
 
 	var instErrPos poser
@@ -40,7 +53,7 @@ func (check *Checker) funcInst(tsig *Signature, pos syntax.Pos, x *operand, inst
 		if targs == nil {
 			x.mode = invalid
 			x.expr = inst
-			return
+			return nil, nil
 		}
 		assert(len(targs) == len(xlist))
 	}
@@ -55,10 +68,14 @@ func (check *Checker) funcInst(tsig *Signature, pos syntax.Pos, x *operand, inst
 		check.errorf(xlist[got-1], WrongTypeArgCount, "got %d type arguments but want %d", got, want)
 		x.mode = invalid
 		x.expr = inst
-		return
+		return nil, nil
 	}
 
 	if got < want {
+		if !infer {
+			return targs, xlist
+		}
+
 		// If the uninstantiated or partially instantiated function x is used in an
 		// assignment (tsig != nil), use the respective function parameter and result
 		// types to infer additional type arguments.
@@ -104,7 +121,7 @@ func (check *Checker) funcInst(tsig *Signature, pos syntax.Pos, x *operand, inst
 			// error was already reported
 			x.mode = invalid
 			x.expr = inst
-			return
+			return nil, nil
 		}
 		got = len(targs)
 	}
@@ -121,6 +138,7 @@ func (check *Checker) funcInst(tsig *Signature, pos syntax.Pos, x *operand, inst
 		x.expr = inst
 	}
 	check.recordInstance(x.expr, targs, sig)
+	return nil, nil
 }
 
 func paramName(name string, i int, kind string) string {
diff --git a/src/cmd/compile/internal/types2/expr.go b/src/cmd/compile/internal/types2/expr.go
index 0f473293bc..e69f2e4c10 100644
--- a/src/cmd/compile/internal/types2/expr.go
+++ b/src/cmd/compile/internal/types2/expr.go
@@ -995,7 +995,7 @@ func (check *Checker) nonGeneric(T Type, x *operand) {
 		if t.tparams != nil {
 			if enableReverseTypeInference && T != nil {
 				if tsig, _ := under(T).(*Signature); tsig != nil {
-					check.funcInst(tsig, x.Pos(), x, nil)
+					check.funcInst(tsig, x.Pos(), x, nil, true)
 					return
 				}
 			}
@@ -1322,7 +1322,7 @@ func (check *Checker) exprInternal(T Type, x *operand, e syntax.Expr, hint Type)
 			if enableReverseTypeInference && T != nil {
 				tsig, _ = under(T).(*Signature)
 			}
-			check.funcInst(tsig, e.Pos(), x, e)
+			check.funcInst(tsig, e.Pos(), x, e, true)
 		}
 		if x.mode == invalid {
 			goto Error
diff --git a/src/go/types/call.go b/src/go/types/call.go
index f2ff4cf857..5877a345df 100644
--- a/src/go/types/call.go
+++ b/src/go/types/call.go
@@ -16,13 +16,26 @@ import (
 	"unicode"
 )
 
-// funcInst type-checks a function instantiation and returns the result in x.
-// The incoming x must be an uninstantiated generic function. If ix != nil,
-// it provides (some or all of) the type arguments (ix.Indices) for the
-// instantiation. If the target type tsig != nil, the signature's parameter
-// types are used to infer additional missing type arguments of x, if any.
-// At least one of tsig or ix must be provided.
-func (check *Checker) funcInst(tsig *Signature, pos token.Pos, x *operand, ix *typeparams.IndexExpr) {
+// funcInst type-checks a function instantiation.
+// The incoming x must be a generic function.
+// If ix != nil, it provides some or all of the type arguments (ix.Indices).
+// If target type tsig != nil, the signature may be used to infer missing type
+// arguments of x, if any. At least one of tsig or inst must be provided.
+//
+// There are two modes of operation:
+//
+//  1. If infer == true, funcInst infers missing type arguments as needed and
+//     instantiates the function x. The returned results are nil.
+//
+//  2. If infer == false and inst provides all type arguments, funcInst
+//     instantiates the function x. The returned results are nil.
+//     If inst doesn't provide enough type arguments, funcInst returns the
+//     available arguments and the corresponding expression list; x remains
+//     unchanged.
+//
+// If an error (other than a version error) occurs in any case, it is reported
+// and x.mode is set to invalid.
+func (check *Checker) funcInst(tsig *Signature, pos token.Pos, x *operand, ix *typeparams.IndexExpr, infer bool) ([]Type, []ast.Expr) {
 	assert(tsig != nil || ix != nil)
 
 	var instErrPos positioner
@@ -42,7 +55,7 @@ func (check *Checker) funcInst(tsig *Signature, pos token.Pos, x *operand, ix *t
 		if targs == nil {
 			x.mode = invalid
 			x.expr = ix
-			return
+			return nil, nil
 		}
 		assert(len(targs) == len(xlist))
 	}
@@ -57,10 +70,14 @@ func (check *Checker) funcInst(tsig *Signature, pos token.Pos, x *operand, ix *t
 		check.errorf(ix.Indices[got-1], WrongTypeArgCount, "got %d type arguments but want %d", got, want)
 		x.mode = invalid
 		x.expr = ix.Orig
-		return
+		return nil, nil
 	}
 
 	if got < want {
+		if !infer {
+			return targs, xlist
+		}
+
 		// If the uninstantiated or partially instantiated function x is used in an
 		// assignment (tsig != nil), use the respective function parameter and result
 		// types to infer additional type arguments.
@@ -108,7 +125,7 @@ func (check *Checker) funcInst(tsig *Signature, pos token.Pos, x *operand, ix *t
 			// error was already reported
 			x.mode = invalid
 			x.expr = ix // TODO(gri) is this correct?
-			return
+			return nil, nil
 		}
 		got = len(targs)
 	}
@@ -125,6 +142,7 @@ func (check *Checker) funcInst(tsig *Signature, pos token.Pos, x *operand, ix *t
 		x.expr = ix.Orig
 	}
 	check.recordInstance(x.expr, targs, sig)
+	return nil, nil
 }
 
 func paramName(name string, i int, kind string) string {
diff --git a/src/go/types/expr.go b/src/go/types/expr.go
index b0e1422b01..898c562785 100644
--- a/src/go/types/expr.go
+++ b/src/go/types/expr.go
@@ -980,7 +980,7 @@ func (check *Checker) nonGeneric(T Type, x *operand) {
 		if t.tparams != nil {
 			if enableReverseTypeInference && T != nil {
 				if tsig, _ := under(T).(*Signature); tsig != nil {
-					check.funcInst(tsig, x.Pos(), x, nil)
+					check.funcInst(tsig, x.Pos(), x, nil, true)
 					return
 				}
 			}
@@ -1305,7 +1305,7 @@ func (check *Checker) exprInternal(T Type, x *operand, e ast.Expr, hint Type) ex
 			if enableReverseTypeInference && T != nil {
 				tsig, _ = under(T).(*Signature)
 			}
-			check.funcInst(tsig, e.Pos(), x, ix)
+			check.funcInst(tsig, e.Pos(), x, ix, true)
 		}
 		if x.mode == invalid {
 			goto Error