cmd/compile: getting more built-ins to work with generics

For Builtin ops, we currently stay with using the old
typechecker to transform the call to a more specific expression
and possibly use more specific ops. However, for a bunch of the
ops, we delay calling the old typechecker if any of the args have
type params, for a variety of reasons.

In the near future, we will start creating separate functions that do
the same transformations as the old typechecker for calls, builtins,
indexing, comparisons, etc. These functions can then be called at noder
time for nodes with no type params, and at stenciling time for nodes
with type params.

Remove unnecessary calls to types1 typechecker for most kinds of
statements (still need it for SendStmt, AssignStmt, ReturnStmt, and
SelectStmt). In particular, we don't need it for RangeStmt, and this
avoids some complaints by the types1 typechecker on generic code.

Other small changes:
 - Fix check on whether to delay calling types1-typechecker on type
   conversions. Should check if HasTParam is true, rather than if the
   type is directly a TYPEPARAM.

 - Don't call types1-typechecker on an indexing operation if the left
   operand has a typeparam in its type and is not obviously a TMAP,
   TSLICE, or TARRAY. As above, we will eventually have to create a new
   function that can do the required transformations (for complicated
   cases) at noder time or stenciling time.

 - Copy n.BuiltinOp in subster.node()

 - The complex arithmetic example in absdiff.go now works.

 - Added new tests double.go and append.go

 - Added new example with a new() call in settable.go

Change-Id: I8f377afb6126cab1826bd3c2732aa8cdf1f7e0b4
Reviewed-on: https://go-review.googlesource.com/c/go/+/301951
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Dan Scales <danscales@google.com>
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

1 files changed, 17 insertions, 18 deletions

diff --git a/test/typeparam/absdiff.go b/test/typeparam/absdiff.go
index 5dd58f14f7..1381d7c92c 100644
--- a/test/typeparam/absdiff.go
+++ b/test/typeparam/absdiff.go
@@ -8,7 +8,7 @@ package main
 
 import (
 	"fmt"
-	//"math"
+	"math"
 )
 
 type Numeric interface {
@@ -57,14 +57,14 @@ func (a orderedAbs[T]) Abs() orderedAbs[T] {
 
 // complexAbs is a helper type that defines an Abs method for
 // complex types.
-// type complexAbs[T Complex] T
+type complexAbs[T Complex] T
 
-// func (a complexAbs[T]) Abs() complexAbs[T] {
-// 	r := float64(real(a))
-// 	i := float64(imag(a))
-// 	d := math.Sqrt(r * r + i * i)
-// 	return complexAbs[T](complex(d, 0))
-// }
+func (a complexAbs[T]) Abs() complexAbs[T] {
+	r := float64(real(a))
+	i := float64(imag(a))
+	d := math.Sqrt(r * r + i * i)
+	return complexAbs[T](complex(d, 0))
+}
 
 // OrderedAbsDifference returns the absolute value of the difference
 // between a and b, where a and b are of an ordered type.
@@ -74,9 +74,9 @@ func orderedAbsDifference[T orderedNumeric](a, b T) T {
 
 // ComplexAbsDifference returns the absolute value of the difference
 // between a and b, where a and b are of a complex type.
-// func complexAbsDifference[T Complex](a, b T) T {
-// 	return T(absDifference(complexAbs[T](a), complexAbs[T](b)))
-// }
+func complexAbsDifference[T Complex](a, b T) T {
+	return T(absDifference(complexAbs[T](a), complexAbs[T](b)))
+}
 
 func main() {
 	if got, want := orderedAbsDifference(1.0, -2.0), 3.0; got != want {
@@ -89,11 +89,10 @@ func main() {
 		panic(fmt.Sprintf("got = %v, want = %v", got, want))
 	}
 
-	// Still have to handle built-ins real/abs to make this work
-	// if got, want := complexAbsDifference(5.0 + 2.0i, 2.0 - 2.0i), 5; got != want {
-	//	panic(fmt.Sprintf("got = %v, want = %v", got, want)
-	// }
-	// if got, want := complexAbsDifference(2.0 - 2.0i, 5.0 + 2.0i), 5; got != want {
-	//	panic(fmt.Sprintf("got = %v, want = %v", got, want)
-	// }
+	if got, want := complexAbsDifference(5.0 + 2.0i, 2.0 - 2.0i), 5+0i; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
+	if got, want := complexAbsDifference(2.0 - 2.0i, 5.0 + 2.0i), 5+0i; got != want {
+		panic(fmt.Sprintf("got = %v, want = %v", got, want))
+	}
 }