cmd/compile/internal/syntax: add Unparen and UnpackListExpr helpers

We've added Unparen to go/ast, so add syntax.Unparen to be
consistent (and because it's similarly useful).

Also, types2 and noder both have similar functions for unpacking
ListExprs, so might as well add a common implementation in package
syntax too.

Finally, addressing the TODO: UnpackListExpr is small enough to be
inlined (when default optimizations are enabled), and for typical uses
of UnpackListExpr (e.g., "range UnpackListExpr(x)") the single-element
slice result is stack allocated in the caller. This CL adds a test
using testing.AllocsPerRun to ensure this remains so in the future.

Change-Id: I96a5591d202193ed5bf1ce6f290919107e3dc01b
Reviewed-on: https://go-review.googlesource.com/c/go/+/522336
Auto-Submit: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>

1 files changed, 0 insertions, 21 deletions

diff --git a/src/cmd/compile/internal/noder/expr.go b/src/cmd/compile/internal/noder/expr.go
index 51b0656385..14ef3b958f 100644
--- a/src/cmd/compile/internal/noder/expr.go
+++ b/src/cmd/compile/internal/noder/expr.go
@@ -11,17 +11,6 @@ import (
 	"cmd/compile/internal/syntax"
 )
 
-func unpackListExpr(expr syntax.Expr) []syntax.Expr {
-	switch expr := expr.(type) {
-	case nil:
-		return nil
-	case *syntax.ListExpr:
-		return expr.ElemList
-	default:
-		return []syntax.Expr{expr}
-	}
-}
-
 // constExprOp returns an ir.Op that represents the outermost
 // operation of the given constant expression. It's intended for use
 // with ir.RawOrigExpr.
@@ -43,13 +32,3 @@ func constExprOp(expr syntax.Expr) ir.Op {
 		return binOps[expr.Op]
 	}
 }
-
-func unparen(expr syntax.Expr) syntax.Expr {
-	for {
-		paren, ok := expr.(*syntax.ParenExpr)
-		if !ok {
-			return expr
-		}
-		expr = paren.X
-	}
-}