cmd/compile: add types.RecalcSize

This is the only case where Align is assigned outside of package
types. Rather than adding a SetAlign method, adding a RecalcSize
function is a bit more descriptive.

Change-Id: I1b3c01ebd0e41183665baa63c926592865bbbd0b
Reviewed-on: https://go-review.googlesource.com/c/go/+/345479
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

src/cmd/compile/internal/noder/func.go

@@ -37,8 +37,7 @@ func (g *irgen) funcBody(fn *ir.Func, recv *syntax.Field, sig *syntax.FuncType,
 	// calculated its size, including parameter offsets. Now that we've
 	// created the parameter Names, force a recalculation to ensure
 	// their offsets are correct.
-	typ.Align = 0
-	types.CalcSize(typ)
+	types.RecalcSize(typ)
 
 	if block != nil {
 		typecheck.DeclContext = ir.PAUTO

src/cmd/compile/internal/types/size.go

@@ -562,6 +562,14 @@ func CalcStructSize(s *Type) {
 	s.Width = calcStructOffset(s, s, 0, 1) // sets align
 }
 
+// RecalcSize is like CalcSize, but recalculates t's size even if it
+// has already been calculated before. It does not recalculate other
+// types.
+func RecalcSize(t *Type) {
+	t.Align = 0
+	CalcSize(t)
+}
+
 // when a type's width should be known, we call CheckSize
 // to compute it.  during a declaration like
 //