cmd/link: eliminate a couple of unused DWARF attrs

The linker's DWARF generation occasionally computes and attaches an
attribute X to a type even though the type's abbrev doesn't have the
specified attr. For example, the DW_TAG_subroutine_type abbrev entry
has no type attribute, but a type attr is given to it (wasting
memory). Similarly there are some places where a byte size attr is
added to a DIE whose abbrev lacks that attr. This patch trims away a
few of these not-needed attrs, saving some very tiny amount of memory.

Updates #26186

Change-Id: I69e853df468ac54b07772a614b4106d7c4dae01d
Reviewed-on: https://go-review.googlesource.com/123296
Reviewed-by: Heschi Kreinick <[email protected]>
Run-TryBot: Heschi Kreinick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: thanm

src/cmd/link/internal/ld/dwarf.go

@@ -451,7 +451,6 @@ func newtype(ctxt *Link, gotype *sym.Symbol) *dwarf.DWDie {
 
 	case objabi.KindChan:
 		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_CHANTYPE, name, 0)
-		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
 		s := decodetypeChanElem(ctxt.Arch, gotype)
 		newrefattr(die, dwarf.DW_AT_go_elem, defgotype(ctxt, s))
 		// Save elem type for synthesizechantypes. We could synthesize here
@@ -462,7 +461,6 @@ func newtype(ctxt *Link, gotype *sym.Symbol) *dwarf.DWDie {
 		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_FUNCTYPE, name, 0)
 		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
 		dotypedef(ctxt, &dwtypes, name, die)
-		newrefattr(die, dwarf.DW_AT_type, mustFind(ctxt, "void"))
 		nfields := decodetypeFuncInCount(ctxt.Arch, gotype)
 		for i := 0; i < nfields; i++ {
 			s := decodetypeFuncInType(ctxt.Arch, gotype, i)
@@ -483,7 +481,6 @@ func newtype(ctxt *Link, gotype *sym.Symbol) *dwarf.DWDie {
 	case objabi.KindInterface:
 		die = newdie(ctxt, &dwtypes, dwarf.DW_ABRV_IFACETYPE, name, 0)
 		dotypedef(ctxt, &dwtypes, name, die)
-		newattr(die, dwarf.DW_AT_byte_size, dwarf.DW_CLS_CONSTANT, bytesize, 0)
 		nfields := int(decodetypeIfaceMethodCount(ctxt.Arch, gotype))
 		var s *sym.Symbol
 		if nfields == 0 {