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runtime: clarify that itab.hash of dynamic entries is unused

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The hash is used in type switches. However, compiler statically generates itab's
for all interface/type pairs used in switches (which are added to itabTable
in itabsinit). The dynamically-generated itab's never participate in type switches,
and thus the hash is irrelevant.

Change-Id: I4f6e37be31b8f5605cca7a1806cb04708e948cea
Reviewed-on: https://go-review.googlesource.com/c/go/+/202448
Run-TryBot: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Dmitry Vyukov 2019-10-22 14:20:51 +02:00
parent f71bd516b7
commit 61089984a8
1 changed files with 6 additions and 1 deletions
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7
src/runtime/iface.go
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@ -66,6 +66,12 @@ func getitab(inter *interfacetype, typ *_type, canfail bool) *itab {
m = (*itab)(persistentalloc(unsafe.Sizeof(itab{})+uintptr(len(inter.mhdr)-1)*sys.PtrSize, 0, &memstats.other_sys))
m.inter = inter
m._type = typ
// The hash is used in type switches. However, compiler statically generates itab's
// for all interface/type pairs used in switches (which are added to itabTable
// in itabsinit). The dynamically-generated itab's never participate in type switches,
// and thus the hash is irrelevant.
// Note: m.hash is _not_ the hash used for the runtime itabTable hash table.
m.hash = 0
m.init()
itabAdd(m)
unlock(&itabLock)
@ -233,7 +239,6 @@ imethods:
return iname
}
m.fun[0] = uintptr(fun0)
m.hash = typ.hash
return ""
}