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Re: alpha haifa regression
- To: Jim Wilson <wilson at cygnus dot com>
- Subject: Re: alpha haifa regression
- From: Jeffrey A Law <law at cygnus dot com>
- Date: Mon, 29 Sep 1997 14:32:56 -0600
- cc: rth at cygnus dot com (Richard Henderson), egcs at cygnus dot com
- Reply-To: law at cygnus dot com
In message <199709292023.NAA04543@cygnus.com>you write:
> I think the correct fix here is to set the MEM_IN_STRUCT_P bit on the
> MEM rtx created by SETUP_INCOMING_VARARGS. This should make the sched
> blockage insn unnecessary.
>
> The MEM_IN_STRUCT_P bit should be set because these are not scalar stores.
You're probably right. However the blockage will still be needed.
If you set MEM_IN_STRUCT_P, then the alias code will assume that
the flushback can't alias scalars. This loses when you extract
scalars off a varargs list.
If you don't set MEM_IN_STRUCT_P, then the alias code will assume
that the flushback can't alias structs. THis loses when you
extract structs off a varargs list.
Basically you can't win. The way we do flushbacks creates an
aliasing situation that's going to cause problems somewhere.
Thus the easiest solution is a blockage insn.
jeff