From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeffrey A Law <law@hurl.cygnus.com>
To: egcs@cygnus.com
Subject: Re: double alignment patch for x86
Date: Tue, 19 Aug 1997 03:52:10 -0000
Message-ID: <199708190343.XAA13881@tweedledumb.cygnus.com>
In-reply-to: double alignment patch for x86
X-SW-Source: 1997-08/0127.html
Message-ID: <19970819035210.6LwX3sik6weFIzDTc8Jxt2aAeyw9J1kk2t5ED6KOzso@z>

  In message <199708190343.XAA13881@tweedledumb.cygnus.com>you write:
  > | That's one way to approach the problem, but it results in an extra insn t
  > o
  > | mask off the low bits of the stack in the prologue.
  > 
  > I meant just raise STACK_ALIGNMENT to 64.  Aligning it at runtime would
  > be a disaster on the x86, due to all arguments being pushed on the stack,
  > and having few registers.
Oh.  Slight mis-communication.

However, raising STACK_ALIGNMENT would still lose if the OS and friends
don't keep the stack suitably aligned -- some of Kenner's changes from last
year in combine.c will blow up badly (see REG_POINTER_ALIGNMENT changes from
1996).

I had the distinct pleasure of analyzing half a dozen of these kinds of
problems because the ABI on the PA specifies a 64byte alignment, but the
OS+crt0.o only provides an 8 byte alignment.  The result was combine
would remove instructions it throught were redundant, but which were
really necessary.

jeff