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Re: PATCH:[darwin] fix load of a misaligned double word

From: Bradley Lucier <lucier at math dot purdue dot edu>
To: Ulrich Weigand <Ulrich dot Weigand at de dot ibm dot com>
Cc: Bradley Lucier <lucier at math dot purdue dot edu>, Geoff Keating <geoffk at desire dot geoffk dot org>, amodra at bigpond dot net dot au, gcc-patches at gcc dot gnu dot org, pinskia at physics dot uc dot edu, Hartmut Penner <HPENNER at de dot ibm dot com>, dje at watson dot ibm dot com, fjahanian at apple dot com
Date: Wed, 25 Feb 2004 13:09:32 -0500
Subject: Re: PATCH:[darwin] fix load of a misaligned double word
References: <OF70C30FAC.BBBD64EA-ONC1256E44.0020862B@de.ibm.com>

On Feb 24, 2004, at 1:07 AM, Ulrich Weigand wrote:

Geoff Keating wrote:

Disallowing both reverts back to gcc-3.3 behaviour, which loses
performance on certain code.  Allowing both means that "offset & 3"
gpr loads/stores must be fixed some other way.  Now this is where I
start to handwave.  What should be done about "some other way"?
Hartmut's reload patterns, perhaps with tighter reg constraints?
Please give us your thoughts on this.

We should allow them. "Some other way" is to use constraints.


However, constraints are only evaluated for insns already existing
before reload.  The insns reload itself generates are not checked
against any constraints -- it is assumed that any move-type insn
(with legitimate operands) will be valid, *or else* there will be
a secondary reload to perform the move.

Perhaps the insns that reload itself generates should be checked against constraints (or perhaps that's what a secondary reload is, I don't know).

Brad

References:
- Re: PATCH:[darwin] fix load of a misaligned double word
  - From: Ulrich Weigand

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