From: "Ronald G. Minnich" <rminnich@lanl.gov>
To: 9fans@cse.psu.edu
Subject: [9fans] got it
Date: Thu, 10 Mar 2005 11:34:44 -0700 [thread overview]
Message-ID: <Pine.LNX.4.58.0503101129220.12217@enigma.lanl.gov> (raw)
an optimization is dumping onto another, it seems.
on arm.
ulong *x, y[64];
x = y;
*x++ = 1;
*x++ = 2;
assembly gives:
MOVW $y-260(SP),R3
MOVW $1, R2
MOVW.P R2, $4(R3)
so the 260 puts you two words before the first element of Y, I'm guessing
(otherwise it would be y-252, right? 63*4). Then it does a pre-increment
and offset by 4, which puts you right at the first element of y.
Which all fails badly if you're setting x to a constant, as in constant
page table value in memory for startup.
That's my reading anyway.
I'm still unsure, all I know is the .s code looks wrong to me for the l.s
changes I'm making. (I'm too lazy to write assembly, I try to have C
compilers do it for me. Usually works. Maybe not this time.)
ron
next reply other threads:[~2005-03-10 18:34 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-03-10 18:34 Ronald G. Minnich [this message]
2005-03-10 18:49 ` Russ Cox
2005-03-10 21:00 ` Ronald G. Minnich
2005-03-10 21:10 ` Ronald G. Minnich
2005-03-10 18:39 Ben Huntsman
2005-03-10 20:58 ` Ronald G. Minnich
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