From: Richard Henderson <rth@redhat.com>
To: Mohamed Shafi <shafitvm@gmail.com>
Cc: GCC <gcc@gcc.gnu.org>
Subject: Re: Need help in deciding the instruction set for a new target.
Date: Mon, 23 Aug 2010 22:20:00 -0000 [thread overview]
Message-ID: <4C72D909.9030204@redhat.com> (raw)
In-Reply-To: <AANLkTimKoa7xNV4dgqQdysJGB6bc2_O7bQrKruiMXhEL@mail.gmail.com>
On 08/23/2010 11:05 AM, Mohamed Shafi wrote:
> sub.s32 srcdstGP, #imm16 // signed 16-bit register to immediate subtract
> sub.u32 srcdstGP, #imm16 // unsigned 16-bit register to immediate subtract
Having both of these is probably not useful. Bernd pointed
out that a 17-bit constant would be more useful. I'll point
out that if you have a signed constant then SUB and ADD tend
to be essentially identical as well.
Consider implementing "reverse subtract"
RSUB reg, #imm
as
reg = imm - reg
instead.
r~
prev parent reply other threads:[~2010-08-23 20:24 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-23 18:25 Mohamed Shafi
2010-08-23 19:00 ` Ian Lance Taylor
2010-08-23 20:24 ` Bernd Schmidt
2010-08-23 22:20 ` Richard Henderson [this message]
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