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Re: Why Thumb-2 only allows very limited access to the PC?

From: Paul Brook <paul at codesourcery dot com>
To: Richard Earnshaw <rearnsha at arm dot com>
Cc: gcc at gcc dot gnu dot org, Carrot Wei <carrot at google dot com>
Date: Thu, 7 Jan 2010 11:05:11 +0000
Subject: Re: Why Thumb-2 only allows very limited access to the PC?
References: <7587b291001042342m1f5437faib94c55b20792f5d2@mail.gmail.com> <201001061826.51559.paul@codesourcery.com> <1262859782.31313.75.camel@e200601-lin.cambridge.arm.com>

On Thursday 07 January 2010, Richard Earnshaw wrote:
> On Wed, 2010-01-06 at 18:26 +0000, Paul Brook wrote:
> > On Wednesday 06 January 2010, Carrot Wei wrote:
> > > So thumb2 can also use the instructions similar to thumb1, right? It
> > > potentially has better performance and smaller code size.
> >
> > Technically yes, however in ARMv7 the relevant instruction (add.n <reg>,
> > pc) is deprecated.
> 
> Where'd you get that idea?
> 
> Annex D of the ARM ARM says that the 16-bit instructions that add SP and
> PC together (writing either SP or PC) are deprecated

You are correct, I misread that section.

Paul

References:
- Why Thumb-2 only allows very limited access to the PC?
  - From: Carrot Wei
- Re: Why Thumb-2 only allows very limited access to the PC?
  - From: Paul Brook
- Re: Why Thumb-2 only allows very limited access to the PC?
  - From: Richard Earnshaw

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