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[openrisc] PC as GPR?

To: openrisc@opencores.org
Subject: [openrisc] PC as GPR?
From: Andreas Bombe <bombe@informatik.tu-muenchen.de>
Date: Wed, 20 Feb 2002 16:30:14 +0100
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(List ate my email - this is a resend.)

Is there a specific reason why the PC is not addressable like a general
purpose register (i.e. make r31 be the PC)?

Disadvantage: losing one GPR (not that painful with 32 regs).

Advantages:  Jmp becomes an alias for mov, frees one opcode.  Computable
branch via add/sub.  PC relative addressing for load/store (no base
register needed for position independent code).


And a wishlist item:  The architecture manual in PDF form seems not to
be up to date wrt the Word doc, according to CVS.  Word stuff is
unwieldy, can a current PDF be generated?

Also, did I miss something from looking over the manual or is there
really no pre-decrement/post-increment addressing mode?  Or is the PDF
manual really obsolete?

-- 
Andreas Bombe <bombe@informatik.tu-muenchen.de>    DSA key 0x04880A44
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Follow-Ups:
- Re: [openrisc] PC as GPR?
  - From: Damjan Lampret <lampret@opencores.org>
- Re: [openrisc] PC as GPR?
  - From: "David Feustel" <dfeustel@mindspring.com>

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