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Re: SUBREG_BYTE question

From: Graham Stott <grahams at redhat dot com>
To: Bernd Schmidt <bernds at redhat dot com>
Cc: gcc at gcc dot gnu dot org
Date: Tue, 26 Feb 2002 13:46:13 +0000
Subject: Re: SUBREG_BYTE question
References: <Pine.LNX.4.33.0202261330510.32394-100000@host140.cambridge.redhat.com>

Bernd Schmidt wrote:
> 
> I need to know the exact meaning of the SUBREG_BYTE field of a SUBREG.
> 
> Suppose I have a big-endian target, an SImode (which is the word size)
> register, and I want to use the part of the register in a narrower mode.
> Should SUBREG_BYTE be zero, or should it be equal to the offset that
> would be used if the value were in memory?

I think it also depends on WORDS_BIG_ENDIAN which controls whether word 0
is most or significant word.

> 
> The problem I have is that I've got two testcases, and in one of these I
> get (subreg:HI (reg:SI xyz) 0) for the lowpart, and in the other I get
> (subreg:QI (reg:SI abc) 3).  Fixing one breaks the other.  Which one is
> correct?
> 
> Bernd

Graham

References:
- SUBREG_BYTE question
  - From: Bernd Schmidt

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