Re: [trunk] Addition to subreg section of rtl.text.

[Ian Lance Taylor <iant at google dot com>]

Richard Sandiford <rsandifo@nildram.co.uk> writes:

> Kenneth Zadeck <zadeck@naturalbridge.com> writes:
>> Does every one agree that what i am adding is correct?
>>
>> kenny
>> Index: rtl.texi
>> ===================================================================
>> --- rtl.texi	(revision 133159)
>> +++ rtl.texi	(working copy)
>> @@ -1730,15 +1730,21 @@ are in @var{m}.
>>  Sometimes @var{m} is wider than the mode of @var{reg}.  These
>>  @code{subreg} expressions are often called @dfn{paradoxical}.  They are
>>  used in cases where we want to refer to an object in a wider mode but do
>> -not care what value the additional bits have.  The reload pass ensures
>> -that paradoxical references are only made to hard registers.
>> -
>> +not care what value the additional bits have.  The smaller register
>> +always overlaps the least significant bits of the larger register and
>> +the @var{bytenum} is always zero for paradoxical registers (even on big
>> +endian machines).  The reload pass ensures that paradoxical references
>> +are only made to hard registers.
>
> FWIW, I agree with the first sentence.  I'm not quite sure what you mean
> by the second though.  My understanding is that reload should never
> replace an operand with a subreg of a hard register; it should always
> reduce it to a "reg" rtx.  I think subregs should only appear after
> reload if they are part of an .md pattern (as in spe.md, for example).

He just copied the second sentence from the original.

Ian