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Re: combination of read/write and earlyclobber constraint modifier


On 02-07-14 11:36, Marc Glisse wrote:
(did you drop the lists on purpose?)


That was a glitch, sorry.
[ Adds list back ]

Thanks,
- Tom

On Wed, 2 Jul 2014, Tom de Vries wrote:

An earlyclobber operand X prevents *other* input operands from using the same
register, but that does not include X itself (if it is using +) or operands
explicitly using a matching constraint for X. At least that's how I
understand it.

Right, that's another interpretation, which would require a clarification in
the documentation

Sure, improving the doc is always good.

I'm fine with either forbidding &= (as proposed here:
https://gcc.gnu.org/ml/gcc-patches/2014-07/msg00094.html ) or clarifying the
semantics in the documentation.

+ is essentially a shortcut for = with a matching constraint in the input
operand, so I don't think it is the right level to forbid anything.



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