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Re: When is the hardware related register is allocated?

Quoting Feng LI <nemokingdom@gmail.com>:

So I suppose with (clobber (reg:CC FLAGS_REG)), the compiler
will be capable to know this register will be modified in this instruction and
apply proper behavior when necessary? 

Depends.  It will stop the compiler moving a FLAGS_REG setter and/or user
such that FLAGS_REG becomes live across your insn pattern.
But if you emit this pattern in a place where FLAGS_REG is already live
(e.g. when you generate it from some combiner pattern, or create it
via a split / peephole2 without FLAGS_REG clobber), there is a problem.

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