[PATCH AutoFDO/2]Treat ZERO as common profile probability/count

[bin.cheng]

Hi,
In new profile probability/count infra, we have different precision quality categories,
and probabilities/counts of different categories are not supposed to be compared or
calculated.  Though in general is an improvement, it introduces unexpected behavior.
Specifically, class profile_probablity and profile_count themselves are implemented
by comparing probabilities/counts against profile_count::zero().  while zero() is of
profile_precision category, it's always compared different to zero of other precision
categories including afdo.

I can see two ways fixing this: 1) Treat zero as a common probability/count regardless
of its category; 2) Provide an "is_zero" method rather than relying on "==" comparison
against probability_count::zero().  2) requires lots of code changes so I went with 1)
in this patch set.  This patch doesn't handle "always" but it might be.

This patch also corrects a minor issue where we try to invert an uninitialized value.

Bootstrap and test on x86_64 in patch set.  Is it OK?

Thanks,
bin

2018-10-31  Bin Cheng  <bin.cheng@linux.alibaba.com>

	* expmed.c (emit_store_flag_force): Use profile_probability::always.
	* profile-count.h (profile_probability::always): Add parameter.
	(profile_probability::operator==, profile_count::operator==): Treat
	ZERO as common probability/count regardless of its quality.
	(profile_probability::invert): Don't invert uninitialized probability.
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