[Bug target/86771] [9 Regression] gfortran.dg/actual_array_constructor_1.f90 fails on arm after combine 2 insns to 2 insns patch

segher at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Mon Aug 20 20:58:00 GMT 2018


--- Comment #16 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Wilco from comment #14)
> Note there is also an issue with costs, if the cost is zero then it seems to
> behave like infinite cost.

0 means unknown cost.  Any known cost is treated as at least as good as
unknown cost.

> It would be better to properly cost an
> instruction sequence given there is a new interface for this now.


> If the
> cost is still zero, it could get the default cost rather than being treated
> like infinite cost, resulting in non-optimal replacements.

Treating unknown cost as minimal cost is still non-optimal.  It might work
better for your case of course.  But it means for example that combine will
modify parallels less often.

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