Hi,
As described in PR100499, loop niters analysis for "!=" now relies on
multiple_of_p which
so far is mostly implemented for no-overflow scenarios. This patch fixes the
issue by:
1. add new parameter to multiple_of_p indicating no-wrapping behavior in top
expression.
2. pass new argument to help multiple_of_p, for example, the case in
stor-layout.c.
3. adjust calls in number_of_iterations_ne by checking multiple_of_p without
dependence
on wrapping/no-wrapping behavior. It also corrects one issue in PR72817.
Noticed there are some improvements in ranger to help analysis of
multiple_of_p. For
TOP expression like "left op right", we would like to check if this specific op
wraps or not.
For example:
1. left (unsigned, multiple of 3) + 0xfffffffd: the result is multiple of 3 if
"+" wraps even if
right operand is not multiple of 3.
2. left (unsigned, multiple of 3) + 6: the result is not multiple of 3 if "+"
wraps even if the
right operand is multiple of 3.
So in the end, we might need ranger to tell if such operator wraps or not, i.e,
must_overflow,
must_not_overflow, may_overflow. Of course, we need to be conservative in the
last case.
Bootstrap and test on x86_64. Any comments?
Thanks,
bin
pr100499-20210520.txt
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