https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109967
Davin McCall <davmac at davmac dot org> changed:
What |Removed |Added
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CC| |davmac at davmac dot org
--- Comment #3 from Davin McCall <davmac at davmac dot org> ---
-fdisable-tree-cunroll avoids it.
This is the take of someone who is new to poking GCC internals, so take this
with a grain of salt, but:
It looks like cunroll duplicates (partially unrolls, I suppose) the inner loop,
meaning that `g' is live in two disjoint ranges, with a CLOBBER between them.
Then later passes (fre5, but disabling it doesn't seem to help) recognise that
&g and &g are the same in both ranges and so use a single temporary for both.
This confuses cfgexpand (as Andrew Pinski notes) because the memory dereference
of the temporary isn't seen as an access of g (in
add_scope_conflicts()/add_scope_conflicts_1()/visit_conflict()).
I don't understand the IR semantics well enough to know the right fix - perhaps
cunroll should be removing the clobber (does a clobber affect storage lifetime
or only value?), or perhaps cfgexpand should be more conservative when it sees
a memory access.
