Hi!
On the following testcase we completely uselessly consume about 5.5GB
of RAM and lots of compile time. The problem is the code to avoid
exponential behavior of nonzero_bits/num_sign_bit_copies on binary
arithmetics rtxes, which causes us to recurse even when handling
of those rtxes is going to ignore those arguments.
So, this patch limits those only to the cases where we are going
to recurse on both arguments, for rtxes where we don't look at arguments
at all or where we only recurse on a single arguments it doesn't make
sense. On the testcase, one of the rtxes where the new predicates
return false but ARITHMETIC_P is true, is COMPARE, in particular
(compare:CCC (plus (x) (y)) (x)), where it is known even without
looking at the operands that only one bit is possibly non-zero and
number of sign bit copies is always 1. But without the patch we
needlessly recurse on x, which is set by another similar operation etc.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2016-02-01 Jakub Jelinek <jakub@redhat.com>
PR rtl-optimization/69592
* rtlanal.c (nonzero_bits_binary_arith_p): New inline function.
(cached_nonzero_bits): Use it instead of ARITHMETIC_P.
(num_sign_bit_copies_binary_arith_p): New inline function.
(cached_num_sign_bit_copies): Use it instead of ARITHMETIC_P.
* gcc.dg/pr69592.c: New test.