On 9/26/22 11:24, Aldy Hernandez via Gcc-patches wrote:
For [0 = x & MASK], we can determine that x is ~MASK. This is
something we're picking up in DOM thanks to maybe_set_nonzero_bits,
but is something we should handle natively.
This is a good example of how much easier to maintain the range-ops
entries are versus the ad-hoc pattern matching stuff we had to do
before. For the curious, compare the changes to range-op here,
versus maybe_set_nonzero_bits.
I'm leaving the call to maybe_set_nonzero_bits until I can properly
audit it to make sure we're catching it all in range-ops. It won't
hurt, since both set_range_info() and set_nonzero_bits() are
intersect operations, so we'll never lose information if we do both.
Tested on x86-64 Linux.
PR tree-optimization/107009
gcc/ChangeLog:
* range-op.cc (operator_bitwise_and::op1_range): Optimize 0 = x & MASK.
(range_op_bitwise_and_tests): New test.
Umm,
0 = x & MASK;
Just means that X has no bits set in MASK. So you can use it to set
nonzero-bits to ~MASK like your patch does and you can use that to
refine a result. So it's really the comment that is misleading/wrong.
jeff
