| Message ID | 20220926172441.3219466-1-aldyh@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [COMMITTED] Optimize [0 = x & MASK] in range-ops. | expand |
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
Le 26/09/2022 à 19:24, Aldy Hernandez via Gcc-patches a écrit : > For [0 = x & MASK], we can determine that x is ~MASK. > Suggestion: as AND is a bitwise operator, a X non-zero bit can be cleared for every bit at which the result is cleared and the MASK is set, so what you do here can be extended to non-zero result values.
diff --git a/gcc/range-op.cc b/gcc/range-op.cc index 072ebd32109..fc930f4d613 100644 --- a/gcc/range-op.cc +++ b/gcc/range-op.cc @@ -2951,6 +2951,15 @@ operator_bitwise_and::op1_range (irange &r, tree type, } if (r.undefined_p ()) set_nonzero_range_from_mask (r, type, lhs); + + // For 0 = op1 & MASK, op1 is ~MASK. + if (lhs.zero_p () && op2.singleton_p ()) + { + wide_int nz = wi::bit_not (op2.get_nonzero_bits ()); + int_range<2> tmp (type); + tmp.set_nonzero_bits (nz); + r.intersect (tmp); + } return true; } @@ -4612,6 +4621,15 @@ range_op_bitwise_and_tests () op_bitwise_and.op1_range (res, integer_type_node, i1, i2); ASSERT_TRUE (res == int_range<1> (integer_type_node)); + // For 0 = x & MASK, x is ~MASK. + { + int_range<2> zero (integer_zero_node, integer_zero_node); + int_range<2> mask = int_range<2> (INT (7), INT (7)); + op_bitwise_and.op1_range (res, integer_type_node, zero, mask); + wide_int inv = wi::shwi (~7U, TYPE_PRECISION (integer_type_node)); + ASSERT_TRUE (res.get_nonzero_bits () == inv); + } + // (NONZERO | X) is nonzero. i1.set_nonzero (integer_type_node); i2.set_varying (integer_type_node);