* [COMMITTED] Optimize [0 = x & MASK] in range-ops.
@ 2022-09-26 17:24 Aldy Hernandez
2022-09-26 23:27 ` Jeff Law
2022-09-27 9:26 ` Mikael Morin
0 siblings, 2 replies; 3+ messages in thread
From: Aldy Hernandez @ 2022-09-26 17:24 UTC (permalink / raw)
To: GCC patches; +Cc: Andrew MacLeod, Aldy Hernandez
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.
---
gcc/range-op.cc | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
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);
--
2.37.1
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [COMMITTED] Optimize [0 = x & MASK] in range-ops.
2022-09-26 17:24 [COMMITTED] Optimize [0 = x & MASK] in range-ops Aldy Hernandez
@ 2022-09-26 23:27 ` Jeff Law
2022-09-27 9:26 ` Mikael Morin
1 sibling, 0 replies; 3+ messages in thread
From: Jeff Law @ 2022-09-26 23:27 UTC (permalink / raw)
To: gcc-patches
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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [COMMITTED] Optimize [0 = x & MASK] in range-ops.
2022-09-26 17:24 [COMMITTED] Optimize [0 = x & MASK] in range-ops Aldy Hernandez
2022-09-26 23:27 ` Jeff Law
@ 2022-09-27 9:26 ` Mikael Morin
1 sibling, 0 replies; 3+ messages in thread
From: Mikael Morin @ 2022-09-27 9:26 UTC (permalink / raw)
To: gcc-patches
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.
^ permalink raw reply [flat|nested] 3+ messages in thread
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