On 09/08/2016 02:59 PM, Jason Merrill wrote:
On Thu, Sep 8, 2016 at 11:55 AM, Joseph Myers <jos...@codesourcery.com> wrote:
> On Thu, 8 Sep 2016, Jason Merrill wrote:
>
>> Various places in GCC use negate, bit-and and compare to test whether
>> an integer is a power of 2, but I think it would be clearer for this
>> test to be wrapped in a function.
>
> (x & -x) == x is also true for 0. Whatever the correct function semantics
> for 0, the comment needs to reflect them.
Yep, I was just realizing that, too. This much larger patch introduces:
least_bit_hwi: (x & -x)
pow2_or_zerop: (x & -x) == x
pow2p_hwi: x && x == (x & -x)
ctz_or_zero: floor_log2 (x & -x)
and replaces these patterns accordingly. I'm not at all attached to the names.
Tested x86_64-pc-linux-gnu.
hwint.diff
commit 4b76501b72f3953ac57cb077b4e25a90afb6d9a9
Author: Jason Merrill <ja...@redhat.com>
Date: Thu Sep 8 13:10:12 2016 -0400
Add inline functions for various bitwise operations.
* hwint.h (least_bit_hwi, pow2_or_zerop, pow2p_hwi, ctz_or_zero):
New.
* hwint.c (exact_log2): Use pow2p_hwi.
(ctz_hwi, ffs_hwi): Use least_bit_hwi.
* alias.c (memrefs_conflict_p): Use pow2_or_zerop.
* builtins.c (get_object_alignment_2, get_object_alignment)
(get_pointer_alignment, fold_builtin_atomic_always_lock_free): Use
least_bit_hwi.
* calls.c (compute_argument_addresses, store_one_arg): Use
least_bit_hwi.
* cfgexpand.c (expand_one_stack_var_at): Use least_bit_hwi.
* combine.c (force_to_mode): Use least_bit_hwi.
* emit-rtl.c (set_mem_attributes_minus_bitpos, adjust_address_1):
Use least_bit_hwi.
* expmed.c (synth_mult, expand_divmod): Use ctz_or_zero, ctz_hwi.
(init_expmed_one_conv): Use pow2p_hwi.
* fold-const.c (round_up_loc, round_down_loc): Use pow2_or_zerop.
(fold_binary_loc): Use pow2p_hwi.
* function.c (assign_parm_find_stack_rtl): Use least_bit_hwi.
* gimple-fold.c (gimple_fold_builtin_memory_op): Use pow2p_hwi.
* gimple-ssa-strength-reduction.c (replace_ref): Use least_bit_hwi.
* hsa-gen.c (gen_hsa_addr_with_align, hsa_bitmemref_alignment):
Use least_bit_hwi.
* ipa-cp.c (ipcp_alignment_lattice::meet_with_1): Use least_bit_hwi.
* ipa-prop.c (ipa_modify_call_arguments): Use least_bit_hwi.
* omp-low.c (oacc_loop_fixed_partitions)
(oacc_loop_auto_partitions): Use least_bit_hwi.
* rtlanal.c (nonzero_bits1): Use ctz_or_zero.
* stor-layout.c (place_field): Use least_bit_hwi.
* tree-pretty-print.c (dump_generic_node): Use pow2p_hwi.
* tree-sra.c (build_ref_for_offset): Use least_bit_hwi.
* tree-ssa-ccp.c (ccp_finalize): Use least_bit_hwi.
* tree-ssa-math-opts.c (bswap_replace): Use least_bit_hwi.
* tree-ssa-strlen.c (handle_builtin_memcmp): Use pow2p_hwi.
* tree-vect-data-refs.c (vect_analyze_group_access_1)
(vect_grouped_store_supported, vect_grouped_load_supported)
(vect_permute_load_chain, vect_shift_permute_load_chain)
(vect_transform_grouped_load): Use pow2p_hwi.
* tree-vect-generic.c (expand_vector_divmod): Use ctz_or_zero.
* tree-vect-patterns.c (vect_recog_divmod_pattern): Use ctz_or_zero.
* tree-vect-stmts.c (vectorizable_mask_load_store): Use
least_bit_hwi.
* tsan.c (instrument_expr): Use least_bit_hwi.
* var-tracking.c (negative_power_of_two_p): Use pow2_or_zerop.
I was briefly worried about some of the expmed changes, but managed to
convince myself they were correct.
Ok for the trunk.
Thanks,
jeff
