Re: [PATCH][ARM][cleanup] Use IN_RANGE more often

[Kyrill Tkachov <kyrylo.tkachov@arm.com>]

On 18/04/15 15:18, Richard Earnshaw wrote:
> On 15/04/15 16:22, Kyrill Tkachov wrote:
>> Hi all,
>>
>> This patch goes through the arm backend and replaces expressions of the
>> form
>> a >= lo && a <= hi with IN_RANGE (a, lo, hi) which is that tiny bit smaller
>> and easier to read in my opinion. I guess there's also a chance it might
>> make
>> things infinitesimally faster since IN_RANGE evaluates 'a' only once.
>> The patch also substitutes expressions like a > hi || a < lo with
>> !IN_RANGE (a, lo, hi) which, again, conveys the intended meaning more
>> clearly.
>> I tried to make sure not to introduce any off-by-one errors and testing
>> caught some that I had made while writing these.
>>
>> Bootstrapped and tested arm-none-linux-gnueabihf. Built and run SPEC2006
>> succesfully.
>>
>> Ok for trunk once 5.1 is released?
>>
> I think this is pretty obvious for those cases where the type of the
> range is [unsigned] HOST_WIDE_INT, but much less obvious for those cases
> where the type is just int, or unsigned.  Cases that I think need more
> careful examination include vfp3_const_double_index and
> aapcs_vfp_is_call_or_return_candidate, but I haven't gone through every
> instance to check whether there are more cases.

The definition and comment on IN_RANGE in system.h is:
/* A macro to determine whether a VALUE lies inclusively within a
    certain range without evaluating the VALUE more than once.  This
    macro won't warn if the VALUE is unsigned and the LOWER bound is
    zero, as it would e.g. with "VALUE >= 0 && ...".  Note the LOWER
    bound *is* evaluated twice, and LOWER must not be greater than
    UPPER.  However the bounds themselves can be either positive or
    negative.  */
#define IN_RANGE(VALUE, LOWER, UPPER) \
   ((unsigned HOST_WIDE_INT) (VALUE) - (unsigned HOST_WIDE_INT) (LOWER) \
    <= (unsigned HOST_WIDE_INT) (UPPER) - (unsigned HOST_WIDE_INT) (LOWER))

Since it works on positive or negative bounds, I'd think it would work on
signed numbers, wouldn't it?

>
> I'd be particularly concerned about these if the widening of the result
> caused a code quality regression on a native 32-bit machine (since HWI
> is a 64-bit type).

That being said, I see a 0.6% size increase on cc1 built on a native arm-linux
system. This seems like a not trivial increase to me. If that is not acceptable
then we can drop this patch.

Thanks,
Kyrill

>
> R.
>
>> Thanks,
>> Kyrill
>>
>> 2015-04-15  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
>>
>>      * config/arm/arm.md (*zeroextractsi_compare0_scratch): Use IN_RANGE
>>      instead of two compares.
>>      (*ne_zeroextractsi): Likewise.
>>      (*ite_ne_zeroextractsi): Likewise.
>>      (load_multiple): Likewise.
>>      (store_multiple): Likewise.
>>      * config/arm/arm.h (IS_IWMMXT_REGNUM): Likewise.
>>      (IS_IWMMXT_GR_REGNUM): Likewise.
>>      (IS_VFP_REGNUM): Likewise.
>>      * config/arm/arm.c (arm_return_in_memory): Likewise.
>>      (aapcs_vfp_is_call_or_return_candidate): Likewise.
>>      (thumb_find_work_register): Likewise.
>>      (thumb2_legitimate_address_p): Likewise.
>>      (arm_legitimate_index_p): Likewise.
>>      (thumb2_legitimate_index_p): Likewise.
>>      (thumb1_legitimate_address_p): Likewise.
>>      (thumb_legitimize_address): Likewise.
>>      (vfp3_const_double_index): Likewise.
>>      (neon_immediate_valid_for_logic): Likewise.
>>      (bounds_check): Likewise.
>>      (load_multiple_sequence): Likewise.
>>      (store_multiple_sequence): Likewise.
>>      (offset_ok_for_ldrd_strd): Likewise.
>>      (callee_saved_reg_p): Likewise.
>>      (thumb2_emit_strd_push): Likewise.
>>      (arm_output_load_gr): Likewise.
>>      (arm_vector_mode_supported_p): Likewise.
>>      * config/arm/neon.md (ashldi3_neon_noclobber): Likewise.
>>      (ashrdi3_neon_imm_noclobber): Likewise.
>>      (lshrdi3_neon_imm_noclobber): Likewise.
>>      * config/arm/thumb1.md (*thumb1_addsi3): Likewise.
>>      * config/arm/thumb2.md (define_peephole2's after orsi_not_shiftsi_si):
>>      Likewise.