[ping^2][PATCH][2 of 2] RTL expansion for zero sign extension elimination with VRP

[Kugan <kugan.vivekanandarajah@linaro.org>]

Hi Eric,

Can you please help to review the general idea and this patch for  zero 
sign extension elimination with VRP?


Thanks,
Kugan

On 17/06/13 11:01, Kugan wrote:
> Can you please help to review this patch? Richard reviewed the original
> patch and asked it to be split into two parts. Also, he wanted a review
> from RTL maintainers for the RTL changes.
>
> Thanks,
> Kugan
>
> On 03/06/13 11:46, Kugan wrote:
>> Hi,
>>
>> This patch  removes some of the redundant sign/zero extensions using
>> value range information during RTL expansion.
>>
>> When GIMPLE_ASSIGN stmts with LHS type smaller than word is expanded to
>> RTL, if we can prove that RHS expression value can always fit in LHS
>> type and there is no sign conversion, truncation and extension to fit
>> the type is redundant. For a SUBREG_PROMOTED_VAR_P, Subreg and Zero/sign
>> extensions are therefore redundant.
>>
>> For example, when an expression is evaluated and it's value is assigned
>> to variable of type short, the generated RTL would look something like
>> the following.
>>
>> (set (reg:SI 110)
>>                   (zero_extend:SI (subreg:HI (reg:SI 117) 0)))
>>
>> However, if during value range propagation, if we can say for certain
>> that the value of the expression which is present in register 117 is
>> within the limits of short and there is no sign conversion, we do not
>> need to perform the subreg and zero_extend; instead we can generate the
>> following RTl.
>>
>> (set (reg:SI 110)
>>                   (reg:SI 117)))
>>
>> Same could be done for other assign statements.
>>
>> This patch is based on the earlier attempt posted in
>> http://gcc.gnu.org/ml/gcc-patches/2013-05/msg00610.html and addresses
>> the review comments of  Richard Biener. I am post-processing the
>> expand_expr_real_2 output in expand_gimple_stmt though. Reason for this
>> is that I would like to process all the possible assignment stmts, not
>> just  CASE_CONVERT case and/or the REDUCE_BITFIELD.
>>
>> This change along with expansion improve the geomean of spec2k int
>> benchmark with ref by about ~3.5% on an arm chromebook.
>>
>> Tested  on X86_64 and ARM.
>>
>> I would like review comments on this.
>>
>> Thanks,
>> Kugan
>>
>>
>> +2013-06-03  Kugan Vivekanandarajah  <kuganv@linaro.org>
>> +
>> +    * gcc/dojump.c (do_compare_and_jump): generates rtl without
>> +    zero/sign extension if redundant.
>> +    * gcc/cfgexpand.c (expand_gimple_stmt_1): Likewise.
>> +    * gcc/gimple.c (gimple_assign_is_zero_sign_ext_redundant) : New
>> +    function.
>> +    * gcc/gimple.h (gimple_assign_is_zero_sign_ext_redundant) : New
>> +    function definition.
>> +
>>
>>
>>
>>
>>
>>
>>
>