>> This patch is to handle simplification of plusminus-mult-with-convert
>> expression
>> as ((T) X) +- ((T) Y), in which at least one of (X, Y) is result of
>> multiplication.
>> This is done in forwprop pass. We try to transform it to (T) (X +- Y), and
>> resort
>> to gimple-matcher to fold (X +- Y) instead of manually code pattern
>> recognition.
>
>I still don't like the complete new function with all its correctness
>issues - the existing
>fold_plusminus_mult_expr was difficult enough to get correct for
>corner cases and
>we do have a set of match.pd patterns (partly?) implementing its transforms.
>
>Looking at
>
>+unsigned goo (unsigned m_param, unsigned n_param)
>+{
>+ unsigned b1 = m_param * (n_param + 2);
>+ unsigned b2 = m_param * (n_param + 1);
>+ int r = (int)(b1) - (int)(b2);
>
>it seems we want to simplify (signed)A - (signed)B to
>(signed)(A - B) if A - B "simplifies"? I guess
>
>(simplify
> (plusminus (nop_convert @0) (nop_convert? @1))
> (convert (plusminus! @0 @1)))
>
>probably needs a swapped pattern or not iterate over plus/minus
>to handle at least one converted operand and avoid adding
>a (plus @0 @1) -> (convert (plus! @0 @1)) rule.
>
>Even
>
>(simplify
> (minus (nop_convert @0) (nop_convert @1))
> (convert (minus! @0 @1)))
>
>seems to handle all your testcases already (which means
>they are all the same and not very exhaustive...)
Yes. This is much simpler.
Thanks,
Feng
>Richard.
>
>
>> Regards,
>> Feng
>> ---
>> 2020-09-03 Feng Xue <f...@os.amperecomputing.com>
>>
>> gcc/
>> PR tree-optimization/94234
>> * tree-ssa-forwprop.c (simplify_plusminus_mult_with_convert): New
>> function.
>> (fwprop_ssa_val): Move it before its new caller.
>> (pass_forwprop::execute): Add call to
>> simplify_plusminus_mult_with_convert.
>>
>> gcc/testsuite/
>> PR tree-optimization/94234
>> * gcc.dg/pr94234-3.c: New test.
>
