[PATCH][10/n] Remove GENERIC stmt combining from SCCVN

[Kyrill Tkachov]

On 06/07/15 15:46, Richard Biener wrote:
> On Mon, 6 Jul 2015, Kyrill Tkachov wrote:
>
>> Hi Richard,
>>
>> On 01/07/15 14:03, Richard Biener wrote:
>>> This merges the complete comparison patterns from the match-and-simplify
>>> branch, leaving incomplete implementations of fold-const.c code alone.
>>>
>>> Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.
>>>
>>> Richard.
>>>
>>> 2015-07-01  Richard Biener  <rguenther@suse.de>
>>>
>>> 	* fold-const.c (fold_comparison): Move X - Y CMP 0 -> X CMP Y,
>>> 	X * C1 CMP 0 -> X CMP 0, X CMP X, ~X CMP ~Y -> Y CMP X and
>>> 	~X CMP C -> X CMP' ~C to ...
>>> 	* match.pd: ... patterns here.
>>>
>>>
>>>    +/* Transform comparisons of the form X - Y CMP 0 to X CMP Y.
>>> +   ??? The transformation is valid for the other operators if overflow
>>> +   is undefined for the type, but performing it here badly interacts
>>> +   with the transformation in fold_cond_expr_with_comparison which
>>> +   attempts to synthetize ABS_EXPR.  */
>>> +(for cmp (eq ne)
>>> + (simplify
>>> +  (cmp (minus @0 @1) integer_zerop)
>>> +  (cmp @0 @1)))
>> This broke some tests on aarch64:
>> FAIL: gcc.target/aarch64/subs.c scan-assembler subs\tw[0-9]
>> FAIL: gcc.target/aarch64/subs1.c scan-assembler subs\tw[0-9]+, w[0-9]+,
>> w[0-9]+
>> FAIL: gcc.target/aarch64/subs1.c scan-assembler subs\tw[0-9]+, w[0-9]+,
>> w[0-9]+, lsl 3
>> FAIL: gcc.target/aarch64/subs1.c scan-assembler subs\tx[0-9]+, x[0-9]+,
>> x[0-9]+
>> FAIL: gcc.target/aarch64/subs1.c scan-assembler subs\tx[0-9]+, x[0-9]+,
>> x[0-9]+, lsl 3
>>
>> To take subs.c as an example:
>> There's something odd going on:
>> The X - Y CMP 0 -> X CMP Y transformation gets triggered only for the int case
>> but
>> not the long long case, but the int case (foo) is the place where the rtl ends
>> up being:
>>
>> (insn 9 4 10 2 (set (reg/v:SI 74 [ l ])
>>          (minus:SI (reg/v:SI 76 [ x ])
>>              (reg/v:SI 77 [ y ]))) subs.c:9 254 {subsi3}
>>       (nil))
>> (insn 10 9 11 2 (set (reg:CC 66 cc)
>>          (compare:CC (reg/v:SI 76 [ x ])
>>              (reg/v:SI 77 [ y ])))
>>
>> instead of the previous:
>>
>> (insn 9 4 10 2 (set (reg/v:SI 74 [ l ])
>>          (minus:SI (reg/v:SI 76 [ x ])
>>              (reg/v:SI 77 [ y ]))) subs.c:9 254 {subsi3}
>>
>> (insn 10 9 11 2 (set (reg:CC 66 cc)
>>          (compare:CC (reg/v:SI 74 [ l ])
>>              (const_int 0 [0])))
>>
>>
>> so the tranformed X CMP Y does not get matched by combine into a subs.
>> Was the transformation before the patch in fold-const.c not getting triggered?
> It was prevented from getting triggered by restricting the transform
> to single uses (a fix I am testing right now).
>
> Note that in case you'd write
>
>    int l = x - y;
>    if (l == 0)
>      return 5;
>
>    /* { dg-final { scan-assembler "subs\tw\[0-9\]" } } */
>    z = x - y ;
>
> the simplification will happen anyway because the redundancy
> computing z has not yet been eliminated (a reason why such
> single-use checks are not 100% the very much "correct" thing to do).

Ok, thanks. Andreas pointed out PR 66739 to me. I had not noticed it.
Sorry for the noise.

Kyrill

>
>> In aarch64 we have patterns to match:
>>    [(set (reg:CC_NZ CC_REGNUM)
>>      (compare:CC_NZ (minus:GPI (match_operand:GPI 1 "register_operand" "r")
>>                    (match_operand:GPI 2 "register_operand" "r"))
>>                 (const_int 0)))
>>     (set (match_operand:GPI 0 "register_operand" "=r")
>>      (minus:GPI (match_dup 1) (match_dup 2)))]
>>
>>
>> Should we add a pattern to match:
>>    [(set (reg:CC CC_REGNUM)
>>      (compare:CC (match_operand:GPI 1 "register_operand" "r")
>>                     (match_operand:GPI 2 "register_operand" "r")))
>>     (set (match_operand:GPI 0 "register_operand" "=r")
>>      (minus:GPI (match_dup 1) (match_dup 2)))]
>>
>> as well?
> No, I don't think so.
>
> Richard.
>
>> Kyrill
>>
>>> +
>>> +/* Transform comparisons of the form X * C1 CMP 0 to X CMP 0 in the
>>> +   signed arithmetic case.  That form is created by the compiler
>>> +   often enough for folding it to be of value.  One example is in
>>> +   computing loop trip counts after Operator Strength Reduction.  */
>>> +(for cmp (tcc_comparison)
>>> +     scmp (swapped_tcc_comparison)
>>> + (simplify
>>> +  (cmp (mult @0 INTEGER_CST@1) integer_zerop@2)
>>> +  /* Handle unfolded multiplication by zero.  */
>>> +  (if (integer_zerop (@1))
>>> +   (cmp @1 @2))
>>> +  (if (ANY_INTEGRAL_TYPE_P (TREE_TYPE (@0))
>>> +       && TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0)))
>>> +   /* If @1 is negative we swap the sense of the comparison.  */
>>> +   (if (tree_int_cst_sgn (@1) < 0)
>>> +    (scmp @0 @2))
>>> +   (cmp @0 @2))))
>>> +
>>> +/* Simplify comparison of something with itself.  For IEEE
>>> +   floating-point, we can only do some of these simplifications.  */
>>> +(simplify
>>> + (eq @0 @0)
>>> + (if (! FLOAT_TYPE_P (TREE_TYPE (@0))
>>> +      || ! HONOR_NANS (TYPE_MODE (TREE_TYPE (@0))))
>>> +  { constant_boolean_node (true, type); }))
>>> +(for cmp (ge le)
>>> + (simplify
>>> +  (cmp @0 @0)
>>> +  (eq @0 @0)))
>>> +(for cmp (ne gt lt)
>>> + (simplify
>>> +  (cmp @0 @0)
>>> +  (if (cmp != NE_EXPR
>>> +       || ! FLOAT_TYPE_P (TREE_TYPE (@0))
>>> +       || ! HONOR_NANS (TYPE_MODE (TREE_TYPE (@0))))
>>> +   { constant_boolean_node (false, type); })))
>>> +
>>> +/* Fold ~X op ~Y as Y op X.  */
>>> +(for cmp (tcc_comparison)
>>> + (simplify
>>> +  (cmp (bit_not @0) (bit_not @1))
>>> +  (cmp @1 @0)))
>>> +
>>> +/* Fold ~X op C as X op' ~C, where op' is the swapped comparison.  */
>>> +(for cmp (tcc_comparison)
>>> +     scmp (swapped_tcc_comparison)
>>> + (simplify
>>> +  (cmp (bit_not @0) CONSTANT_CLASS_P@1)
>>> +  (if (TREE_CODE (@1) == INTEGER_CST || TREE_CODE (@1) == VECTOR_CST)
>>> +   (scmp @0 (bit_not @1)))))
>>> +
>>> +
>>>    /* Unordered tests if either argument is a NaN.  */
>>>    (simplify
>>>     (bit_ior (unordered @0 @0) (unordered @1 @1))
>>>
>>