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


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))
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