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From: "vekumar at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/64946] [AArch64] gcc.target/aarch64/vect-abs-compile.c - "abs" vectorization fails for char/short types
Date: Thu, 26 Feb 2015 16:42:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64946

--- Comment #9 from vekumar at gcc dot gnu.org ---
This match.pd pattern vectorizes the PR but works only with -fwrapv.

(simplify
 ( convert (abs (convert@1 @0)))
 ( if (INTEGRAL_TYPE_P (type)
      /* We check for type compatibility between @0 and @1 below,
         so there's no need to check that @1/@3 are integral types.  */
      && INTEGRAL_TYPE_P (TREE_TYPE (@0))
      && INTEGRAL_TYPE_P (TREE_TYPE (@1))
      /* The precision of the type of each operand must match the
         precision of the mode of each operand, similarly for the
         result.  */
      && (TYPE_PRECISION (TREE_TYPE (@0))
          == GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (@0))))
      && (TYPE_PRECISION (TREE_TYPE (@1))
          == GET_MODE_PRECISION (TYPE_MODE (TREE_TYPE (@1))))
      && TYPE_PRECISION (type) == GET_MODE_PRECISION (TYPE_MODE (type))
      /* The inner conversion must be a widening conversion.  */
      && TYPE_PRECISION (TREE_TYPE (@1)) > TYPE_PRECISION (TREE_TYPE (@0))
      && ((GENERIC
           && (TYPE_MAIN_VARIANT (TREE_TYPE (@0))
               == TYPE_MAIN_VARIANT (type)))
          || (GIMPLE
              && types_compatible_p (TREE_TYPE (@0), type))))
   (if (TYPE_OVERFLOW_WRAPS (TREE_TYPE (@0)))
    (abs @0))))

For default cases (when no -fwrapv is given), doing ABSE_EXPR(shorttype) will
invoke undefined behaviour when value is -32678. similarly for signed char min.

As per Richard suggestion we need to move to a new tree code ABSU_EXPR to do
this type of folding optimization.