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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/64829] [ARM] ICE at -O3 in vect_get_vec_def_for_stmt_copy
Date: Wed, 28 Jan 2015 14:06:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64829

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
In fact we recognize a widening shift but it gets dropped on the floor:

t.c:48:2: note: ------>vectorizing statement: result_15 = val0_14 << 4;

t.c:48:2: note: ------>vectorizing statement: _17 = val1_16(D) - val0_14;

huh?  The issue that we hit is that we vectorized the def of val0_14
with ncopies == 1 but now require two copies of it when vectorizing
val1_16(D) - val0_14.  So maybe the shift issue is unrelated.

Sofar we have

  vect__13.17_155 = MEM[(const Uint8 *)vectp_pCornerPoint0.15_153];
  _13 = *pCornerPoint0_48;
  vect__41.18_156 = [vec_unpack_lo_expr] vect__13.17_155;
  vect__41.18_157 = [vec_unpack_hi_expr] vect__13.17_155;
  val0_14 = (Sint32) _13;

Thus we widen a char load to an int but the vectorized version widens to
an unsigned short only.  That's probably because of the consumer

  result_15 = val0_14 << 4;

which was pattern detected as widening shift.  But unfortunately that isn't
the only one and we forgot

  _17 = val1_16(D) - val0_14;

which then results in the ICE.

Index: gcc/tree-vect-patterns.c
===================================================================
--- gcc/tree-vect-patterns.c    (revision 220205)
+++ gcc/tree-vect-patterns.c    (working copy)
@@ -1732,9 +1732,11 @@ vect_recog_widen_shift_pattern (vec<gimp
   if (TREE_CODE (oprnd0) != SSA_NAME || TREE_CODE (oprnd1) != INTEGER_CST)
     return NULL;

-  /* Check operand 0: it has to be defined by a type promotion.  */
-  if (!type_conversion_p (oprnd0, last_stmt, false, &half_type0, &def_stmt0,
-                          &promotion)
+  /* Check operand 0: it has to be defined by a type promotion and it
+     should be only used by the shift.  */
+  if (!has_single_use (oprnd0)
+      || !type_conversion_p (oprnd0, last_stmt, false, &half_type0,
&def_stmt0,
+                            &promotion)
       || !promotion)
      return NULL;