tree-optimization/124068 - fix missed AVX2 vectorization of shift

The following fixes a regression in AVX2 vectorization because on
trunk we are now correctly determine we can shorten a shift operation
but we never really bothered to check we can implement the
resulting operation.  With the patch we now check this.  For shifts
and rotates we have the choice between vector-vector and vector-scalar
operations which in the end depends on whether we perform SLP or not
and how the shift operand matches up.  The patch heuristically
assumes that constant or external shifts can be handled by vector-scalar
operations.

As we were not checking for target support was to allow recursive matching
other patterns, the following still errors on that side in case the
original operation was not supported by the target or it is binary and
the 2nd operand is a constant.  This helps avoiding regressions in
gcc.dg/vect/vect-over-widen-13.c and gcc.dg/vect/vect-div-bitmask-1.c
and gcc.target/aarch64/sve2/div-by-bitmask_1.c where the operation in
question is integer division.

	PR tree-optimization/124068
	* tree-vect-patterns.cc (target_has_vecop_for_code): Move
	earlier, add defaulted optab_subtype parameter.
	(vect_recog_over_widening_pattern): Check that the target
	supports the narrowed operation before committing to the
	pattern.

	* gcc.target/i386/vect-shift-1.c: New testcase.

diff --git a/gcc/testsuite/gcc.target/i386/vect-shift-1.c b/gcc/testsuite/gcc.target/i386/vect-shift-1.c
new file mode 100644 (file)
index 0000000..eb31ef4
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/vect-shift-1.c
@@ -0,0 +1,10 @@
+/* { dg-do compile { target avx2 } } */
+/* { dg-options "-O2 -mavx2 -mno-avx512f -fdump-tree-vect-details" } */
+
+void f (short* acc)
+{
+  for (unsigned char row = 0; row < 16; ++row)
+    acc[row] = acc[row] << row;
+}
+
+/* { dg-final { scan-tree-dump "optimized: loop vectorized" "vect" } } */

diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 97130206a2142a1b14d3858ccdc2345220345b0d..a5413ff00a3e6a070b163ce38231214d7c154480 100644 (file)
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -1036,6 +1036,17 @@ vect_reassociating_reduction_p (vec_info *vinfo,
   return true;
 }
 
+/* Return true iff the target has a vector optab implementing the operation
+   CODE on type VECTYPE with SUBTYPE.  */
+
+static bool
+target_has_vecop_for_code (tree_code code, tree vectype,
+                          enum optab_subtype subtype = optab_vector)
+{
+  optab voptab = optab_for_tree_code (code, vectype, subtype);
+  return voptab && can_implement_p (voptab, TYPE_MODE (vectype));
+}
+
 /* match.pd function to match
    (cond (cmp@3 a b) (convert@1 c) (convert@2 d))
    with conditions:
@@ -3160,16 +3171,36 @@ vect_recog_over_widening_pattern (vec_info *vinfo,
       && (code == PLUS_EXPR || code == MINUS_EXPR || code == MULT_EXPR))
     op_type = build_nonstandard_integer_type (new_precision, true);
 
-  /* We specifically don't check here whether the target supports the
-     new operation, since it might be something that a later pattern
-     wants to rewrite anyway.  If targets have a minimum element size
-     for some optabs, we should pattern-match smaller ops to larger ops
-     where beneficial.  */
   tree new_vectype = get_vectype_for_scalar_type (vinfo, new_type);
   tree op_vectype = get_vectype_for_scalar_type (vinfo, op_type);
   if (!new_vectype || !op_vectype)
     return NULL;
 
+  /* Verify we can handle the new operation.  For shifts and rotates
+     apply heuristic of whether we are likely facing vector-vector or
+     vector-scalar operation.  Since we are eventually expecting that
+     a later pattern might eventually want to rewrite an unsupported
+     into a supported case error on that side in case the original
+     operation was not supported either or this is a binary operation
+     and the 2nd operand is constant.  */
+  if (code == RSHIFT_EXPR || code == LSHIFT_EXPR || code == RROTATE_EXPR)
+    {
+      if (!target_has_vecop_for_code (code, op_vectype, optab_vector)
+         && ((unprom[1].dt != vect_external_def
+              && unprom[1].dt != vect_constant_def)
+             || !target_has_vecop_for_code (code, op_vectype, optab_scalar))
+         && !(!target_has_vecop_for_code (code, *type_out, optab_vector)
+              && ((unprom[1].dt != vect_external_def
+                   || unprom[1].dt != vect_constant_def)
+                  || !target_has_vecop_for_code (code, *type_out,
+                                                 optab_scalar))))
+       return NULL;
+    }
+  else if (!target_has_vecop_for_code (code, op_vectype, optab_vector)
+          && (target_has_vecop_for_code (code, *type_out, optab_vector)
+              && !(nops == 2 && unprom[1].dt == vect_constant_def)))
+    return NULL;
+
   if (dump_enabled_p ())
     dump_printf_loc (MSG_NOTE, vect_location, "demoting %T to %T\n",
                     type, new_type);
@@ -4151,17 +4182,6 @@ vect_recog_vector_vector_shift_pattern (vec_info *vinfo,
   return pattern_stmt;
 }
 
-/* Return true iff the target has a vector optab implementing the operation
-   CODE on type VECTYPE.  */
-
-static bool
-target_has_vecop_for_code (tree_code code, tree vectype)
-{
-  optab voptab = optab_for_tree_code (code, vectype, optab_vector);
-  return voptab
-        && can_implement_p (voptab, TYPE_MODE (vectype));
-}
-
 /* Verify that the target has optabs of VECTYPE to perform all the steps
    needed by the multiplication-by-immediate synthesis algorithm described by
    ALG and VAR.  If SYNTH_SHIFT_P is true ensure that vector addition is