Check for a supported comparison when using EXTRACT_LAST_REDUCTION

The EXTRACT_LAST_REDUCTION handling needs to generate a separate
comparison instruction that feeds the vector mask argument of the
IFN_EXTRACT_LAST call.  We weren't checking whether that comparison
was supported, leading to an ICE on the testcase.

2019-12-29  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-stmts.c (vectorizable_condition): For extract-last
	reductions, check that the target supports the required comparison
	operation.

gcc/testsuite/
	* gcc.dg/vect/vect-cond-12.c: New test.

From-SVN: r279752

gcc/ChangeLog

+2019-12-29  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* tree-vect-stmts.c (vectorizable_condition): For extract-last
+	reductions, check that the target supports the required comparison
+	operation.
+
 2019-12-27  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* config/aarch64/iterators.md (V_INT_CONTAINER): Fix VNx2SF entry.

gcc/testsuite/ChangeLog

+2019-12-29  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* gcc.dg/vect/vect-cond-12.c: New test.
+
 2019-12-27  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* gcc.target/aarch64/sve/mixed_size_11.c: New test.

gcc/testsuite/gcc.dg/vect/vect-cond-12.c

+/* { dg-do compile } */
+
+int
+f (int *x, short *y)
+{
+  int res = 100;
+  for (int i = 0; i < 40; ++i)
+    {
+      if (y[i] > 1)
+	res = x[i];
+      x[i] += y[i];
+    }
+  return res;
+}

gcc/tree-vect-stmts.c

@@ -10081,6 +10081,16 @@ vectorizable_condition (stmt_vec_info stmt_info, gimple_stmt_iterator *gsi,
       cond_code = SSA_NAME;
     }
 
+  if (TREE_CODE_CLASS (cond_code) == tcc_comparison
+      && reduction_type == EXTRACT_LAST_REDUCTION
+      && !expand_vec_cmp_expr_p (comp_vectype, vec_cmp_type, cond_code))
+    {
+      if (dump_enabled_p ())
+	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
+			 "reduction comparison operation not supported.\n");
+      return false;
+    }
+
   if (!vec_stmt)
     {
       if (bitop1 != NOP_EXPR)