[RFC] Add support for vectors in comparisons (like the C++ frontend does)

[Paul Iannetta <piannetta@kalrayinc.com>]

Hi,

I am trying to bridge the gap between the extensions supported by the C
and C++ front-ends.  When it comes to vector extensions, C++ supports
vectors in comparisons and within conditional expressions whereas the C
front-end does not.

I have a patch to bring this feature to the C front-end as well, and
would like to hear your opinion on it, especially since it may affect
the feature-set of the objc front-end as well.

I have tried to mirror as much as possible what the C++ front-end does
and checked that both front-end produce the same GIMPLE for all the
simple expressions as well as some more complex combinations of the
operators (?:, !, ^, || and &&).

Currently, this is only a tentative patch and I did not add any tests
to the testsuite.  Moreover, the aarch64's target-specific testsuite
explicitly tests the non-presence of this feature, which will have to
be removed.

I've run the testsuite on x86 and I've not seen any regressions.

Cheers,
Paul

# ------------------------ >8 ------------------------
Support for vector types in simple comparisons

gcc/

	* doc/extend.texi: Remove the C++ mention, since both C and C++
	  support the all the mentioned features.

gcc/c/

	* c-typeck.cc (build_unary_op): Add support for vector for the
	  unary exclamation mark.
	(build_conditional_expr): Add support for vector in conditional
	expressions.
	(build_binary_op): Add support for vector for &&, || and ^.
	(c_objc_common_truthvalue_conversion): Remove the special gards
	preventing vector types.

# ------------------------ >8 ------------------------
diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 17185fd3da4..03ade14cae9 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -4536,12 +4536,15 @@ build_unary_op (location_t location, enum tree_code code, tree xarg,
     case TRUTH_NOT_EXPR:
       if (typecode != INTEGER_TYPE && typecode != FIXED_POINT_TYPE
 	  && typecode != REAL_TYPE && typecode != POINTER_TYPE
-	  && typecode != COMPLEX_TYPE)
+	  && typecode != COMPLEX_TYPE && typecode != VECTOR_TYPE)
 	{
 	  error_at (location,
 		    "wrong type argument to unary exclamation mark");
 	  return error_mark_node;
 	}
+      if (gnu_vector_type_p (TREE_TYPE (arg)))
+	return build_binary_op (location, EQ_EXPR, arg,
+				build_zero_cst (TREE_TYPE (arg)), false);
       if (int_operands)
 	{
 	  arg = c_objc_common_truthvalue_conversion (location, xarg);
@@ -5477,6 +5480,129 @@ build_conditional_expr (location_t colon_loc, tree ifexp, bool ifexp_bcp,
       result_type = type2;
     }
 
+  if (gnu_vector_type_p (TREE_TYPE (ifexp))
+      && VECTOR_INTEGER_TYPE_P (TREE_TYPE (ifexp)))
+    {
+      tree ifexp_type = TREE_TYPE (ifexp);
+
+      /* If ifexp is another cond_expr choosing between -1 and 0,
+	 then we can use its comparison.  It may help to avoid
+	 additional comparison, produce more accurate diagnostics
+	 and enables folding.  */
+      if (TREE_CODE (ifexp) == VEC_COND_EXPR
+	  && integer_minus_onep (TREE_OPERAND (ifexp, 1))
+	  && integer_zerop (TREE_OPERAND (ifexp, 2)))
+	ifexp = TREE_OPERAND (ifexp, 0);
+
+      tree op1_type = TREE_TYPE (op1);
+      tree op2_type = TREE_TYPE (op2);
+
+      if (!VECTOR_TYPE_P (op1_type) && !VECTOR_TYPE_P (op2_type))
+	{
+	  /* Rely on the error messages of the scalar version.  */
+	  tree scal =
+	    build_conditional_expr (colon_loc, integer_one_node, ifexp_bcp,
+				    op1, op1_original_type, op1_loc,
+				    op2, op2_original_type, op2_loc);
+	  if (scal == error_mark_node)
+	    return error_mark_node;
+	  tree stype = TREE_TYPE (scal);
+	  tree ctype = TREE_TYPE (ifexp_type);
+	  if (TYPE_SIZE (stype) != TYPE_SIZE (ctype)
+	      || (!INTEGRAL_TYPE_P (stype) && !SCALAR_FLOAT_TYPE_P (stype)))
+	    {
+	      error_at (colon_loc,
+			"inferred scalar type %qT is not an integer or "
+			"floating-point type of the same size as %qT", stype,
+			COMPARISON_CLASS_P (ifexp)
+			? TREE_TYPE (TREE_TYPE (TREE_OPERAND (ifexp, 0)))
+			: ctype);
+	      return error_mark_node;
+	    }
+
+	  tree vtype = build_opaque_vector_type (stype,
+						 TYPE_VECTOR_SUBPARTS
+						 (ifexp_type));
+	  /* The warnings (like Wsign-conversion) have already been
+	     given by the scalar build_conditional_expr. We still check
+	     unsafe_conversion_p to forbid truncating long long -> float.  */
+	  if (unsafe_conversion_p (stype, op1, NULL_TREE, false))
+	    {
+	      error_at (colon_loc, "conversion of scalar %qT to vector %qT "
+			"involves truncation", op1_type, vtype);
+	      return error_mark_node;
+	    }
+	  if (unsafe_conversion_p (stype, op2, NULL_TREE, false))
+	    {
+	      error_at (colon_loc, "conversion of scalar %qT to vector %qT "
+			"involves truncation", op2_type, vtype);
+	      return error_mark_node;
+	    }
+
+	  op1 = convert (stype, op1);
+	  op1 = save_expr (op1);
+	  op1 = build_vector_from_val (vtype, op1);
+	  op1_type = vtype;
+	  op2 = convert (stype, op2);
+	  op2 = save_expr (op2);
+	  op2 = build_vector_from_val (vtype, op2);
+	  op2_type = vtype;
+	}
+
+      if (gnu_vector_type_p (op1_type) ^ gnu_vector_type_p (op2_type))
+	{
+	  enum stv_conv convert_flag =
+	    scalar_to_vector (colon_loc, VEC_COND_EXPR, op1, op2,
+			      true);
+
+	  switch (convert_flag)
+	    {
+	    case stv_error:
+	      return error_mark_node;
+	    case stv_firstarg:
+	      {
+		op1 = save_expr (op1);
+		op1 = convert (TREE_TYPE (op2_type), op1);
+		op1 = build_vector_from_val (op2_type, op1);
+		op1_type = TREE_TYPE (op1);
+		break;
+	      }
+	    case stv_secondarg:
+	      {
+		op2 = save_expr (op2);
+		op2 = convert (TREE_TYPE (op1_type), op2);
+		op2 = build_vector_from_val (op1_type, op2);
+		op2_type = TREE_TYPE (op2);
+		break;
+	      }
+	    default:
+	      break;
+	    }
+	}
+
+      if (!gnu_vector_type_p (op1_type)
+	  || !gnu_vector_type_p (op2_type)
+	  || !comptypes (op1_type, op2_type)
+	  || maybe_ne (TYPE_VECTOR_SUBPARTS (ifexp_type),
+		       TYPE_VECTOR_SUBPARTS (op1_type))
+	  || TYPE_SIZE (ifexp_type) != TYPE_SIZE (op1_type))
+	{
+	  error_at (colon_loc,
+		    "incompatible vector types in conditional expression: "
+		    "%qT, %qT and %qT", TREE_TYPE (ifexp),
+		    TREE_TYPE (orig_op1), TREE_TYPE (orig_op2));
+	  return error_mark_node;
+	}
+
+      if (!COMPARISON_CLASS_P (ifexp))
+	{
+	  tree cmp_type = truth_type_for (ifexp_type);
+	  ifexp = build2 (NE_EXPR, cmp_type, ifexp,
+			  build_zero_cst (ifexp_type));
+	}
+      return build3_loc (colon_loc, VEC_COND_EXPR, op1_type, ifexp, op1, op2);
+    }
+
   if (!result_type)
     {
       if (flag_cond_mismatch)
@@ -5522,17 +5648,6 @@ build_conditional_expr (location_t colon_loc, tree ifexp, bool ifexp_bcp,
 		       && !TREE_OVERFLOW (orig_op2)));
     }
 
-  /* Need to convert condition operand into a vector mask.  */
-  if (VECTOR_TYPE_P (TREE_TYPE (ifexp)))
-    {
-      tree vectype = TREE_TYPE (ifexp);
-      tree elem_type = TREE_TYPE (vectype);
-      tree zero = build_int_cst (elem_type, 0);
-      tree zero_vec = build_vector_from_val (vectype, zero);
-      tree cmp_type = truth_type_for (vectype);
-      ifexp = build2 (NE_EXPR, cmp_type, ifexp, zero_vec);
-    }
-
   if (int_const || (ifexp_bcp && TREE_CODE (ifexp) == INTEGER_CST))
     ret = fold_build3_loc (colon_loc, COND_EXPR, result_type, ifexp, op1, op2);
   else
@@ -12105,6 +12220,54 @@ build_binary_op (location_t location, enum tree_code code,
 		       && (op0 == truthvalue_true_node
 			   || !TREE_OVERFLOW (orig_op1)));
 	}
+      if (!VECTOR_TYPE_P (type0) && gnu_vector_type_p (type1))
+	{
+	  if (!COMPARISON_CLASS_P (op1))
+	    op1 = build_binary_op (EXPR_LOCATION (op1), NE_EXPR, op1,
+				   build_zero_cst (type1), false);
+	  if (code == TRUTH_ANDIF_EXPR)
+	    {
+	      tree z = build_zero_cst (TREE_TYPE (op1));
+	      return build_conditional_expr (location, op0, 0,
+					     op1, NULL_TREE, EXPR_LOCATION (op1),
+					     z, NULL_TREE, EXPR_LOCATION (z));
+	    }
+	  else if (code == TRUTH_ORIF_EXPR)
+	    {
+	      tree m1 = build_all_ones_cst (TREE_TYPE (op1));
+	      return build_conditional_expr (location, op0, 0,
+					      m1, NULL_TREE, EXPR_LOCATION (m1),
+					      op1, NULL_TREE, EXPR_LOCATION (op1));
+	    }
+	  else
+	    gcc_unreachable ();
+	}
+      if (gnu_vector_type_p (type0)
+	  && (!VECTOR_TYPE_P (type1) || gnu_vector_type_p (type1)))
+	{
+	  if (!COMPARISON_CLASS_P (op0))
+	    op0 = build_binary_op (EXPR_LOCATION (op0), NE_EXPR, op0,
+				      build_zero_cst (type0), false);
+	  if (!VECTOR_TYPE_P (type1))
+	    {
+	      tree m1 = build_all_ones_cst (TREE_TYPE (op0));
+	      tree z = build_zero_cst (TREE_TYPE (op0));
+	      op1 = build_conditional_expr (location, op1, 0,
+					    m1, NULL_TREE, EXPR_LOCATION (m1),
+					    z, NULL_TREE, EXPR_LOCATION(z));
+	    }
+	  else if (!COMPARISON_CLASS_P (op1))
+	    op1 = build_binary_op (EXPR_LOCATION (op1), NE_EXPR, op1,
+				   build_zero_cst (type1), false);
+	  if (code == TRUTH_ANDIF_EXPR)
+	    code = BIT_AND_EXPR;
+	  else if (code == TRUTH_ORIF_EXPR)
+	    code = BIT_IOR_EXPR;
+	  else
+	    gcc_unreachable ();
+
+	  return build_binary_op (location, code, op0, op1, false);
+	}
       break;
 
       /* Shift operations: result has same type as first operand;
@@ -12906,10 +13069,6 @@ c_objc_common_truthvalue_conversion (location_t location, tree expr)
     case FUNCTION_TYPE:
       gcc_unreachable ();
 
-    case VECTOR_TYPE:
-      error_at (location, "used vector type where scalar is required");
-      return error_mark_node;
-
     default:
       break;
     }
@@ -12924,8 +13083,6 @@ c_objc_common_truthvalue_conversion (location_t location, tree expr)
       expr = note_integer_operands (expr);
     }
   else
-    /* ??? Should we also give an error for vectors rather than leaving
-       those to give errors later?  */
     expr = c_common_truthvalue_conversion (location, expr);
 
   if (TREE_CODE (expr) == INTEGER_CST && int_operands && !int_const)
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index c89df8778b2..1e0d436c02c 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -12007,7 +12007,7 @@ c = a >  b;     /* The result would be @{0, 0,-1, 0@}  */
 c = a == b;     /* The result would be @{0,-1, 0,-1@}  */
 @end smallexample
 
-In C++, the ternary operator @code{?:} is available. @code{a?b:c}, where
+The ternary operator @code{?:} is available. @code{a?b:c}, where
 @code{b} and @code{c} are vectors of the same type and @code{a} is an
 integer vector with the same number of elements of the same size as @code{b}
 and @code{c}, computes all three arguments and creates a vector
@@ -12020,7 +12020,7 @@ vector. If both @code{b} and @code{c} are scalars and the type of
 @code{b} and @code{c} are converted to a vector type whose elements have
 this type and with the same number of elements as @code{a}.
 
-In C++, the logic operators @code{!, &&, ||} are available for vectors.
+The logic operators @code{!, &&, ||} are available for vectors.
 @code{!v} is equivalent to @code{v == 0}, @code{a && b} is equivalent to
 @code{a!=0 & b!=0} and @code{a || b} is equivalent to @code{a!=0 | b!=0}.
 For mixed operations between a scalar @code{s} and a vector @code{v},