vect: while_ult for integer masks

Add a vector length parameter needed by amdgcn without breaking aarch64.

All amdgcn vector masks are DImode, regardless of vector length, so we can't
tell what length is implied simply from the operator mode.  (Even if we used
different integer modes there's no mode small enough to differenciate a 2 or
4 lane mask).  Without knowing the intended length we end up using a mask with
too many lanes enabled, which leads to undefined behaviour..

The extra operand is not added for vector mask types so AArch64 does not need
to be adjusted.

gcc/ChangeLog:

	* config/gcn/gcn-valu.md (while_ultsidi): Limit mask length using
	operand 3.
	* doc/md.texi (while_ult): Document new operand 3 usage.
	* internal-fn.cc (expand_while_optab_fn): Set operand 3 when lhs_type
	maps to a non-vector mode.

diff --git a/gcc/config/gcn/gcn-valu.md b/gcc/config/gcn/gcn-valu.md
index 3bfdf8213fc..dec81e863f7 100644
--- a/gcc/config/gcn/gcn-valu.md
+++ b/gcc/config/gcn/gcn-valu.md
@@ -3052,7 +3052,8 @@ (define_expand "vcondu<V_ALL:mode><V_INT:mode>_exec"
 (define_expand "while_ultsidi"
   [(match_operand:DI 0 "register_operand")
    (match_operand:SI 1 "")
-   (match_operand:SI 2 "")]
+   (match_operand:SI 2 "")
+   (match_operand:SI 3 "")]
   ""
   {
     if (GET_CODE (operands[1]) != CONST_INT
@@ -3077,6 +3078,11 @@ (define_expand "while_ultsidi"
 			      : ~((unsigned HOST_WIDE_INT)-1 << diff));
 	emit_move_insn (operands[0], gen_rtx_CONST_INT (VOIDmode, mask));
       }
+    if (INTVAL (operands[3]) < 64)
+      emit_insn (gen_anddi3 (operands[0], operands[0],
+			     gen_rtx_CONST_INT (VOIDmode,
+						~((unsigned HOST_WIDE_INT)-1
+						  << INTVAL (operands[3])))));
     DONE;
   })
 
diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index d46963f468c..bb42ee1da36 100644
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -4950,9 +4950,10 @@ This pattern is not allowed to @code{FAIL}.
 @cindex @code{while_ult@var{m}@var{n}} instruction pattern
 @item @code{while_ult@var{m}@var{n}}
 Set operand 0 to a mask that is true while incrementing operand 1
-gives a value that is less than operand 2.  Operand 0 has mode @var{n}
-and operands 1 and 2 are scalar integers of mode @var{m}.
-The operation is equivalent to:
+gives a value that is less than operand 2, for a vector length up to operand 3.
+Operand 0 has mode @var{n} and operands 1 and 2 are scalar integers of mode
+@var{m}.  Operand 3 should be omitted when @var{n} is a vector mode, and
+a @code{CONST_INT} otherwise.  The operation for vector modes is equivalent to:
 
 @smallexample
 operand0[0] = operand1 < operand2;
@@ -4960,6 +4961,14 @@ for (i = 1; i < GET_MODE_NUNITS (@var{n}); i++)
   operand0[i] = operand0[i - 1] && (operand1 + i < operand2);
 @end smallexample
 
+And for non-vector modes the operation is equivalent to:
+
+@smallexample
+operand0[0] = operand1 < operand2;
+for (i = 1; i < operand3; i++)
+  operand0[i] = operand0[i - 1] && (operand1 + i < operand2);
+@end smallexample
+
 @cindex @code{check_raw_ptrs@var{m}} instruction pattern
 @item @samp{check_raw_ptrs@var{m}}
 Check whether, given two pointers @var{a} and @var{b} and a length @var{len},
diff --git a/gcc/internal-fn.cc b/gcc/internal-fn.cc
index 651d99eaeb9..c306240c2ac 100644
--- a/gcc/internal-fn.cc
+++ b/gcc/internal-fn.cc
@@ -3664,7 +3664,7 @@ expand_direct_optab_fn (internal_fn fn, gcall *stmt, direct_optab optab,
 static void
 expand_while_optab_fn (internal_fn, gcall *stmt, convert_optab optab)
 {
-  expand_operand ops[3];
+  expand_operand ops[4];
   tree rhs_type[2];
 
   tree lhs = gimple_call_lhs (stmt);
@@ -3680,10 +3680,24 @@ expand_while_optab_fn (internal_fn, gcall *stmt, convert_optab optab)
       create_input_operand (&ops[i + 1], rhs_rtx, TYPE_MODE (rhs_type[i]));
     }
 
+  int opcnt;
+  if (!VECTOR_MODE_P (TYPE_MODE (lhs_type)))
+    {
+      /* When the mask is an integer mode the exact vector length may not
+	 be clear to the backend, so we pass it in operand[3].
+         Use the vector in arg2 for the most reliable intended size.  */
+      tree type = TREE_TYPE (gimple_call_arg (stmt, 2));
+      create_integer_operand (&ops[3], TYPE_VECTOR_SUBPARTS (type));
+      opcnt = 4;
+    }
+  else
+    /* The mask has a vector type so the length operand is unnecessary.  */
+    opcnt = 3;
+
   insn_code icode = convert_optab_handler (optab, TYPE_MODE (rhs_type[0]),
 					   TYPE_MODE (lhs_type));
 
-  expand_insn (icode, 3, ops);
+  expand_insn (icode, opcnt, ops);
   if (!rtx_equal_p (lhs_rtx, ops[0].value))
     emit_move_insn (lhs_rtx, ops[0].value);
 }