LoongArch: Fix uint64_t a & 0xfffffffffff on LA32

"uint64_t a & 0xfffffffffff" expands to two and:SI on LA32 with -O0:

(insn 8 7 9 (set (subreg:SI (reg:DI 82 [ a_2 ]) 0)
         (and:SI (reg:SI 83)
             (const_int -1 [0xffffffffffffffff]))) "t.c":3:5 -1
      (nil))
(insn 10 9 11 (set (subreg:SI (reg:DI 82 [ a_2 ]) 4)
        (and:SI (reg:SI 84)
            (const_int 4095 [0xfff]))) "t.c":3:5 -1
     (nil))

"insn 8" -1 operand can't match Yx constraint low_bitmask_len condition.

low_bitmask_len can selects a field of low-order bits within an item but not
the entire word. Add (match_test "INTVAL (op) == -1") to low_bitmask_operand
predicate.

Note: "uint64_t a & 0xffffffffffffffff" and "uint32_t a & 0xffffffff" are
optimized away before expand with -O0, can't cause this error.

gcc/ChangeLog:

	* config/loongarch/predicates.md: Add CONSTM1_RTX for low_bitmask_operand.

gcc/testsuite/ChangeLog:

	* gcc.target/loongarch/la32/and.c: New test.
	* gcc.target/loongarch/la32/la32.exp: New test.

Reviewed-by: Xi Ruoyao <xry111@xry111.site>
Reviewed-by: Lulu Cheng <chenglulu@loongson.cn>

gcc/config/loongarch/predicates.md

@@ -295,7 +295,9 @@
 
 (define_predicate "low_bitmask_operand"
   (and (match_code "const_int")
-       (match_test "low_bitmask_len (mode, INTVAL (op)) > 12")
+       (ior
+	 (match_test "low_bitmask_len (mode, INTVAL (op)) > 12")
+	 (match_test "op == CONSTM1_RTX (GET_MODE (op))"))
        (match_test "!TARGET_32BIT_R")))
 
 (define_predicate "d_operand"

gcc/testsuite/gcc.target/loongarch/la32/and.c

@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O0" } */
+
+#include <stdint.h>
+uint64_t f(uint64_t a) {
+  a = a & 0xfffffffffffff;
+  return a;
+} 

gcc/testsuite/gcc.target/loongarch/la32/la32.exp

@@ -0,0 +1,40 @@
+# Copyright (C) 2021-2025 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with GCC; see the file COPYING3.  If not see
+# <http://www.gnu.org/licenses/>.
+
+# GCC testsuite that uses the `dg.exp' driver.
+
+# Exit immediately if this isn't a LoongArch target.
+if ![istarget loongarch32*-*-*] then {
+  return
+}
+
+# Load support procs.
+load_lib gcc-dg.exp
+
+# If a testcase doesn't have special options, use these.
+global DEFAULT_CFLAGS
+if ![info exists DEFAULT_CFLAGS] then {
+    set DEFAULT_CFLAGS " "
+}
+
+# Initialize `dg'.
+dg-init
+
+# Main loop.
+dg-runtest [lsort [glob -nocomplain $srcdir/$subdir/*.\[cS\]]] \
+	"" $DEFAULT_CFLAGS
+# All done.
+dg-finish