ipa: fix bit CPP when combined with IPA bit CP

As mentioned in the PR, let's consider the following example:

int
__attribute__((noinline))
foo(int arg)
{
  if (arg == 3)
    return 1;
  if (arg == 4)
    return 123;

  __builtin_unreachable ();
}

during WPA we find all calls of the function
(yes the call with value 5 is UBSAN):

  Node: foo/0:
    param [0]: 5 [loc_time: 4, loc_size: 2, prop_time: 0, prop_size: 0]
               3 [loc_time: 3, loc_size: 3, prop_time: 0, prop_size: 0]
         ctxs: VARIABLE
         Bits: value = 0x5, mask = 0x6

in LTRANS we have the following VRP info:

  # RANGE [3, 3] NONZERO 3

when we AND masks in get_default_value we end up with 6 & 3 = 2 (0x010).
That means the only second (least significant bit) is unknown and
value (5 = 0x101) & ~mask gives us either 7 (0x111) or 5 (0x101).

That's why if (arg_2(D) == 3) gets optimized to false.

gcc/ChangeLog:

	PR ipa/96482
	* ipa-cp.c (ipcp_bits_lattice::meet_with_1): Drop value bits
	for bits that are unknown.
	(ipcp_bits_lattice::set_to_constant): Likewise.
	* tree-ssa-ccp.c (get_default_value): Add sanity check that
	IPA CP bit info has all bits set to zero in bits that
	are unknown.

gcc/testsuite/ChangeLog:

	PR ipa/96482
	* gcc.dg/ipa/pr96482.c: New test.

1 files changed, 44 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/ipa/pr96482.c b/gcc/testsuite/gcc.dg/ipa/pr96482.c
new file mode 100644
index 00000000000..68ead798d28
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/pr96482.c
@@ -0,0 +1,44 @@
+/* PR ipa/96482 */
+/* { dg-do run } */
+/* { dg-options "-O2 -flto"  } */
+/* { dg-require-effective-target lto } */
+
+int
+__attribute__((noinline))
+foo(int arg)
+{
+  if (arg == 3)
+    return 1;
+  if (arg == 4)
+    return 123;
+
+  __builtin_unreachable ();
+}
+
+int
+__attribute__((noinline))
+baz(int x)
+{
+  if (x != 0)
+    return foo(3); /* called */
+
+  return 1;
+}
+
+int
+__attribute__((noinline))
+bar(int x)
+{
+  if (x == 0)
+    return foo(5); /* not executed */
+
+  return 1;
+}
+
+int main(int argc, char **argv)
+{
+  if (bar(argc) != baz(argc))
+    __builtin_abort ();
+
+  return 0;
+}