https://bugs.gentoo.org/736685
https://gcc.gnu.org/PR96482

From 66780083a0e79e5cb7c3acc8665aa47be4084a67 Mon Sep 17 00:00:00 2001
From: Martin Liska <mliska@suse.cz>
Date: Wed, 12 Aug 2020 09:21:51 +0200
Subject: [PATCH] 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.

(cherry picked from commit d58f078ce2d53e5dab6b3d0d5f960504268e1894)
---
 gcc/ipa-cp.c                       |  3 +-
 gcc/testsuite/gcc.dg/ipa/pr96482.c | 44 ++++++++++++++++++++++++++++++
 gcc/tree-ssa-ccp.c                 |  3 ++
 3 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/ipa/pr96482.c

--- a/gcc/ipa-cp.c
+++ b/gcc/ipa-cp.c
@@ -1010,7 +1010,7 @@ ipcp_bits_lattice::set_to_constant (widest_int value, widest_int mask)
 {
   gcc_assert (top_p ());
   m_lattice_val = IPA_BITS_CONSTANT;
-  m_value = value;
+  m_value = wi::bit_and (wi::bit_not (mask), value);
   m_mask = mask;
   return true;
 }
@@ -1047,6 +1047,7 @@ ipcp_bits_lattice::meet_with_1 (widest_int value, widest_int mask,
 
   widest_int old_mask = m_mask;
   m_mask = (m_mask | mask) | (m_value ^ value);
+  m_value &= value;
 
   if (wi::sext (m_mask, precision) == -1)
     return set_to_bottom ();
--- /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;
+}
--- a/gcc/tree-ssa-ccp.c
+++ b/gcc/tree-ssa-ccp.c
@@ -306,6 +306,9 @@ get_default_value (tree var)
 		{
 		  val.lattice_val = CONSTANT;
 		  val.value = value;
+		  widest_int ipa_value = wi::to_widest (value);
+		  /* Unknown bits from IPA CP must be equal to zero.  */
+		  gcc_assert (wi::bit_and (ipa_value, mask) == 0);
 		  val.mask = mask;
 		  if (nonzero_bits != -1)
 		    val.mask &= extend_mask (nonzero_bits,
-- 
2.28.0