[gcc/devel/c++-modules] ipa: fix bit CPP when combined with IPA bit CP

[Nathan Sidwell <nathan@gcc.gnu.org>]

https://gcc.gnu.org/g:d58f078ce2d53e5dab6b3d0d5f960504268e1894

commit d58f078ce2d53e5dab6b3d0d5f960504268e1894
Author: Martin Liska <mliska@suse.cz>
Date:   Wed Aug 12 09:21:51 2020 +0200

    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.

Diff:
---
 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(-)

diff --git a/gcc/ipa-cp.c b/gcc/ipa-cp.c
index 945a69977f3..2b21280d919 100644
--- a/gcc/ipa-cp.c
+++ b/gcc/ipa-cp.c
@@ -1011,7 +1011,7 @@ 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;
 }
@@ -1048,6 +1048,7 @@ 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 ();
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;
+}
diff --git a/gcc/tree-ssa-ccp.c b/gcc/tree-ssa-ccp.c
index 7e3921869b8..65dffe06530 100644
--- 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,