gcc/trunk/ipa-fix-bit-CPP-when-combined-with-IPA-bit-CP.patch

   1 From d58f078ce2d53e5dab6b3d0d5f960504268e1894 Mon Sep 17 00:00:00 2001
   2 From: Martin Liska <mliska@suse.cz>
   3 Date: Wed, 12 Aug 2020 09:21:51 +0200
   4 Subject: [PATCH] ipa: fix bit CPP when combined with IPA bit CP
   5
   6 As mentioned in the PR, let's consider the following example:
   7
   8 int
   9 __attribute__((noinline))
  10 foo(int arg)
  11 {
  12   if (arg == 3)
  13     return 1;
  14   if (arg == 4)
  15     return 123;
  16
  17   __builtin_unreachable ();
  18 }
  19
  20 during WPA we find all calls of the function
  21 (yes the call with value 5 is UBSAN):
  22
  23   Node: foo/0:
  24     param [0]: 5 [loc_time: 4, loc_size: 2, prop_time: 0, prop_size: 0]
  25                3 [loc_time: 3, loc_size: 3, prop_time: 0, prop_size: 0]
  26          ctxs: VARIABLE
  27          Bits: value = 0x5, mask = 0x6
  28
  29 in LTRANS we have the following VRP info:
  30
  31   # RANGE [3, 3] NONZERO 3
  32
  33 when we AND masks in get_default_value we end up with 6 & 3 = 2 (0x010).
  34 That means the only second (least significant bit) is unknown and
  35 value (5 = 0x101) & ~mask gives us either 7 (0x111) or 5 (0x101).
  36
  37 That's why if (arg_2(D) == 3) gets optimized to false.
  38
  39 gcc/ChangeLog:
  40
  41         PR ipa/96482
  42         * ipa-cp.c (ipcp_bits_lattice::meet_with_1): Drop value bits
  43         for bits that are unknown.
  44         (ipcp_bits_lattice::set_to_constant): Likewise.
  45         * tree-ssa-ccp.c (get_default_value): Add sanity check that
  46         IPA CP bit info has all bits set to zero in bits that
  47         are unknown.
  48
  49 gcc/testsuite/ChangeLog:
  50
  51         PR ipa/96482
  52         * gcc.dg/ipa/pr96482.c: New test.
  53 ---
  54  gcc/ipa-cp.c                       |  3 +-
  55  gcc/testsuite/gcc.dg/ipa/pr96482.c | 44 ++++++++++++++++++++++++++++++
  56  gcc/tree-ssa-ccp.c                 |  3 ++
  57  3 files changed, 49 insertions(+), 1 deletion(-)
  58  create mode 100644 gcc/testsuite/gcc.dg/ipa/pr96482.c
  59
  60 diff --git a/gcc/ipa-cp.c b/gcc/ipa-cp.c
  61 index 945a69977f3..2b21280d919 100644
  62 --- a/gcc/ipa-cp.c
  63 +++ b/gcc/ipa-cp.c
  64 @@ -1011,7 +1011,7 @@ ipcp_bits_lattice::set_to_constant (widest_int value, widest_int mask)
  65  {
  66    gcc_assert (top_p ());
  67    m_lattice_val = IPA_BITS_CONSTANT;
  68 -  m_value = value;
  69 +  m_value = wi::bit_and (wi::bit_not (mask), value);
  70    m_mask = mask;
  71    return true;
  72  }
  73 @@ -1048,6 +1048,7 @@ ipcp_bits_lattice::meet_with_1 (widest_int value, widest_int mask,
  74
  75    widest_int old_mask = m_mask;
  76    m_mask = (m_mask | mask) | (m_value ^ value);
  77 +  m_value &= value;
  78
  79    if (wi::sext (m_mask, precision) == -1)
  80      return set_to_bottom ();
  81 diff --git a/gcc/testsuite/gcc.dg/ipa/pr96482.c b/gcc/testsuite/gcc.dg/ipa/pr96482.c
  82 new file mode 100644
  83 index 00000000000..68ead798d28
  84 --- /dev/null
  85 +++ b/gcc/testsuite/gcc.dg/ipa/pr96482.c
  86 @@ -0,0 +1,44 @@
  87 +/* PR ipa/96482 */
  88 +/* { dg-do run } */
  89 +/* { dg-options "-O2 -flto"  } */
  90 +/* { dg-require-effective-target lto } */
  91 +
  92 +int
  93 +__attribute__((noinline))
  94 +foo(int arg)
  95 +{
  96 +  if (arg == 3)
  97 +    return 1;
  98 +  if (arg == 4)
  99 +    return 123;
 100 +
 101 +  __builtin_unreachable ();
 102 +}
 103 +
 104 +int
 105 +__attribute__((noinline))
 106 +baz(int x)
 107 +{
 108 +  if (x != 0)
 109 +    return foo(3); /* called */
 110 +
 111 +  return 1;
 112 +}
 113 +
 114 +int
 115 +__attribute__((noinline))
 116 +bar(int x)
 117 +{
 118 +  if (x == 0)
 119 +    return foo(5); /* not executed */
 120 +
 121 +  return 1;
 122 +}
 123 +
 124 +int main(int argc, char **argv)
 125 +{
 126 +  if (bar(argc) != baz(argc))
 127 +    __builtin_abort ();
 128 +
 129 +  return 0;
 130 +}
 131 diff --git a/gcc/tree-ssa-ccp.c b/gcc/tree-ssa-ccp.c
 132 index 7e3921869b8..65dffe06530 100644
 133 --- a/gcc/tree-ssa-ccp.c
 134 +++ b/gcc/tree-ssa-ccp.c
 135 @@ -306,6 +306,9 @@ get_default_value (tree var)
 136                 {
 137                   val.lattice_val = CONSTANT;
 138                   val.value = value;
 139 +                 widest_int ipa_value = wi::to_widest (value);
 140 +                 /* Unknown bits from IPA CP must be equal to zero.  */
 141 +                 gcc_assert (wi::bit_and (ipa_value, mask) == 0);
 142                   val.mask = mask;
 143                   if (nonzero_bits != -1)
 144                     val.mask &= extend_mask (nonzero_bits,
 145 --
 146 2.28.0
 147