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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
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