[PATCH] tree-optimization/109170 - bogus use-after-free with __builtin_expect

[Richard Biener via Gcc-patches]

The following adds a missing range-op for __builtin_expect which
helps -Wuse-after-free to detect the case a realloc original
pointer is used when the result was NULL.

Bootstrap and regtest running on x86_64-unknown-linux-gnu, OK?

        PR tree-optimization/109170
        * gimple-range-op.cc (cfn_expect): New.
        (gimple_range_op_handler::maybe_builtin_call): Handle
        __builtin_expect.

        * gcc.dg/Wuse-after-free-pr109170.c: New testcase.
---
 gcc/gimple-range-op.cc                        | 25 +++++++++++++++++++
 .../gcc.dg/Wuse-after-free-pr109170.c         | 15 +++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/Wuse-after-free-pr109170.c

diff --git a/gcc/gimple-range-op.cc b/gcc/gimple-range-op.cc
index a5d625387e7..f3d6e29e58d 100644
--- a/gcc/gimple-range-op.cc
+++ b/gcc/gimple-range-op.cc
@@ -309,6 +309,25 @@ public:
   }
 } op_cfn_constant_p;
 
+// Implement range operator for integral CFN_BUILT_IN_EXPECT.
+class cfn_expect : public range_operator
+{
+public:
+  using range_operator::fold_range;
+  virtual bool fold_range (irange &r, tree, const irange &lh,
+                          const irange &, relation_trio) const
+  {
+    r = lh;
+    return true;
+  }
+  virtual bool op1_range (irange &r, tree, const irange &lhs,
+                         const irange &, relation_trio) const
+  {
+    r = lhs;
+    return true;
+  }
+} op_cfn_expect;
+
 // Implement range operator for CFN_BUILT_IN_SIGNBIT.
 class cfn_signbit : public range_operator_float
 {
@@ -966,6 +985,12 @@ gimple_range_op_handler::maybe_builtin_call ()
       m_int = &op_cfn_parity;
       break;
 
+    case CFN_BUILT_IN_EXPECT:
+      m_valid = true;
+      m_op1 = gimple_call_arg (call, 0);
+      m_int = &op_cfn_expect;
+      break;
+
     default:
       break;
     }
diff --git a/gcc/testsuite/gcc.dg/Wuse-after-free-pr109170.c 
b/gcc/testsuite/gcc.dg/Wuse-after-free-pr109170.c
new file mode 100644
index 00000000000..fa7dc66d66c
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/Wuse-after-free-pr109170.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wuse-after-free" } */
+
+unsigned long bufmax = 0;
+unsigned long __open_catalog_bufmax;
+void *realloc(void *, __SIZE_TYPE__);
+void free(void *);
+
+void __open_catalog(char *buf)
+{
+  char *old_buf = buf;
+  buf = realloc (buf, bufmax);
+  if (__builtin_expect ((buf == ((void *)0)), 0))
+    free (old_buf); /* { dg-bogus "used after" } */
+}
-- 
2.35.3