gimple-ssa-warn-access: Fix up asan_test.C -Wdangling-pointer regression [PR104103]

As reported in the PR or as I've seen since the weekend, asan_test.C fails
because of many warnings like:
gcc/testsuite/g++.dg/asan/asan_test.cc:1157:10: error: using a dangling pointer to an unnamed temporary [-Werror=dangling-pointer=]
gcc/testsuite/g++.dg/asan/asan_test.cc:1157:10: error: using a dangling pointer to an unnamed temporary [-Werror=dangling-pointer=]
gcc/testsuite/g++.dg/asan/asan_test.cc:1162:27: error: using a dangling pointer to an unnamed temporary [-Werror=dangling-pointer=]
...
(lots of them).
There are no dangling pointers though, the warning pass sees:
  some_automatic_var ={v} {CLOBBER};
  .ASAN_MARK (POISON, &some_automatic_var, 8);
and warns on that (both on user vars and on e.g. TARGET_EXPR temporaries).
There is nothing wrong on that, .ASAN_MARK is compiler instrumentation,
which doesn't even touch the variable in any way nor make it escaped.
What it instead does is change bytes in the shadow memory corresponding
to the variable to reflect that the variable is out of scope and make
sure that access to it would be diagnosed at runtime.
So, for all purposes of the -Wdangling-pointer and -Wuse-after-free
warnings, we should ignore this internal call.

2022-01-19  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/104103
	* gimple-ssa-warn-access.cc (pass_waccess::check_call): Don't check
	.ASAN_MARK calls.

diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index f9508a1..c36cd5d 100644 (file)
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -4234,6 +4234,11 @@ pass_waccess::check_call (gcall *stmt)
   if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
     check_builtin (stmt);
 
+  /* .ASAN_MARK doesn't access any vars, only modifies shadow memory.  */
+  if (gimple_call_internal_p (stmt)
+      && gimple_call_internal_fn (stmt) == IFN_ASAN_MARK)
+    return;
+
   if (!m_early_checks_p)
     if (tree callee = gimple_call_fndecl (stmt))
       {