analyzer: don't warn for deref-before-check for checks in macros [PR108745]

Integration testing shows this patch fixes all 9 known false positives
from -Wanalyzer-deref-before-check within ImageMagick-7.1.0-57, and
eliminates 34 further as-yet unassessed such diagnostics, without
eliminating the 1 known true positive.

This improves the rate of true positives for the warning from
1.56% to 4.76% of the total:

-Wanalyzer-deref-before-check: 1.56% -> 4.76% (GOOD: 1 BAD: 63->20)
    TRUE:  1
   FALSE: 15 ->  6 (-9)
             ImageMagick-7.1.0-57:  9 ->  0 (-9)
    TODO: 48 -> 14 (-34)
             ImageMagick-7.1.0-57: 21 ->  1 (-20)
                       qemu-7.2.0: 25 -> 11 (-14)

gcc/analyzer/ChangeLog:
	PR analyzer/108745
	* sm-malloc.cc (deref_before_check::emit): Reject the warning if
	the check occurs within a macro defintion.

gcc/testsuite/ChangeLog:
	PR analyzer/108745
	* gcc.dg/analyzer/deref-before-check-macro-pr108745.c: New test.
	* gcc.dg/analyzer/deref-before-check-macro.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>

1 files changed, 37 insertions, 0 deletions

diff --git a/gcc/analyzer/sm-malloc.cc b/gcc/analyzer/sm-malloc.cc
index 9aee810..c24fe73 100644
--- a/gcc/analyzer/sm-malloc.cc
+++ b/gcc/analyzer/sm-malloc.cc
@@ -1519,6 +1519,43 @@ public:
 	!= &m_check_enode->get_point ().get_call_string ())
       return false;
 
+    /* Reject the warning if the check occurs within a macro defintion.
+       This avoids false positives for such code as:
+
+	#define throw_error \
+	   do {             \
+	     if (p)         \
+	       cleanup (p); \
+	     return;        \
+	   } while (0)
+
+	if (p->idx >= n)
+	  throw_error ();
+
+       where the usage of "throw_error" implicitly adds a check
+       on 'p'.
+
+       We do warn when the check is in a macro expansion if we can get
+       at the location of the condition and it is't part of the
+       definition, so that we warn for checks such as:
+	   if (words[0][0] == '@')
+	     return;
+	   g_assert(words[0] != NULL); <--- here
+       Unfortunately we don't have locations for individual gimple
+       arguments, so in:
+	   g_assert (ptr);
+       we merely have a gimple_cond
+	   if (p_2(D) == 0B)
+       with no way of getting at the location of the condition separately
+       from that of the gimple_cond (where the "if" is within the macro
+       definition).  We reject the warning for such cases.
+
+       We do warn when the *deref* occurs in a macro, since this can be
+       a source of real bugs; see e.g. PR 77425.  */
+    location_t check_loc = m_check_enode->get_point ().get_location ();
+    if (linemap_location_from_macro_definition_p (line_table, check_loc))
+      return false;
+
     /* Reject the warning if the deref's BB doesn't dominate that
        of the check, so that we don't warn e.g. for shared cleanup
        code that checks a pointer for NULL, when that code is sometimes