[gcc r12-2566] analyzer: Recognize __builtin_free as a matching deallocator

[gcc r12-2566] analyzer: Recognize __builtin_free as a matching deallocator

[Siddhesh Poyarekar]

https://gcc.gnu.org/g:84606efb0c6b1c1598d5ec6b05544e71596663b5

commit r12-2566-g84606efb0c6b1c1598d5ec6b05544e71596663b5
Author: Siddhesh Poyarekar <siddhesh@gotplt.org>
Date:   Wed Jul 28 10:33:46 2021 +0530

    analyzer: Recognize __builtin_free as a matching deallocator
    
    Recognize __builtin_free as being equivalent to free when passed into
    __attribute__((malloc ())), similar to how it is treated when it is
    encountered as a call.  This fixes spurious warnings in glibc where
    xmalloc family of allocators as well as reallocarray, memalign,
    etc. are declared to have __builtin_free as the free function.
    
    gcc/analyzer/ChangeLog:
    
            * sm-malloc.cc
            (malloc_state_machine::get_or_create_deallocator): Recognize
            __builtin_free.
    
    gcc/testsuite/ChangeLog:
    
            * gcc.dg/analyzer/attr-malloc-1.c (compatible_alloc,
            compatible_alloc2): New extern allocator declarations.
            (test_9, test_10): New tests.

Diff:
---
 gcc/analyzer/sm-malloc.cc                     |  3 ++-
 gcc/testsuite/gcc.dg/analyzer/attr-malloc-1.c | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/gcc/analyzer/sm-malloc.cc b/gcc/analyzer/sm-malloc.cc
index 9707a6863ce..1d69d57df0e 100644
--- a/gcc/analyzer/sm-malloc.cc
+++ b/gcc/analyzer/sm-malloc.cc
@@ -1511,7 +1511,8 @@ malloc_state_machine::get_or_create_deallocator (tree deallocator_fndecl)
   /* Reuse "free".  */
   deallocator *d;
   if (is_named_call_p (deallocator_fndecl, "free")
-      || is_std_named_call_p (deallocator_fndecl, "free"))
+      || is_std_named_call_p (deallocator_fndecl, "free")
+      || is_named_call_p (deallocator_fndecl, "__builtin_free"))
     d = &m_free.m_deallocator;
   else
     {
diff --git a/gcc/testsuite/gcc.dg/analyzer/attr-malloc-1.c b/gcc/testsuite/gcc.dg/analyzer/attr-malloc-1.c
index 3de32b1b14b..a9a2a3dee85 100644
--- a/gcc/testsuite/gcc.dg/analyzer/attr-malloc-1.c
+++ b/gcc/testsuite/gcc.dg/analyzer/attr-malloc-1.c
@@ -11,6 +11,12 @@ extern struct foo *foo_acquire (void)
 extern void use_foo (const struct foo *)
   __attribute__((nonnull));
 
+extern struct foo *compatible_alloc (void)
+  __attribute__ ((malloc (__builtin_free)));
+
+extern struct foo *compatible_alloc2 (void)
+  __attribute__ ((malloc (free)));
+
 void test_1 (void)
 {
   struct foo *p = foo_acquire ();
@@ -73,3 +79,16 @@ int test_8 (struct foo *p)
   foo_release (p);
   return p->m_int; /* { dg-warning "use after 'foo_release' of 'p'" } */
 }
+
+/* Recognize that __builtin_free and free are the same thing.  */
+void test_9 (void)
+{
+  struct foo *p = compatible_alloc ();
+  free (p);
+}
+
+void test_10 (void)
+{
+  struct foo *p = compatible_alloc2 ();
+  __builtin_free (p);
+}