[gcc r12-783] Avoid -Wuninitialized false negatives with sanitization and VLAs.

[Martin Sebor <msebor@gcc.gnu.org>]

https://gcc.gnu.org/g:2efe245bb88bf4574e322ef7e6d2df83d9e13237

commit r12-783-g2efe245bb88bf4574e322ef7e6d2df83d9e13237
Author: Martin Sebor <msebor@redhat.com>
Date:   Thu May 13 16:05:50 2021 -0600

    Avoid -Wuninitialized false negatives with sanitization and VLAs.
    
    Resolves:
    PR tree-optimization/93100 - gcc -fsanitize=address inhibits -Wuninitialized
    PR middle-end/98583 - missing -Wuninitialized reading from a second VLA in its own block
    
    gcc/ChangeLog:
    
            PR tree-optimization/93100
            PR middle-end/98583
            * tree-ssa-uninit.c (check_defs): Exclude intrinsic functions that
            don't modify referenced objects.
    
    gcc/testsuite/ChangeLog:
    
            PR tree-optimization/93100
            PR middle-end/98583
            * g++.dg/warn/uninit-pr93100.C: New test.
            * gcc.dg/uninit-pr93100.c: New test.
            * gcc.dg/uninit-pr98583.c: New test.

Diff:
---
 gcc/testsuite/g++.dg/warn/uninit-pr93100.C | 59 ++++++++++++++++++++++++
 gcc/testsuite/gcc.dg/uninit-pr93100.c      | 74 ++++++++++++++++++++++++++++++
 gcc/testsuite/gcc.dg/uninit-pr98583.c      | 31 +++++++++++++
 gcc/tree-ssa-uninit.c                      | 11 +++++
 4 files changed, 175 insertions(+)

diff --git a/gcc/testsuite/g++.dg/warn/uninit-pr93100.C b/gcc/testsuite/g++.dg/warn/uninit-pr93100.C
new file mode 100644
index 00000000000..c9cd3ef0174
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/uninit-pr93100.C
@@ -0,0 +1,59 @@
+/* PR tree-optimization/98508 - Sanitizer disable -Wall and -Wextra
+   { dg-do compile }
+   { dg-options "-O0 -Wall -fsanitize=address" } */
+
+struct S
+{
+  int a;
+};
+
+void warn_init_self_O0 ()
+{
+  S s = S (s);      // { dg-warning "\\\[-Wuninitialized" }
+  (void)&s;
+}
+
+
+void warn_init_self_use_O0 ()
+{
+  S s = S (s);      // { dg-warning "\\\[-Wuninitialized" }
+
+  void sink (void*);
+  sink (&s);
+}
+
+
+#pragma GCC optimize ("1")
+
+void warn_init_self_O1 ()
+{
+  S s = S (s);      // { dg-warning "\\\[-Wuninitialized" }
+  (void)&s;
+}
+
+
+void warn_init_self_use_O1 ()
+{
+  S s = S (s);      // { dg-warning "\\\[-Wuninitialized" }
+
+  void sink (void*);
+  sink (&s);
+}
+
+
+#pragma GCC optimize ("2")
+
+void warn_init_self_O2 ()
+{
+  S s = S (s);      // { dg-warning "\\\[-Wuninitialized" }
+  (void)&s;
+}
+
+
+void warn_init_self_use_O2 ()
+{
+  S s = S (s);      // { dg-warning "\\\[-Wuninitialized" }
+
+  void sink (void*);
+  sink (&s);
+}
diff --git a/gcc/testsuite/gcc.dg/uninit-pr93100.c b/gcc/testsuite/gcc.dg/uninit-pr93100.c
new file mode 100644
index 00000000000..61b7e434038
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/uninit-pr93100.c
@@ -0,0 +1,74 @@
+/* PR tree-optimization/93100 - gcc -fsanitize=address inhibits -Wuninitialized
+   { dg-do compile }
+   { dg-options "-Wall -fsanitize=address" } */
+
+struct A
+{
+  _Bool b;
+  int i;
+};
+
+void warn_A_b_O0 (void)
+{
+  struct A a;
+
+  if (a.b)          // { dg-warning "\\\[-Wuninitialized" }
+    {
+      (void)&a;
+    }
+}
+
+void warn_A_i_O0 (void)
+{
+  struct A a;
+
+  if (a.i)          // { dg-warning "\\\[-Wuninitialized" }
+    {
+      (void)&a;
+    }
+}
+
+#pragma GCC optimize ("1")
+
+void warn_A_b_O1 (void)
+{
+  struct A a;
+
+  if (a.b)          // { dg-warning "\\\[-Wuninitialized" }
+    {
+      (void)&a;
+    }
+}
+
+void warn_A_i_O1 (void)
+{
+  struct A a;
+
+  if (a.i)          // { dg-warning "\\\[-Wuninitialized" }
+    {
+      (void)&a;
+    }
+}
+
+
+#pragma GCC optimize ("2")
+
+void warn_A_b_O2 (void)
+{
+  struct A a;
+
+  if (a.b)          // { dg-warning "\\\[-Wuninitialized" }
+    {
+      (void)&a;
+    }
+}
+
+void warn_A_i_O2 (void)
+{
+  struct A a;
+
+  if (a.i)          // { dg-warning "\\\[-Wuninitialized" }
+    {
+      (void)&a;
+    }
+}
diff --git a/gcc/testsuite/gcc.dg/uninit-pr98583.c b/gcc/testsuite/gcc.dg/uninit-pr98583.c
new file mode 100644
index 00000000000..638b0295809
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/uninit-pr98583.c
@@ -0,0 +1,31 @@
+/* PR middle-end/98583 - missing -Wuninitialized reading from a second VLA
+   in its own block
+   { dg-do compile }
+   { dg-options "-O2 -Wall" } */
+
+void f (int*);
+void g (int);
+
+void h1 (int n)
+{
+  int a[n];
+  f (a);
+
+  int b[n];
+  g (b[1]);         // { dg-warning "\\\[-Wuninitialized" }
+}
+
+void h2 (int n, int i, int j)
+{
+  if (i)
+    {
+      int a[n];
+      f (a);
+    }
+
+  if (j)
+    {
+      int b[n];
+      g (b[1]);     // { dg-warning "\\\[-Wmaybe-uninitialized" }
+    }
+}
diff --git a/gcc/tree-ssa-uninit.c b/gcc/tree-ssa-uninit.c
index 0800f596ab1..f55ce1939ac 100644
--- a/gcc/tree-ssa-uninit.c
+++ b/gcc/tree-ssa-uninit.c
@@ -209,6 +209,16 @@ check_defs (ao_ref *ref, tree vdef, void *data_)
 {
   check_defs_data *data = (check_defs_data *)data_;
   gimple *def_stmt = SSA_NAME_DEF_STMT (vdef);
+
+  /* The ASAN_MARK intrinsic doesn't modify the variable.  */
+  if (is_gimple_call (def_stmt)
+      && gimple_call_internal_p (def_stmt, IFN_ASAN_MARK))
+    return false;
+
+  /* End of VLA scope is not a kill.  */
+  if (gimple_call_builtin_p (def_stmt, BUILT_IN_STACK_RESTORE))
+    return false;
+
   /* If this is a clobber then if it is not a kill walk past it.  */
   if (gimple_clobber_p (def_stmt))
     {
@@ -216,6 +226,7 @@ check_defs (ao_ref *ref, tree vdef, void *data_)
 	return true;
       return false;
     }
+
   /* Found a may-def on this path.  */
   data->found_may_defs = true;
   return true;