[PATCH v2] C++: Fix crash in warn_for_memset within templates (PR c++/83814)

[David Malcolm <dmalcolm at redhat dot com>]

On Wed, 2018-01-17 at 09:28 -0500, Jason Merrill wrote:
> On Wed, Jan 17, 2018 at 5:34 AM, Jakub Jelinek <jakub@redhat.com>
> wrote:
> > On Fri, Jan 12, 2018 at 05:09:24PM -0500, David Malcolm wrote:
> > > PR c++/83814 reports an ICE introduced by the location wrapper
> > > patch
> > > (r256448), affecting certain memset calls within templates.
> > 
> > Note, I think this issue sadly affects a lot of code, so it is
> > quite urgent.
> > 
> > That said, wonder if we really can't do any folding when
> > processing_template_decl, could we e.g. do at least
> > maybe_constant_value,
> > or fold if the expression is not type nor value dependent?
> 
> Yes, in a template we should call fold_non_dependent_expr.
> 
> > BTW, never know if cp_fold_rvalue is a superset of
> > maybe_constant_value or not.
> 
> It is.
> 
> Jason

Thanks.  Here's an updated version of the patch.

Changed in v2:
* use fold_non_dependent_expr in the C++ impl of fold_for_warn
* add some test coverage of folding to g++.dg/wrappers/pr83814.C
* added another testcase (from PR c++/83902)

Successfully bootstrapped&regrtested on x86_64-pc-linux-gnu.
OK for trunk?


gcc/c-family/ChangeLog:
	PR c++/83814
	* c-common.c (fold_for_warn): Move to c/c-fold.c and cp/expr.c.

gcc/c/ChangeLog:
	PR c++/83814
	* c-fold.c (fold_for_warn): Move from c-common.c, reducing to just
	the C part.

gcc/cp/ChangeLog:
	PR c++/83814
	* expr.c (fold_for_warn): Move from c-common.c, reducing to just
	the C++ part.  If processing a template, call
	fold_non_dependent_expr rather than fully folding.

gcc/testsuite/ChangeLog:
	PR c++/83814
	PR c++/83902
	* g++.dg/wrappers/pr83814.C: New test case.
	* g++.dg/wrappers/pr83902.C: New test case.
---
 gcc/c-family/c-common.c                 | 13 ------
 gcc/c/c-fold.c                          | 10 +++++
 gcc/cp/expr.c                           | 15 +++++++
 gcc/testsuite/g++.dg/wrappers/pr83814.C | 70 +++++++++++++++++++++++++++++++++
 gcc/testsuite/g++.dg/wrappers/pr83902.C |  9 +++++
 5 files changed, 104 insertions(+), 13 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/wrappers/pr83814.C
 create mode 100644 gcc/testsuite/g++.dg/wrappers/pr83902.C

diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 097d192..858ed68 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -868,19 +868,6 @@ c_get_substring_location (const substring_loc &substr_loc,
 }
 
 
-/* Fold X for consideration by one of the warning functions when checking
-   whether an expression has a constant value.  */
-
-tree
-fold_for_warn (tree x)
-{
-  if (c_dialect_cxx ())
-    return c_fully_fold (x, /*for_init*/false, /*maybe_constp*/NULL);
-  else
-    /* The C front-end has already folded X appropriately.  */
-    return x;
-}
-
 /* Return true iff T is a boolean promoted to int.  */
 
 bool
diff --git a/gcc/c/c-fold.c b/gcc/c/c-fold.c
index 5776f1b..be6a0fc 100644
--- a/gcc/c/c-fold.c
+++ b/gcc/c/c-fold.c
@@ -668,3 +668,13 @@ c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands,
     }
   return ret;
 }
+
+/* Fold X for consideration by one of the warning functions when checking
+   whether an expression has a constant value.  */
+
+tree
+fold_for_warn (tree x)
+{
+  /* The C front-end has already folded X appropriately.  */
+  return x;
+}
diff --git a/gcc/cp/expr.c b/gcc/cp/expr.c
index 7d79215..b1ab453 100644
--- a/gcc/cp/expr.c
+++ b/gcc/cp/expr.c
@@ -315,3 +315,18 @@ mark_exp_read (tree exp)
     }
 }
 
+/* Fold X for consideration by one of the warning functions when checking
+   whether an expression has a constant value.  */
+
+tree
+fold_for_warn (tree x)
+{
+  /* C++ implementation.  */
+
+  /* It's not generally safe to fully fold inside of a template, so
+     call fold_non_dependent_expr instead.  */
+  if (processing_template_decl)
+    return fold_non_dependent_expr (x);
+
+  return c_fully_fold (x, /*for_init*/false, /*maybe_constp*/NULL);
+}
diff --git a/gcc/testsuite/g++.dg/wrappers/pr83814.C b/gcc/testsuite/g++.dg/wrappers/pr83814.C
new file mode 100644
index 0000000..b9f8faa
--- /dev/null
+++ b/gcc/testsuite/g++.dg/wrappers/pr83814.C
@@ -0,0 +1,70 @@
+/* Verify that our memset warnings don't crash when folding
+   arguments within a template (PR c++/83814).  */
+
+// { dg-options "-Wno-int-to-pointer-cast -Wmemset-transposed-args -Wmemset-elt-size" }
+
+template <class>
+void test_1()
+{
+  __builtin_memset (int() - char(), 0, 0);
+}
+
+template <class>
+void test_2()
+{
+  __builtin_memset (0, 0, int() - char());
+}
+
+template <class>
+void test_3 (unsigned a, int c)
+{
+  __builtin_memset((char *)c + a, 0, a);
+}
+
+template <class>
+void test_4 (unsigned a, int c)
+{
+  __builtin_memset(0, 0, (char *)c + a);
+}
+
+/* Verify that we warn for -Wmemset-transposed-args inside
+   a template.  */
+
+char buf[1024];
+
+template <class>
+void test_5 ()
+{
+  __builtin_memset (buf, sizeof buf, 0); // { dg-warning "transposed parameters" }
+}
+
+/* Adapted from c-c++-common/memset-array.c; verify that 
+   -Wmemset-elt-size works within a template.  */
+
+enum a {
+  a_1,
+  a_2,
+  a_n
+};
+int t1[20];
+int t2[a_n];
+
+struct s
+{
+  int t[20];
+};
+
+template<class>
+void foo (struct s *s)
+{
+  __builtin_memset (t1, 0, 20); // { dg-warning "element size" }
+
+  // This case requires reading through an enum value:
+  __builtin_memset (t2, 0, a_n); // { dg-warning "element size" }
+
+  __builtin_memset (s->t, 0, 20); // { dg-warning "element size" }
+
+  // These cases require folding of arg2 within a template:
+  __builtin_memset (t2, 0, a_n + 0); // { dg-warning "element size" }
+  __builtin_memset (t2, 0, a_n * 1); // { dg-warning "element size" }
+}
diff --git a/gcc/testsuite/g++.dg/wrappers/pr83902.C b/gcc/testsuite/g++.dg/wrappers/pr83902.C
new file mode 100644
index 0000000..3d334e7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/wrappers/pr83902.C
@@ -0,0 +1,9 @@
+extern "C" void *memset (void *, int, __SIZE_TYPE__);
+void *p;
+
+template <int T>
+struct B
+{
+  void foo () { memset (p, 0, 4 * T * sizeof(float)); }
+};
+
-- 
1.8.5.3