Re: C PATCH for c/70093 (ICE with nested-function returning VM type)

[Marek Polacek <polacek at redhat dot com>]

On Wed, Mar 09, 2016 at 12:24:42PM +0100, Jakub Jelinek wrote:
> On Wed, Mar 09, 2016 at 12:05:51PM +0100, Marek Polacek wrote:
> > This PR points out that nested functions returning VM types don't work as
> > expected (yeah, go figure).  We got an ICE on the testcase because we were
> > trying to allocate variable-sized temporary instead of using __builtin_alloca
> > or its kin.  Jakub suggested to follow what the C++ front end does here.  It
> > seems to be the case that it creates a TARGET_EXPR if the call doesn't have
> > a LHS.  That seems to work out well.  The run-time testcase sanity-checks that
> > we do something reasonable.
> > 
> > Not a regression, but on the other hand the patch doesn't change anything for
> > 99.9% programs out there.
> 
> Wonder if you still can get an ICE if you add __attribute__((noreturn)) to
> such nested function.  Quick grep shows that there are some suspicious spots
> and others are fine:
[...]

Wow, indeed it ICEs with __attribute__((noreturn)).  Technically, only the
gimplify.c part is needed to fix the new ICE, but I've also fixed the
cgraphunit.c spot for good measure.  New compile test added.

Bootstrapped/regtested on x86_64-linux, ok for trunk or gcc-7?

2016-03-09  Marek Polacek  <polacek@redhat.com>

	PR c/70093
	* c-typeck.c (build_function_call_vec): Create a TARGET_EXPR for
	nested functions returning VM types.

	* cgraphunit.c (cgraph_node::expand_thunk): Also build call to the
	function being thunked if the result type doesn't have fixed size.
	* gimplify.c (gimplify_modify_expr): Also set LHS if the result type
	doesn't have fixed size.

	* gcc.dg/nested-func-10.c: New test.
	* gcc.dg/nested-func-9.c: New test.

diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
index 6aa0f03..de9d465 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -3068,6 +3068,16 @@ build_function_call_vec (location_t loc, vec<location_t> arg_loc,
     result = build_call_array_loc (loc, TREE_TYPE (fntype),
 				   function, nargs, argarray);
 
+  /* In this improbable scenario, a nested function returns a VM type.
+     Create a TARGET_EXPR so that the call always has a LHS, much as
+     what the C++ FE does for functions returning non-PODs.  */
+  if (variably_modified_type_p (TREE_TYPE (fntype), NULL_TREE))
+    {
+      tree tmp = create_tmp_var_raw (TREE_TYPE (fntype));
+      result = build4 (TARGET_EXPR, TREE_TYPE (fntype), tmp, result,
+		       NULL_TREE, NULL_TREE);
+    }
+
   if (VOID_TYPE_P (TREE_TYPE (result)))
     {
       if (TYPE_QUALS (TREE_TYPE (result)) != TYPE_UNQUALIFIED)
diff --git gcc/cgraphunit.c gcc/cgraphunit.c
index 8b3fddc..4351ae4 100644
--- gcc/cgraphunit.c
+++ gcc/cgraphunit.c
@@ -1708,7 +1708,9 @@ cgraph_node::expand_thunk (bool output_asm_thunks, bool force_gimple_thunk)
 
       /* Build call to the function being thunked.  */
       if (!VOID_TYPE_P (restype)
-	  && (!alias_is_noreturn || TREE_ADDRESSABLE (restype)))
+	  && (!alias_is_noreturn
+	      || TREE_ADDRESSABLE (restype)
+	      || TREE_CODE (TYPE_SIZE_UNIT (restype)) != INTEGER_CST))
 	{
 	  if (DECL_BY_REFERENCE (resdecl))
 	    {
diff --git gcc/gimplify.c gcc/gimplify.c
index b331e41..692d168 100644
--- gcc/gimplify.c
+++ gcc/gimplify.c
@@ -4838,7 +4838,8 @@ gimplify_modify_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p,
 	}
       notice_special_calls (call_stmt);
       if (!gimple_call_noreturn_p (call_stmt)
-	  || TREE_ADDRESSABLE (TREE_TYPE (*to_p)))
+	  || TREE_ADDRESSABLE (TREE_TYPE (*to_p))
+	  || TREE_CODE (TYPE_SIZE_UNIT (TREE_TYPE (*to_p))) != INTEGER_CST)
 	gimple_call_set_lhs (call_stmt, *to_p);
       assign = call_stmt;
     }
diff --git gcc/testsuite/gcc.dg/nested-func-10.c gcc/testsuite/gcc.dg/nested-func-10.c
index e69de29..1b869ac 100644
--- gcc/testsuite/gcc.dg/nested-func-10.c
+++ gcc/testsuite/gcc.dg/nested-func-10.c
@@ -0,0 +1,45 @@
+/* PR c/70093 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+void
+foo (int n)
+{
+  struct S { int a[n]; };
+
+  struct S __attribute__((noreturn))
+  fn (void)
+  {
+    struct S s;
+    s.a[0] = 42;
+    return s; /* { dg-warning "function declared .noreturn.|.noreturn. function does return" } */
+  }
+
+  auto struct S __attribute__((noreturn))
+  fn2 (void)
+  {
+    return fn (); /* { dg-warning "function declared .noreturn." } */
+  }
+
+  struct S x;
+  x = fn ();
+
+  if (x.a[0] != 42)
+    __builtin_abort ();
+
+  if (fn ().a[0] != 42)
+    __builtin_abort ();
+
+  __typeof__ (fn ()) *p = &x;
+  if (p->a[0] != 42)
+    __builtin_abort ();
+
+  if (fn2 ().a[0] != 42)
+    __builtin_abort ();
+}
+
+int
+main (void)
+{
+  foo (1);
+}
diff --git gcc/testsuite/gcc.dg/nested-func-9.c gcc/testsuite/gcc.dg/nested-func-9.c
index e69de29..b703f3a 100644
--- gcc/testsuite/gcc.dg/nested-func-9.c
+++ gcc/testsuite/gcc.dg/nested-func-9.c
@@ -0,0 +1,45 @@
+/* PR c/70093 */
+/* { dg-do run } */
+/* { dg-options "" } */
+
+void
+foo (int n)
+{
+  struct S { int a[n]; };
+
+  struct S
+  fn (void)
+  {
+    struct S s;
+    s.a[0] = 42;
+    return s;
+  }
+
+  auto struct S
+  fn2 (void)
+  {
+    return fn ();
+  }
+
+  struct S x;
+  x = fn ();
+
+  if (x.a[0] != 42)
+    __builtin_abort ();
+
+  if (fn ().a[0] != 42)
+    __builtin_abort ();
+
+  __typeof__ (fn ()) *p = &x;
+  if (p->a[0] != 42)
+    __builtin_abort ();
+
+  if (fn2 ().a[0] != 42)
+    __builtin_abort ();
+}
+
+int
+main (void)
+{
+  foo (1);
+}

	Marek