2015-12-04  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/68680

	* calls.c (special_function_p): Return ECF_MAY_BE_ALLOCA for

	BUILT_IN_ALLOCA{,_WITH_ALIGN}.

	* gcc.target/i386/pr68680.c: New test.

--- gcc/calls.c	(revision 231278)

+++ gcc/calls.c	(revision 231279)

@@ -564,6 +564,17 @@ special_function_p (const_tree fndecl, i

 	flags |= ECF_NORETURN;

     }

+  if (DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL)

+    switch (DECL_FUNCTION_CODE (fndecl))

+      {

+      case BUILT_IN_ALLOCA:

+      case BUILT_IN_ALLOCA_WITH_ALIGN:

+	flags |= ECF_MAY_BE_ALLOCA;

+	break;

+      default:

+	break;

+      }

+

   return flags;

 }

--- gcc/testsuite/gcc.target/i386/pr68680.c	(revision 0)

+++ gcc/testsuite/gcc.target/i386/pr68680.c	(revision 231279)

@@ -0,0 +1,15 @@

+/* PR tree-optimization/68680 */

+/* { dg-do compile } */

+/* { dg-options "-O2 -fstack-protector-strong" } */

+

+int foo (char *);

+

+int

+bar (unsigned long x)

+{

+  char a[x];

+  return foo (a);

+}

+

+/* Verify that this function is stack protected.  */

+/* { dg-final { scan-assembler "stack_chk_fail" } } */