avoid alignment of static variables affecting stack's

Function (or more narrow) scope static variables (as well as others not
placed on the stack) should also not have any effect on the stack
alignment. I noticed the issue first with Linux'es dynamic_pr_debug()
construct using an 8-byte aligned sub-file-scope local variable.

According to my checking bad behavior started with 4.6.x (4.5.3 was
still okay), but generated code got quite a bit worse as of 4.9.0.

gcc/
2015-12-11  Jan Beulich  <jbeulich@suse.com>

	* cfgexpand.c (expand_one_var): Exit early for static and
	external variables when adjusting stack alignment related.

gcc/testsuite/
2015-12-11  Jan Beulich  <jbeulich@suse.com>

	* gcc.c-torture/execute/stkalign.c: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@231569 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index cb9b10ceb418f876f679a92bb80750ba49ff6e23..b52b9aae8d1f18d4bdc1435e9e9f1695b1d603da 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2015-12-11  Jan Beulich  <jbeulich@suse.com>
+
+       * cfgexpand.c (expand_one_var): Exit early for static and
+       external variables when adjusting stack alignment related.
+
 2015-12-11  Dominik Vogt  <vogt@linux.vnet.ibm.com>
 
        * config/s390/s390.c (s390_rtx_costs)

diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index 7fe02a900bc987fb8525febe4fb04aba3c58b830..7f4eba2c226ea909d503908c34c5c6800de10abb 100644 (file)
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -1550,6 +1550,9 @@ expand_one_var (tree var, bool toplevel, bool really_expand)
 
   if (TREE_TYPE (var) != error_mark_node && TREE_CODE (var) == VAR_DECL)
     {
+      if (is_global_var (var))
+       return 0;
+
       /* Because we don't know if VAR will be in register or on stack,
         we conservatively assume it will be on stack even if VAR is
         eventually put into register after RA pass.  For non-automatic

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 541228af5a179a173fba27d675c6eab42439af1a..1372d841305427da3db5b1ca8a1ec8758cd078be 100644 (file)
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2015-12-11  Jan Beulich  <jbeulich@suse.com>
+
+       * gcc.c-torture/execute/stkalign.c: New.
+
 2015-12-11  Tsvetkova Alexandra  <aleksandra.tsvetkova@intel.com>
 
        * gcc.target/i386/mpx/memmove-1.c: New test.

diff --git a/gcc/testsuite/gcc.c-torture/execute/stkalign.c b/gcc/testsuite/gcc.c-torture/execute/stkalign.c
new file mode 100644 (file)
index 0000000..e8761b9
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/execute/stkalign.c
@@ -0,0 +1,26 @@
+/* { dg-options "-fno-inline" } */
+
+#include <assert.h>
+
+#define ALIGNMENT 64
+
+unsigned test(unsigned n, unsigned p)
+{
+  static struct { char __attribute__((__aligned__(ALIGNMENT))) c; } s;
+  unsigned x;
+
+  assert(__alignof__(s) == ALIGNMENT);
+  asm ("" : "=g" (x), "+m" (s) : "0" (&x));
+
+  return n ? test(n - 1, x) : (x ^ p);
+}
+
+int main (int argc, char *argv[] __attribute__((unused)))
+{
+  unsigned int x = test(argc, 0);
+
+  x |= test(argc + 1, 0);
+  x |= test(argc + 2, 0);
+
+  return !(x & (ALIGNMENT - 1));
+}