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.

From-SVN: r231569

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index cb9b10c..b52b9aa 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 7fe02a9..7f4eba2 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 541228a..1372d84 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));
+}