[Patch] PR 65315 - Fix alignment of local variables

["Steve Ellcey " <sellcey at imgtec dot com>]

While examining some MIPS code I noticed that GCC did not seem to be 
fully honoring the aligned attribute on some local variables.  I submitted
PR middle-end/65315 to record the bug and I think I now understand it and
have a fix.  The problem was that expand_stack_vars seemed to think that
the first entry in stack_vars_sorted would have the largest alignment but
while all the variables that had alignment greater then
MAX_SUPPORTED_STACK_ALIGNMENT would come before all variables whose
alignment was less than MAX_SUPPORTED_STACK_ALIGNMENT, within the variables
with the alignment greater than MAX_SUPPORTED_STACK_ALIGNMENT, they
were sorted by size, not by alignment.

So my fix was to update large_align in expand_stack_vars if needed.

I have verified the fix on the MIPS test case in PR 65315 and am doing a
regression test now.  OK to checkin if there are no regressions?

I wasn't sure how to create a generic test case, I was checking the 
alignment on MIPS by hand by looking for the shift-right/shift-left
instructions that create an aligned pointer but that obviously doesn't
work on other architectures.

Steve Ellcey
sellcey@imgtec.com


2015-03-04  Steve Ellcey  <sellcey@imgtec.com>

	PR middle-end/65315
	* cfgexpand.c (expand_stack_vars): Update large_align to maximum
	needed alignment.


diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index 7dfe1f6..569cd0d 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -973,6 +973,13 @@ expand_stack_vars (bool (*pred) (size_t), struct stack_vars_data *data)
 	  i = stack_vars_sorted[si];
 	  alignb = stack_vars[i].alignb;
 
+	  /* All "large" alignment decls come before all "small" alignment
+	     decls, but "large" alignment decls are not sorted based on
+	     their alignment.  Increase large_align to track the largest
+	     required alignment.  */
+	  if ((alignb * BITS_PER_UNIT) > large_align)
+	    large_align = alignb * BITS_PER_UNIT;
+
 	  /* Stop when we get to the first decl with "small" alignment.  */
 	  if (alignb * BITS_PER_UNIT <= MAX_SUPPORTED_STACK_ALIGNMENT)
 	    break;