[Bug middle-end/47581] [4.6 regression] Unnecessary adjustments to stack pointer

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47581

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-02-02 11:23:18 UTC ---
Before Richard's commit apparently expand_one_var wasn't updating
stack_alignment_needed, just stack_alignment_estimated, now it updates both.
As PREFERRED_STACK_BOUNDARY is 128 (the default), ix86_minimum_alignment:
  if (TARGET_64BIT || align != 64 || ix86_preferred_stack_boundary >= 64)
    return align;
returns 64 instead of 32.

So, to fix this, either the stack_alignment_needed updating in expand_one_var
isn't strictly necessary and we could undo that part of the changes.

Or return 32 as MINIMUM_ALIGNMENT for DImode long long even for
ix86_preferred_stack_boundary >= 64.

Or we could perhaps the
  /* Align start of frame for local function.  */
  offset = (offset + stack_alignment_needed - 1) & -stack_alignment_needed;
in ix86_compute_frame_layout perform only if
  if (offset != frame->sse_reg_save_offset
      || size != 0
      || !current_function_is_leaf
      || cfun->calls_alloca
      || ix86_current_function_calls_tls_descriptor)
(i.e. if frame size is 0 and no outgoing calls, it doesn't make sense to
align).