Re: [PATCH v5] Allocate constant size dynamic stack space in the prologue

[Dominik Vogt <vogt at linux dot vnet dot ibm dot com>]

On Thu, Jul 07, 2016 at 12:57:16PM +0100, Dominik Vogt wrote:
> On Wed, Jul 06, 2016 at 02:01:06PM +0200, Bernd Schmidt wrote:
> > There's one thing I don't quite understand and which seems to have
> > changed since v1:
> > 
> > On 07/04/2016 02:19 PM, Dominik Vogt wrote:
> > >@@ -1099,8 +1101,10 @@ expand_stack_vars (bool (*pred) (size_t), struct stack_vars_data *data)
> > >
> > >       /* If there were any, allocate space.  */
> > >       if (large_size > 0)
> > >-	large_base = allocate_dynamic_stack_space (GEN_INT (large_size), 0,
> > >-						   large_align, true);
> > >+	{
> > >+	  large_allocsize = GEN_INT (large_size);
> > >+	  get_dynamic_stack_size (&large_allocsize, 0, large_align, NULL);
> > >+	}
> > >     }
> > >
> > >   for (si = 0; si < n; ++si)
> > >@@ -1186,6 +1190,19 @@ expand_stack_vars (bool (*pred) (size_t), struct stack_vars_data *data)
> > > 	  /* Large alignment is only processed in the last pass.  */
> > > 	  if (pred)
> > > 	    continue;
> > >+
> > >+	  if (large_allocsize && ! large_allocation_done)
> > >+	    {
> > >+	      /* Allocate space the virtual stack vars area in the
> > >+	         prologue.  */
> > >+	      HOST_WIDE_INT loffset;
> > >+
> > >+	      loffset = alloc_stack_frame_space
> > >+		(INTVAL (large_allocsize),
> > >+		 PREFERRED_STACK_BOUNDARY / BITS_PER_UNIT);
> > >+	      large_base = get_dynamic_stack_base (loffset, large_align);
> > >+	      large_allocation_done = true;
> > >+	    }
> > > 	  gcc_assert (large_base != NULL);
> > >
> > 
> > Why is this code split between the two places here?
> 
> This is a bugfix from v1 to v2.
> I think I had to move this code to the second loop so that the
> space for dynamically aligned variables is allocated at the "end"
> of the space for stack variables.  I cannot remember what the bug
> was, but maybe it was that the variables with fixed and static
> alignment ended up at the same address.
> 
> Anyway, now that the new allocation strategy is used
> unconditionally, it should be possible to move the
> get_dynamic_stack_size call down to the second loop and simplify
> the code somewhat.  I'll look into that.

Version 5 with some code moved from the first loop to the second.

Ciao

Dominik ^_^  ^_^

-- 

Dominik Vogt
IBM Germany