From patchwork Thu Sep 29 15:57:10 2011
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Subject: argument of alloca in terms of units or not
Date: Thu, 29 Sep 2011 05:57:10 -0000
From: Tom de Vries <Tom_deVries@mentor.com>
X-Patchwork-Id: 116979
Message-Id: <4E849556.5010901@mentor.com>
To: Richard Guenther <richard.guenther@gmail.com>
Cc: "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>

Richard,

in gimplify_vla_decl, the alloca argument seems to be the size of the vla in units:
...
  t = build_call_expr (t, 1, DECL_SIZE_UNIT (decl));
...

I wonder why we are going through this 8 vs. BITS_PER_UNIT conversion here:
...
  elem_type = build_nonstandard_integer_type (BITS_PER_UNIT, 1);
  n_elem = size * 8 / BITS_PER_UNIT;
  align = MIN (size * 8, BIGGEST_ALIGNMENT);
...
The element size is BITS_PER_UNIT, so 1 unit, and size is in units.

Shouldn't this be:
...
...

Thanks,
- Tom


Index: tree-ssa-ccp.c
===================================================================
--- tree-ssa-ccp.c (revision 179210)
+++ tree-ssa-ccp.c (working copy)
@@ -1722,8 +1722,8 @@ fold_builtin_alloca_for_var (gimple stmt

   /* Declare array.  */
   elem_type = build_nonstandard_integer_type (BITS_PER_UNIT, 1);
-  n_elem = size * 8 / BITS_PER_UNIT;
-  align = MIN (size * 8, BIGGEST_ALIGNMENT);
+  n_elem = size;
+  align = MIN (size * BITS_PER_UNIT, BIGGEST_ALIGNMENT);
   if (align < BITS_PER_UNIT)
     align = BITS_PER_UNIT;
   array_type = build_array_type_nelts (elem_type, n_elem);