This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
[PATCH] Fix overzealous folding
- From: Eric Botcazou <ebotcazou at adacore dot com>
- To: gcc-patches at gcc dot gnu dot org
- Date: Fri, 16 May 2008 13:39:27 +0200
- Subject: [PATCH] Fix overzealous folding
This is a regression present at -O2 -gnatp on mainline and 4.3 branch,
although the underlying problem appears to have been there for ages.
The problem is that the compiler folds
(boolean) (i & 1)
into
(boolean) i & 1
Later VRP determines that i (an integer) is always greater than 0 and thus
computes that the test is always true.
The problematic code is:
/* Convert (T)(x & c) into (T)x & (T)c, if c is an integer
constants (if x has signed type, the sign bit cannot be set
in c). This folds extension into the BIT_AND_EXPR. */
if (INTEGRAL_TYPE_P (type)
&& TREE_CODE (type) != BOOLEAN_TYPE
&& TREE_CODE (op0) == BIT_AND_EXPR
&& TREE_CODE (TREE_OPERAND (op0, 1)) == INTEGER_CST)
Note that it is properly disabled for BOOLEAN_TYPE; but, in Ada, "boolean"
is an ENUMERAL_TYPE with 2 values and the transformation is thus applied.
Tested on i586-suse-linux, OK for mainline and 4.3 branch?
2008-05-16 Eric Botcazou <ebotcazou@adacore.com>
* fold-const.c (fold_unary) <CASE_CONVERT>: Fold the cast
into a BIT_AND_EXPR only for an INTEGER_TYPE.
2008-05-16 Eric Botcazou <ebotcazou@adacore.com>
* gnat.dg/bit_packed_array3.adb: New test.
--
Eric Botcazou
Index: fold-const.c
===================================================================
--- fold-const.c (revision 135325)
+++ fold-const.c (working copy)
@@ -7864,8 +7864,7 @@ fold_unary (enum tree_code code, tree ty
/* Convert (T)(x & c) into (T)x & (T)c, if c is an integer
constants (if x has signed type, the sign bit cannot be set
in c). This folds extension into the BIT_AND_EXPR. */
- if (INTEGRAL_TYPE_P (type)
- && TREE_CODE (type) != BOOLEAN_TYPE
+ if (TREE_CODE (type) == INTEGER_TYPE
&& TREE_CODE (op0) == BIT_AND_EXPR
&& TREE_CODE (TREE_OPERAND (op0, 1)) == INTEGER_CST)
{
-- { dg-do run }
-- { dg-options "-O2 -gnatp" }
procedure Bit_Packed_Array3 is
type Bitmap_T is array (1 .. 10) of Boolean;
pragma Pack (Bitmap_T);
type Maps_T is record
M1 : Bitmap_T;
end record;
pragma Pack (Maps_T);
for Maps_T'Size use 10;
pragma Suppress_Initialization (Maps_T);
Tmap : constant Bitmap_T := (others => True);
Fmap : constant Bitmap_T := (others => False);
Amap : constant Bitmap_T :=
(1 => False, 2 => True, 3 => False, 4 => True, 5 => False,
6 => True, 7 => False, 8 => True, 9 => False, 10 => True);
function Some_Maps return Maps_T is
Value : Maps_T := (M1 => Amap);
begin
return Value;
end;
pragma Inline (Some_Maps);
Maps : Maps_T;
begin
Maps := Some_Maps;
for I in Maps.M1'Range loop
if (I mod 2 = 0 and then not Maps.M1 (I))
or else (I mod 2 /= 0 and then Maps.M1 (I))
then
raise Program_Error;
end if;
end loop;
end;