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[Bug tree-optimization/55559] [4.6/4.7/4.8 Regression] Marshalling double through union with inlines, incorrect behavior with -O2
- From: "rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Mon, 03 Dec 2012 12:30:20 +0000
- Subject: [Bug tree-optimization/55559] [4.6/4.7/4.8 Regression] Marshalling double through union with inlines, incorrect behavior with -O2
- Auto-submitted: auto-generated
- References: <bug-55559-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55559
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords|wrong-code |
Status|ASSIGNED |RESOLVED
Resolution| |INVALID
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> 2012-12-03 12:30:20 UTC ---
We ask fold_unary to fold
fold_unary_ignore_overflow_loc (loc=2147483655, code=FIX_TRUNC_EXPR,
type=0x7ffff6d17690, op0=0x7ffff6e23858)
at /space/rguenther/src/svn/trunk/gcc/fold-const.c:8363
(gdb) call debug_tree (type)
<integer_type 0x7ffff6d17690 unsigned int public unsigned SI
size <integer_cst 0x7ffff6d1a0c0 type <integer_type 0x7ffff6d170a8
bitsizetype> constant 32>
unit size <integer_cst 0x7ffff6d1a0e0 type <integer_type 0x7ffff6d17000
sizetype> constant 4>
align 32 symtab 0 alias set -1 canonical type 0x7ffff6d17690 precision 32
min <integer_cst 0x7ffff6d1a100 0> max <integer_cst 0x7ffff6d1a0a0 4294967295>
pointer_to_this <pointer_type 0x7ffff6d270a8>>
(gdb) call debug_tree (op0)
<real_cst 0x7ffff6e23858
type <real_type 0x7ffff6d17f18 double sizes-gimplified DF
size <integer_cst 0x7ffff6d02d40 constant 64>
unit size <integer_cst 0x7ffff6d02d60 constant 8>
align 64 symtab 0 alias set -1 canonical type 0x7ffff6d17f18 precision
64
pointer_to_this <pointer_type 0x7ffff6d1f150>>
constant -1.0e+0>
which ends up in fold_convert_const_int_from_real which returns
0 with TREE_OVERFLOW set.
Note that you end up converting the double -1.0 to unsigned which according
to C99 6.3.1.4 ends up invoking undefined behavior.
GCC's behavior is not ill-defined, your testcase is. That behavior changed
is fine as it is unsefined.