On Tue, Oct 18, 2016 at 8:35 AM, Eric Botcazou <ebotcazou@adacore.com> wrote:
Hi,
this is a regression present on the mainline and 6 branch: the compiler now
generates wrong code for the attached testcase at -O because of an internal
conflict about boolean types. The sequence is as follows. In .mergephi3:
boolean _22;
p__enum res;
<bb 9>:
if (_22 != 0)
goto <bb 10>;
else
goto <bb 11>;
<bb 10>:
<bb 11>:
# res_17 = PHI <2(8), 0(9), 1(10)>
is turned into:
COND_EXPR in block 9 and PHI in block 11 converted to straightline code.
PHI res_17 changed to factor conversion out from COND_EXPR.
New stmt with CAST that defines res_17.
boolean _33;
<bb 10>:
# _33 = PHI <2(8), _22(9)>
res_17 = (p__enum) _33;
[...]
<bb 12>:
if (res_17 != 0)
goto <bb 13>;
else
goto <bb 14>;
<bb 13>:
_12 = res_17 == 2;
_13 = (integer) _12
in .phiopt1. So boolean _33 can have value 2. Later forwprop3 propagates _33
into the uses of res_17:
<bb 12>:
if (_33 != 0)
goto <bb 13>;
else
goto <bb 14>;
<bb 13>:
_12 = _33 == 2;
_13 = (integer) _12;
and DOM3 deduces:
<bb 13>:
_12 = 0;
_13 = 0;
because it computes that _33 has value 1 in BB 13 since it's a boolean.
The problem was introduced by the new factor_out_conditional_conversion:
/* If arg1 is an INTEGER_CST, fold it to new type. */
if (INTEGRAL_TYPE_P (TREE_TYPE (new_arg0))
&& int_fits_type_p (arg1, TREE_TYPE (new_arg0)))
{
if (gimple_assign_cast_p (arg0_def_stmt))
new_arg1 = fold_convert (TREE_TYPE (new_arg0), arg1);
else
return NULL;
}
else
return NULL
int_fits_type_p is documented as taking only INTEGER_TYPE, but is invoked
on constant 2 and a BOOLEAN_TYPE and returns true.
BOOLEAN_TYPE is special in Ada: it has precision 8 and range [0;255] so the
outcome of int_fits_type_p is not unreasonable. But this goes against the
various transformations applied to boolean types in the compiler, which all
assume that they can only take values 0 or 1.
Hence the attached fix (which should be a no-op except for Ada), tested on
x86_64-suse-linux, OK for mainline and 6 branch?
Hmm, I wonder if the patch is a good approach as you are likely only papering
over a single of possibly very many affected places (wi::fits_to_tree_p comes
immediately to my mind). I suppose a better way would be for Ada to not
lie about those types and not use BOOLEAN_TYPE but INTEGER_TYPE.
Because BOOLEAN_TYPE types only have two values as documented in
tree.def:
/* Boolean type (true or false are the only values). Looks like an
INTEGRAL_TYPE. */
DEFTREECODE (BOOLEAN_TYPE, "boolean_type", tcc_type, 0)
There are not many references to BOOLEAN_TYPE in ada/gcc-interface
thus it shouldn't be hard to change ... (looks like Ada might even prefer
ENUMERAL_TYPE here).
Thanks,
Richard.
2016-10-18 Eric Botcazou <ebotcazou@adacore.com>
* tree.c (int_fits_type_p): Accept only 0 and 1 for boolean types.