On Mon, Nov 07, 2016 at 09:29:26PM +0100, Bernd Schmidt wrote:
> On 10/31/2016 08:56 PM, Dominik Vogt wrote:
>
> >combine_simplify_rtx() tries to replace rtx expressions with just two
> >possible values with an experession that uses if_then_else:
> >
> > (if_then_else (condition) (value1) (value2))
> >
> >If the original expression is e.g.
> >
> > (and (reg) (const_int 2))
>
> I'm not convinced that if_then_else_cond is the right place to do
> this. That function is designed to answer the question of whether an
> rtx has exactly one of two values and under which condition; I feel
> it should continue to work this way.
>
> Maybe simplify_ternary_expression needs to be taught to deal with this case?
But simplify_ternary_expression isn't called with the following
test program (only tried it on s390x):
void bar(int, int);
int foo(int a, int *b)
{
if (a)
bar(0, *b & 2);
return *b;
}
combine_simplify_rtx() is called with
(sign_extend:DI (and:SI (reg:SI 61) (const_int 2)))
In the switch it calls simplify_unary_operation(), which return
NULL. The next thing it does is call if_then_else_cond(), and
that calls itself with the sign_extend peeled off:
(and:SI (reg:SI 61) (const_int 2))
takes the "BINARY_P (x)" path and returns false. The problem
exists only if the (and ...) is wrapped in ..._extend, i.e. the
ondition dealing with (and ...) directly can be removed from the
patch.
So, all recursive calls to if_then_els_cond() return false, and
finally the condition in
else if (HWI_COMPUTABLE_MODE_P (mode)
&& pow2p_hwi (nz = nonzero_bits (x, mode))
is true.
Thus, if if_then_else_cond should remain unchanged, the only place
to fix this would be after the call to if_then_else_cond() in
combine_simplify_rtx(). Actually, there already is some special
case handling to override the return code of if_then_else_cond():
cond = if_then_else_cond (x, &true_rtx, &false_rtx);
if (cond != 0
/* If everything is a comparison, what we have is highly unlikely
to be simpler, so don't use it. */
---> && ! (COMPARISON_P (x)
&& (COMPARISON_P (true_rtx) || COMPARISON_P (false_rtx))))
{
rtx cop1 = const0_rtx;
enum rtx_code cond_code = simplify_comparison (NE, &cond, &cop1);
---> if (cond_code == NE && COMPARISON_P (cond))
return x;
...
Should be easy to duplicate the test in the if-body, if that is
what you prefer:
...
if (HWI_COMPUTABLE_MODE_P (GET_MODE (x))
&& pow2p_hwi (nz = nonzero_bits (x, GET_MODE (x)))
&& ! ((code == SIGN_EXTEND || code == ZERO_EXTEND)
&& GET_CODE (XEXP (x, 0)) == AND
&& CONST_INT_P (XEXP (XEXP (x, 0), 0))
&& UINTVAL (XEXP (XEXP (x, 0), 0)) == nz))
return x;
(untested)
Ciao
Dominik ^_^ ^_^
--
Dominik Vogt
IBM Germany
