Thanks foe the review and suggestions.
On 10/07/14 22:15, Richard Biener wrote:
> On Mon, Jul 7, 2014 at 8:55 AM, Kugan <kugan.vivekanandara...@linaro.org>
> wrote:
[...]
>>
>> For -fwrapv, it is due to how PROMOTE_MODE is defined in arm back-end.
>> In the test-case, a function (which has signed char return type) returns
>> -1 in one of the paths. ARM PROMOTE_MODE changes that to 255 and relies
>> on zero/sign extension generated by RTL again for the correct value. I
>> saw some other targets also defining similar think. I am therefore
>> skipping removing zero/sign extension if the ssa variable can be set to
>> negative integer constants.
>
> Hm? I think you should rather check that you are removing a
> sign-/zero-extension - PROMOTE_MODE tells you if it will sign- or
> zero-extend. Definitely
>
> + /* In some architectures, negative integer constants are truncated and
> + sign changed with target defined PROMOTE_MODE macro. This will impact
> + the value range seen here and produce wrong code if zero/sign extensions
> + are eliminated. Therefore, return false if this SSA can have negative
> + integers. */
> + if (is_gimple_assign (stmt)
> + && (TREE_CODE_CLASS (gimple_assign_rhs_code (stmt)) == tcc_unary))
> + {
> + tree rhs1 = gimple_assign_rhs1 (stmt);
> + if (TREE_CODE (rhs1) == INTEGER_CST
> + && !TYPE_UNSIGNED (TREE_TYPE (ssa))
> + && tree_int_cst_compare (rhs1, integer_zero_node) == -1)
> + return false;
>
> looks completely bogus ... (an unary op with a constant operand?)
> instead you want to do sth like
I see that unary op with a constant operand is not possible in gimple.
What I wanted to check here is any sort of constant loads; but seems
that will not happen in gimple. Is PHI statements the only possible
statements where we will end up with such constants.
> mode = TYPE_MODE (TREE_TYPE (ssa));
> rhs_uns = TYPE_UNSIGNED (TREE_TYPE (ssa));
> PROMOTE_MODE (mode, rhs_uns, TREE_TYPE (ssa));
>
> instead of initializing rhs_uns from ssas type. That is, if
> PROMOTE_MODE tells you to promote _not_ according to ssas sign then
> honor that.
This is triggered in pr43017.c in function foo for arm-none-linux-gnueabi.
where, the gimple statement that cause this looks like:
.....
# _3 = PHI <_17(7), -1(2)>
bb43:
return _3;
ARM PROMOTE_MODE changes the sign for integer constants only and hence
looking at the variable with PROMOTE_MODE is not changing the sign in
this case.
#define PROMOTE_MODE(MODE, UNSIGNEDP, TYPE) \
if (GET_MODE_CLASS (MODE) == MODE_INT \
&& GET_MODE_SIZE (MODE) < 4) \
{ \
if (MODE == QImode) \
UNSIGNEDP = 1; \
else if (MODE == HImode) \
UNSIGNEDP = 1; \
(MODE) = SImode; \
}
>> As for the -fno-strict-overflow case, if the variables overflows, in VRP
>> dumps, I see +INF(OVF), but the value range stored in ssa has TYPE_MAX.
>> We therefore should limit the comparison to (TYPE_MIN < VR_MIN && VR_MAX
>> < TYPE_MAX) instead of (TYPE_MIN <= VR_MIN && VR_MAX <= TYPE_MAX) when
>> checking to be sure that this is not the overflowing case. Attached
>> patch changes this.
>
> I don't think that's necessary - the overflow cases happen only when
> that overflow has undefined behavior, thus any valid program will have
> values <= MAX.
I see that you have now removed +INF(OVF). I will change it this way.
Thanks again,
Kugan
