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Re: [PATCH 2/2] Enable elimination of zext/sext


On 14 July 2014 04:58:17 Kugan <kugan.vivekanandarajah@linaro.org> wrote:

On 11/07/14 22:47, Richard Biener wrote:
> On Fri, Jul 11, 2014 at 1:52 PM, Kugan
> <kugan.vivekanandarajah@linaro.org> wrote:
>> 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.vivekanandarajah@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.
>
> No, in theory you can have
>
>   ssa_1 = -1;
>
> but that's not unary but a GIMPLE_SINGLE_RHS and thus
> gimple_assign_rhs_code (stmt) == INTEGER_CST.
>
>>>   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;                          \
>>     }
>
> Where does it only apply for "constants"?  It applies to all QImode and
> HImode entities.

oops, sorry. I donât know what I was thinking or looking at when I wrote
that :( It indeed fixes my problems. Thanks for that.

Here is the modified patch. Bootstrapped and regression tested for
86_64-unknown-linux-gnu and arm-none-linux-gnueabi with no new regressions.


Is this OK?

Thanks,
Kugan


gcc/

2014-07-14  Kugan Vivekanandarajah  <kuganv@linaro.org>

	* calls.c (precompute_arguments): Check is_promoted_for_type
	and set the promoted mode.
	(is_promoted_for_type): New function.

Don't we name predicates more like promoted_for_type_p?

Thanks,
	(expand_expr_real_1): Check is_promoted_for_type
	and set the promoted mode.
	* expr.h (is_promoted_for_type): New function definition.
	* cfgexpand.c (expand_gimple_stmt_1): Call emit_move_insn if
	SUBREG is promoted with SRP_SIGNED_AND_UNSIGNED.


gcc/testsuite
2014-07-14  Kugan Vivekanandarajah  <kuganv@linaro.org>

	* gcc.dg/zero_sign_ext_test.c: New test.



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