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[wide-int] Do not treat rtxes as sign-extended

Message ID 87siv9jicz.fsf@talisman.default
State New
Headers show

Commit Message

Richard Sandiford Nov. 6, 2013, 10:06 p.m. UTC 
Richard Biener <richard.guenther@gmail.com> writes:
> On Sat, Nov 2, 2013 at 3:25 PM, Richard Sandiford
> <rdsandiford@googlemail.com> wrote:
>> Kenneth Zadeck <zadeck@naturalbridge.com> writes:
>>> On 11/02/2013 06:30 AM, Richard Sandiford wrote:
>>>> Bah.  After all that effort, it turns out that -- by design --
>>>> there is one special case where CONST_INTs are not sign-extended.
>>>> Nonzero/true BImode integers are stored as STORE_FLAG_VALUE,
>>>> which can be 1 rather than -1.  So (const_int 1) can be a valid
>>>> BImode integer -- and consequently (const_int -1) can be wrong --
>>>> even though BImode only has 1 bit.
>>>>
>>>> It might be nice to change that, but for wide-int I think we should
>>>> just treat rtxes like trees for now.
>>>>
>>>> Tested on powerpc64-linux-gnu and x86_64-linux-gnu.  It fixes some ICEs
>>>> seen on bfin-elf.  OK to install?
>>> do we have to throw away the baby with the bath water here?  I guess
>>> what you are saying is that it is worse to have is_sign_extended be a
>>> variable that is almost always true than to be a hard false.
>>
>> Right.  is_sign_extended is only useful if it's a compile-time value.
>> Making it a run-time value would negate the benefit.
>>
>> I think in practice STORE_FLAG_VALUE is a compile-time constant too,
>> so we could set is_sign_extended to STORE_FLAG_VALUE == -1.  But AFAICT
>> that would only help SPU and m68k.
>>
>>> also we could preserve the test and make it not apply to bimode.
>>
>> You mean the one in the assert?  Yeah, OK.  How about this version?
>>
>> Richard
>>
>>
>> Index: gcc/rtl.h
>> ===================================================================
>> --- gcc/rtl.h   2013-11-02 11:06:12.738517644 +0000
>> +++ gcc/rtl.h   2013-11-02 14:22:05.636007860 +0000
>> @@ -1408,7 +1408,9 @@ typedef std::pair <rtx, enum machine_mod
>>    {
>>      static const enum precision_type precision_type = VAR_PRECISION;
>>      static const bool host_dependent_precision = false;
>> -    static const bool is_sign_extended = true;
>> +    /* This ought to be true, except for the special case that BImode
>> +       is canonicalized to STORE_FLAG_VALUE, which might be 1.  */
>> +    static const bool is_sign_extended = false;
>>      static unsigned int get_precision (const rtx_mode_t &);
>>      static wi::storage_ref decompose (HOST_WIDE_INT *, unsigned int,
>>                                       const rtx_mode_t &);
>> @@ -1432,7 +1434,8 @@ wi::int_traits <rtx_mode_t>::decompose (
>>      case CONST_INT:
>>        if (precision < HOST_BITS_PER_WIDE_INT)
>>         gcc_checking_assert (INTVAL (x.first)
>> -                            == sext_hwi (INTVAL (x.first), precision));
>> +                            == sext_hwi (INTVAL (x.first), precision)
>> +                            || (precision == 1 && INTVAL (x.first) == 1));
>
> please add a comment here (and a check for BImode?).

OK, done as follows.

Thanks,
Richard
diff mbox

Patch

Index: gcc/rtl.h
===================================================================
--- gcc/rtl.h	2013-11-06 21:53:29.013756409 +0000
+++ gcc/rtl.h	2013-11-06 22:02:08.199889647 +0000
@@ -1433,9 +1433,11 @@  wi::int_traits <rtx_mode_t>::decompose (
     {
     case CONST_INT:
       if (precision < HOST_BITS_PER_WIDE_INT)
+	/* Nonzero BImodes are stored as STORE_FLAG_VALUE, which on many
+	   targets is 1 rather than -1.  */
 	gcc_checking_assert (INTVAL (x.first)
 			     == sext_hwi (INTVAL (x.first), precision)
-			     || (precision == 1 && INTVAL (x.first) == 1));
+			     || (x.second == BImode && INTVAL (x.first) == 1));
 
       return wi::storage_ref (&INTVAL (x.first), 1, precision);