Re: patch to fix constant math - first small patch - patch ping for the next stage 1

[Richard Biener <richard dot guenther at gmail dot com>]

On Sun, Mar 31, 2013 at 7:51 PM, Kenneth Zadeck
<zadeck@naturalbridge.com> wrote:
> richard,
>
> I was able to add everything except for the checking asserts.    While I
> think that this is a reasonable idea, it is difficult to add that to a
> function that is defined in hwint.h because of circular includes.   I could
> move this another file (though this appears to be the logical correct place
> for it), or we can do without the asserts.
>
> The context is that [sz]ext_hwi is that are used are over the compiler but
> are generally written out long.   The wide-int class uses them also, but
> wide-int did not see like the right place for them to live and i believe
> that you suggested that i move them.
>
> ok to commit, or do you have a suggested resolution to the assert issue?

Yes, do

#ifdef ENABLE_CHECKING
extern HOST_WIDE_INT sext_hwi (HOST_WIDE_INT, unsigned int);
#else
+/* Sign extend SRC starting from PREC.  */
+
+static inline HOST_WIDE_INT
+sext_hwi (HOST_WIDE_INT src, unsigned int prec)
+{
+  if (prec == HOST_BITS_PER_WIDE_INT)
+    return src;
+  else
+    {
        int shift = HOST_BITS_PER_WIDE_INT - prec;
+      return (src << shift) >> shift;
+    }
+}
#endif

and for ENABLE_CHECKING only provide an out-of-line implementation
in hwint.c.  That's how we did it with abs_hwi (well, we just do not provide
an inline variant there - that's another possibility).

Note that hwint.h is always included after config.h so the ENABLE_CHECKING
definition should be available.

Richard.

>
> kenny
>
>
> On 03/27/2013 10:13 AM, Richard Biener wrote:
>>
>> On Wed, Feb 27, 2013 at 1:22 AM, Kenneth Zadeck
>> <zadeck@naturalbridge.com> wrote:
>>>
>>> Here is the first of my wide int patches with joseph's comments and the
>>> patch rot removed.
>>>
>>> I would like to get these pre approved for the next stage 1.
>>
>> +      int shift = HOST_BITS_PER_WIDE_INT - (prec &
>> (HOST_BITS_PER_WIDE_INT - 1));
>>
>> I think this should gcc_checking_assert that prec is not out of range
>> (any reason why prec is signed int and not unsigned int?) rather than
>> ignore bits in prec.
>>
>> +static inline HOST_WIDE_INT
>> +zext_hwi (HOST_WIDE_INT src, int prec)
>> +{
>> +  if (prec == HOST_BITS_PER_WIDE_INT)
>> +    return src;
>> +  else
>> +    return src & (((HOST_WIDE_INT)1
>> +                  << (prec & (HOST_BITS_PER_WIDE_INT - 1))) - 1);
>> +}
>>
>> likewise.  Also I'm not sure I agree about the signedness of the result /
>> src.
>> zext_hwi (-1, HOST_BITS_PER_WIDE_INT) < 0 is true which is odd.
>>
>> The patch misses context of uses, so I'm not sure what the above functions
>> are intended to do.
>>
>> Richard.
>>
>>> On 10/05/2012 08:14 PM, Joseph S. Myers wrote:
>>>>
>>>> On Fri, 5 Oct 2012, Kenneth Zadeck wrote:
>>>>
>>>>> +# define HOST_HALF_WIDE_INT_PRINT "h"
>>>>
>>>> This may cause problems on hosts not supporting %hd (MinGW?), and
>>>> there's
>>>> no real need for using "h" here given the promotion of short to int; you
>>>> can just use "" (rather than e.g. needing special handling in
>>>> xm-mingw32.h
>>>> like is done for HOST_LONG_LONG_FORMAT).
>>>>
>