patch to fix constant math - 4th patch - the wide-int class - patch ping for the next stage 1

[Kenneth Zadeck]

Richard,

I made major changes to wide-int along the lines you suggested. Each of 
the binary operations is now a template.
There are 5 possible implementations of those operations, one for each 
of HWI, unsigned HWI, wide-int, rtl, and tree.   Note that this is not 
exactly as you suggested, but it is along the same lines.

The HWI template sign extends the value to the precision of the first 
operand, the unsigned HWI is the same except that it is an unsigned 
extension.   The wide-int version is used as before, but is in truth 
rarely used.  The rtl and tree "logically" convert the value to a 
wide-int but in practice do something more efficient than converting to 
the wide-int.   What they do is look inside the rtl or the tree and pass 
a pointer to the data and a length to the binary operation.  This is 
perfectly safe in the position of a second operand to the binary 
operation because the lifetime is guaranteed to be very short.  The 
wide-int implementation was also modified to do the same pointer trick 
allowing all 5 templates to share the same use of the data.

Note that currently the tree code is more crufty than one would like.   
This will clean up nicely when the tree-cst is changed to represent the 
value with an array and a length field.

So now, at least for the second operand of binary operations, the 
storage is never copied.    I do not believe that there is a good 
similar trick for the first operand.  i did not consider something like 
wide_int::add (a, b) to be a viable option; it seems to mis the point of 
using an object oriented language.   So I think that you really have to 
copy the data into an instance of a wide int.

However, while all of this avoids ever having to pass a precision into 
the second operand, this patch does preserve the finite math 
implementation of wide-int.    Finite math is really what people expect 
an optimizer to do, because it seamlessly matches what the machine is 
going to do.

I hope at this point, i can get a comprehensive review on these patches. 
   I believe that I have done what is required.

There are two other patches that will be submitted in the next few 
minutes.   The first one is an updated version of the rtl level patch.   
The only changes from what you have seen before are that the binary 
operations now use the templated binary operations.  The second one is 
the first of the tree level patches.   It converts builtins.c to use 
both use wide-int and it removes all assumptions that tree-csts are 
built with two HWIs.

Once builtins.c is accepted, i will convert the rest of the middle end 
patches.   They will all be converted in a similar way.

Kenny
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2013-04-16  Kenneth Zadeck <zadeck@naturalbridge.com>

	* Makefile.in (wide-int.c, wide-int.h): New files.
	* wide-int.c: New file containing implementation of wide_int class.
	* wide-int.h: New file containing public spec for wide_int class.