Re: [Valgrind-users] valgrind breaks any long double operation on x86-64

[Julian S. <js...@ac...>]

>>> But of course, we all agree it would be nice to have 80 bits floats
>>> properly supported by Valgrind.

To support this for 64-bit processes would require, roughly:

* add an F80 (80-bit floating point) type to IR
* add relevant 80-bit equivalents of the relevant IROps
  (AddF80, SubF80, SinF80, etc)
* change the front end (guest_amd64_toIR.c) to generate
  IR that uses those new IROps
* change the back end (host_amd64_isel.c) to generate 80
  bit FP instructions from that IR.

Much of the back end stuff could be imported from the x86 (32-bit)
compilation pipeline.  That already has machinery to generate
x87 code and in particular to deal with the x87 register-stack
wierdness.

That would get a baseline simulator (--tool=none) that works OK,
Getting Memcheck to work requires extra steps:

* add an I80 (80-bit integer) type to IR
* add 80 bit versions of the few IROps that Memcheck requires
  (CmpwNEZ80, CmpNEZ80, Left80)
* add instruction selection to deal with those.  The tricky bit
  is that these will have to be generated into register-pairs,
  in the style of the existing iselInt128Expr, except that only
  the lowest 16 bits of the high-part register is used.

And comprehensive test cases, of course.  These are the most
important single piece, since they can be used to drive the rest
of the development.

J