UNREG: fix CmmRegOff large offset handling on W64 platforms

Gabor noticed C warning when building unregisterised
64-bit compiler on GHC.Integer.Types (from integer-simple).

Minimised example with a warning:

```haskell
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# OPTIONS_GHC -Wall #-}

module M (bug) where

import GHC.Prim (Word#, minusWord#, ltWord#)
import GHC.Types (isTrue#)

-- assume Word = Word64
bug :: Word# -> Word#
bug x = if isTrue# (x `ltWord#` 0x8000000000000000##) then 0##
        else x `minusWord#` 0x8000000000000000##
```

```
$ LANG=C x86_64-UNREG-linux-gnu-ghc -O1 -c M.hs -fforce-recomp
/tmp/ghc30219_0/ghc_1.hc: In function 'M_bug_entry':

/tmp/ghc30219_0/ghc_1.hc:20:14: error:
     warning: integer constant is so large that it is unsigned
```

It's caused by limited handling of integer literals in CmmRegOff.
This change switches to use standard integer literal pretty-printer.

C code before the change:

```c
FN_(M_bug_entry) {
W_ _sAg;
_cAr:
_sAg = *Sp;
switch ((W_)(_sAg < 0x8000000000000000UL)) {
case 0x1UL: goto _cAq;
default: goto _cAp;
}
_cAp:
R1.w = _sAg+-9223372036854775808;
// ...
```

C code after the change:

```c
FN_(M_bug_entry) {
W_ _sAg;
_cAr:
_sAg = *Sp;
switch ((W_)(_sAg < 0x8000000000000000UL)) {
case 0x1UL: goto _cAq;
default: goto _cAp;
}
_cAp:
R1.w = _sAg+(-0x8000000000000000UL);
```

URL: https://mail.haskell.org/pipermail/ghc-devs/2018-June/015875.html
Reported-by: Gabor Greif
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

Test Plan: test generated code on unregisterised mips64 and amd64

Reviewers: simonmar, ggreif, bgamari

Reviewed By: ggreif, bgamari

Subscribers: rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4856

0 files changed, 0 insertions, 0 deletions