Registers above R8 corrupt when called through prim import

[pumpkin]

I write a cmm function:

primbug
{
  foreign "C" printf("%d %d %d %d %d %d %d %d %d\n", R1, R2, R3, R4, R5, R6, R7, R8, R9);
  RET_N(R9);
}

and a binding to it in Haskell:

foreign import prim "primbug" primbug :: Int# -> Int# -> Int# -> Int# 
                                      -> Int# -> Int# -> Int# -> Int#
                                      -> Int#
                                      -> Int#

-- This should resemble id
bug :: Int -> Int
bug (I# i) = I# (primbug 0# 111# 222# 333# 444# 555# 666# 777# i)

main = print (bug 888)

and the program outputs:

0 111 222 333 444 555 666 777 0
0

The contents of R9 have been lost somehow! The result of this corruption isn't always 0, if that helps track it down: in my more complicated use case, I'm getting smallish numbers (two hex digits) instead of a legitimate pointer.

I'm attaching a small cabal package to help reproduce it, because it's a pain to build.

[pumpkin]

This bug is, like #5422, caused by pervasive assumptions in the GHC source that no more than 10 (or even 8 or 6 in some places – it isn't consistent) VanillaRegs? will be used.

[ezyang]

At the very least the compiler should complain about foreign prims that have too many arguments.

I think what we actually want here for the intended application (integer-gmp style bindings) is some sort of facility for inlinable C--. In this case, we can reuse the local registers that already hold all of these values, for only a small code increase.

[igloo]

Let's give a better error in 7.4.

[igloo@…]

commit d535ef006d85dbdb7cda2b09c5bc35cb80108909

Author: Ian Lynagh <igloo@earth.li>
Date:   Sun Nov 6 18:11:56 2011 +0000

    Allow the use of R9 and R10 in primops; fixes trac #5423

 compiler/codeGen/CgUtils.hs          |   12 ++++++++++++
 compiler/codeGen/StgCmmUtils.hs      |    6 ++++++
 compiler/nativeGen/PPC/Regs.hs       |    6 ++++++
 compiler/nativeGen/SPARC/RegPlate.hs |    6 ++++++
 compiler/nativeGen/X86/Regs.hs       |    6 ++++++
 includes/rts/Constants.h             |    2 +-
 includes/stg/MachRegs.h              |    6 +++++-
 includes/stg/Regs.h                  |    6 ++++++
 8 files changed, 48 insertions(+), 2 deletions(-)

[igloo]

10 regs can now be used.