CmmLint error when doing safe ccall from cmm

[Simon Marlow]

On 20/06/14 15:03, Yuras Shumovich wrote:
> Hello,
>
> I'm trying to do safe ccall from cmm (see below for the code). It seems
> to work, but -dcmm-lint is not satisfied:
>
> /opt/ghc-7.8.2/bin/ghc --make -o test hs.hs cmm.cmm c.c -dcmm-lint -fforce-recomp
> Cmm lint error:
>    in basic block c4
>      in assignment:
>        _c1::I32 = R1;
>        Reg ty: I32
>        Rhs ty: I64
> Program was:
>    {offset
>      c5: _c0::I64 = R1;
>          _c2::I64 = c_test;
>          _c3::I32 = %MO_UU_Conv_W64_W32(_c0::I64);
>          I64[(young<c4> + 8)] = c4;
>          foreign call "ccall" arg hints:  []  result hints:  [] (_c2::I64)(...) returns to c4 args: ([_c3::I32]) ress: ([_c1::I32])ret_args: 8ret_off: 8;
>      c4: _c1::I32 = R1;
>          R1 = %MO_SS_Conv_W32_W64(_c1::I32);
>          call (P64[(old + 8)])(R1) args: 8, res: 0, upd: 8;
>    }
>
> <no location info>:
> Compilation had errors

I believe we only support 64-bit results on a 64-bit platform, but we 
you can always narrow to 32 bits with an MO_Conv afterwards if you want. 
  This is essentially what happens when you call a function that returns 
CInt using the FFI - you can always try that and see what Cmm you get.

Also, I'll be mildly surprised if using safe foreign calls from 
hand-written Cmm works, since I don't believe we use them anywhere so it 
isn't likely to be well tested :-)

Cheers,
Simon


> The same code without "safe" annotation passes cmm lint. Is it my error
> or ghc bug? How can I do safe ccall in cmm correctly?
>
> Here is the code:
>
> == c.c ==
> #include <assert.h>
>
> int c_test(int i)
> {
>    assert(i == 1);
>    return 2;
> }
>
> == cmm.cmm
> #include "Cmm.h"
>
> cmm_test(W_ i)
> {
>    CInt i1;
>    (i1) = ccall c_test(W_TO_INT(i)) "safe";
>    return (TO_W_(i1));
> }
>
> == hs.hs ==
> {-# LANGUAGE GHCForeignImportPrim #-}
> {-# LANGUAGE ForeignFunctionInterface #-}
> {-# LANGUAGE MagicHash #-}
> {-# LANGUAGE UnboxedTuples #-}
> {-# LANGUAGE UnliftedFFITypes #-}
>
> import GHC.Prim
> import GHC.Types
> import Control.Exception
>
> foreign import prim "cmm_test" test :: Int# -> Int#
>
> main :: IO ()
> main = do
>    let i1 = test 1#
>    assert (I# i1 == 2) (return ())
>
>
> Thanks,
> Yuras
>
>
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