Re: CmmLint error when doing safe ccall from cmm

[Simon Marlow]

On 20/06/2014 22:23, Yuras Shumovich wrote:
Simon,
Sorry if I'm too stupid, but
do you mean we only support 64-bit results from "prim" call? But I'm
using TO_W_ macro to convert the result to 64-bit value before returning
from cmm function.

The result of your foreign call is a CInt, which is an I32.  If you make 
it an I64 and then convert it to an I32, that should work.

Cheers,
Simon

Or you mean result from "ccall" call?
nativeGen/X86/CodeGen.hs:genCCall64 definitely supports that. And it
works for unsafe "ccall".
Looks like the issue is somewhere in translation from high level cmm to
low level cmm.

Thanks,
Yuras

On Fri, 2014-06-20 at 21:24 +0100, Simon Marlow wrote:
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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