On 05/01/2014 11:46, Herbert Valerio Riedel wrote:
On 2014-01-05 at 01:15:53 +0100, Carter Schonwald wrote:
hey Herbert,
I generally start with looking at the primops.cmm file for examples
https://github.com/ghc/ghc/blob/master/rts/PrimOps.cmm#L572-L588
stg_decodeFloatzuIntzh ( F_ arg )
{
W_ p, mp_tmp1, W_ mp_tmp_w;
STK_CHK_GEN_N (WDS(2));
mp_tmp1 = Sp - WDS(1);
mp_tmp_w = Sp - WDS(2);
ccall __decodeFloat_Int(mp_tmp1 "ptr", mp_tmp_w "ptr", arg);
return (W_[mp_tmp1], W_[mp_tmp_w]);
}
that function in particular is compiled to
[stg_decodeFloatzuIntzh() // [F1]
{ info_tbl: []
stack_info: arg_space: 8 updfr_space: Just 8
}
{offset
cc: _c0::F32 = F1;
goto c4;
c4: if ((old + 0) - 2 * 8 < SpLim) goto c6; else goto c7;
c6: I64[(young<c5> + 8)] = c5;
call stg_gc_noregs() returns to c5, args: 8, res: 8, upd: 8;
c5: goto c4;
c7: _c2::I64 = Sp - 1 * 8;
_c3::I64 = Sp - 2 * 8;
_c8::I64 = __decodeFloat_Int;
_c9::I64 = _c2::I64;
_ca::I64 = _c3::I64;
_cb::F32 = _c0::F32;
call "ccall" arg hints: [PtrHint, PtrHint,] result hints: []
(_c8::I64)(_c9::I64, _ca::I64, _cb::F32);
R2 = I64[_c3::I64];
R1 = I64[_c2::I64];
call (P64[(old + 8)])(R2, R1) args: 8, res: 0, upd: 8;
}
}]
But I see no effort to adjust Sp (i.e. `Sp = Sp - 16`) right before the
call to __decodeFloat_Int; how is it ensured that __decodeFloat_Int
doesn't use the locations Sp-8 and Sp-16 for as its local stack?
__decodeFloat_Int is a C function, so it will not touch the Haskell stack.
Cheers,
Simon
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