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?
otoh, the comments in cmmparse.y indicate that's not quite "kosher"? or maybe the comments are a lie? https://github.com/ghc/ghc/blob/master/compiler/cmm/CmmParse.y#L24-L28