I think the bug might be here:
inlineStmt u a (CmmCall target regs es srt ret)
= CmmCall (infn target) regs es' srt ret
where infn (CmmCallee fn cconv) = CmmCallee fn cconv
infn (CmmPrim p) = CmmPrim p
es' = [ (CmmHinted (inlineExpr u a e) hint) | (CmmHinted e hint) <- es
(from cmm/CmmOpt.hs) Note that it isn't substituting inside the 'fn'
argument to CmmCallee, and it should be. This bug has been around for ages.
Cheers,
Simon
On 13/01/2011 04:34, Edward Z. Yang wrote:
With further poking, I think the new codegen is actually tickling
an existing bug in the native code generator optimizations, since
the cmmz output looks ok:
cSH:
_sQR::I32 = I32[_sRi::I32 + 3]; // CmmAssign
_sQS::I32 = I32[_sRi::I32 + 7]; // CmmAssign
_sQT::I32 = I32[_sRi::I32 + 11]; // CmmAssign
_sQU::I32 = I32[_sRi::I32 + 15]; // CmmAssign
(_sR1::I32) = call "ccall" arg hints: [`signed',
PtrHint,] result hints: []
(_sQR::I32& (-4))(_sQS::I32, _sQT::I32, _sQU::I32); // CmmUnsafeForeignCall
And the only change is that in the original code generator,
the assignment to _sQR is elided.
_cSn::I32 = I32[R1 + 7];
_cSp::I32 = I32[R1 + 11];
_cSr::I32 = I32[R1 + 15];
(_sR1::I32,) = foreign "ccall"
I32[R1 + 3]((_cSn::I32, `signed'), (_cSp::I32, PtrHint),
(_cSr::I32,))[_unsafe_call_];
I further verified that there was no problem if I used -fvia-C.
On closer inspection, the fact that _sQR is referenced nowhere
in this dump should have raised alarms (I think the register
allocater happened to assign it to the same register as
_sRi, which is why the assembly looked vaguely plausible.)
I'm still not sure where a fix might lie, but if I take another
crack at it tomorrow I will probably figure it out.
Cheers,
Edward
Excerpts from Edward Z. Yang's message of Wed Jan 12 17:10:11 -0500 2011:
I appear to have tracked down the bug for ffi021: the new
code generator doesn't appear to clear the tag bit for the
pointer to heap before:
// outOfLine should follow:
(_sR1::I32,) = foreign "ccall"
_sQR::I32((I32[_sRi::I32 + 7], `signed'),
(I32[_sRi::I32 + 11], PtrHint),
(I32[_sRi::I32 + 15],))[_unsafe_call_];
// emitReturn: Sequel: Assign
;
(gdb) disas
Dump of assembler code for function sRi_info:
=> 0x0804aa6c<+0>: mov %esi,%eax
0x0804aa6e<+2>: lea 0x0(%ebp),%ecx
0x0804aa71<+5>: cmp 0x54(%ebx),%ecx
0x0804aa74<+8>: jb 0x804aab3<sRi_info+71>
0x0804aa76<+10>: add $0x4,%ebp
0x0804aa79<+13>: add $0x8,%edi
0x0804aa7c<+16>: cmp 0x5c(%ebx),%edi
0x0804aa7f<+19>: ja 0x804aaa4<sRi_info+56>
0x0804aa81<+21>: pushl 0xf(%eax)
0x0804aa84<+24>: pushl 0xb(%eax)
0x0804aa87<+27>: pushl 0x7(%eax)
0x0804aa8a<+30>: call *%eax
The pushes to the stack properly untag eax, but then we just
call the tagged pointer, which seems pretty wrong to me. Here is
the old C--:
(_sR1::I32,) = foreign "ccall"
I32[R1 + 3]((_cSc::I32, `signed'), (_cSe::I32, PtrHint),
(_cSg::I32,))[_unsafe_call_];
Unfortunately, I can't figure out where this +3 is supposed to
be happening, so I don't have a patch. Some guidance here would
be appreciated.
Cheers,
Edward
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