Re: New codegen failing test-cases

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 0x0804aa76<+10>: add $0x4,%ebp 0x0804aa79<+13>: add $0x8,%edi 0x0804aa7c<+16>: cmp 0x5c(%ebx),%edi 0x0804aa7f<+19>: ja 0x804aaa4 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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