On 1/24/07, Xiao-Feng Li <[EMAIL PROTECTED]> wrote:
On 1/23/07, Mikhail Fursov <[EMAIL PROTECTED]> wrote: > On 1/23/07, Xiao-Feng Li <[EMAIL PROTECTED]> wrote: > > > > > > Based on my prior experience with M2N frame work, I have the same > > feeling that compiler instrinsic might be able to deal with fast > > native call (except some corner cases where very special calling > > convention ect. is used, e.g., the native method itself is a > > hand-written asm code sequence.) > > > > Probably the compiler instrinsic semantics can be expressed with Java > > Magics, then they are just the same thing from different viewpoints. > > > > > The problem is with usual JNI calls. JIT knows nothing about M2N frames > today. Pavel wants to encode JNI stub's body with magics and do not add any > knowledge about M2N into JIT. Yes, I see his point. I wonder what is the main benefit. Is it to save the two "call" instructions?
Inlining help us not only avoid 'calls' but also give a chance to propagate parent method data into inlined methods. Sometimes even 1 extra call elimination is worth to do. For example, removal of call for monenter helper gave ~5x speedup on microtests.
So we have 2 new magics: allocateMemChunkOnStack(size) and > saveRegisters(Address, howToSave) > The problem left is EIP handling. Before making direct call JIT pushes > call's args, saves caller-save regs, so EIP changes. > When unwinding native call VM uses EIP saved in M2N frame. JIT can't find > call by this EIP and this is the problem. > I'll take a break here for a day to think more about it and read others > ideas how to deal with EIP... > Go with the compiler intrinsic approach, JIT doesn't have to compile the stub code blindly as common magics. It knows the stub is for fast native call, then it can intelligently emit code to handle EIP. Annotation or pre-generated asm sequence may help. Well, we need judge if it's worth doing with the complications.
Intrinsic approach has one drawback: there can be a lot of info in M2N frame that JIT does not want to know. With help of magics we can try to split M2N stub into 2 parts: 1) Custom part: here VM developer can link M2N into the list, save method handle, check for exceptions, do anything else VM need. 2) General part: this the intrinsic you mentioned. JIT must save registers into the specified area and generate a call. In the case 2) we can use the approach proposed by Pavel above and add the method like: callNative(Address nativeAddr, Address m2nRegSaveAddr, Params..) where m2nRegSaveAddr points to the area allocated on a stack Another problem is how to pass params (number of params? types?). Any ideas? Pavel? Xiao-Feng, did I miss something from your proposal about intrinsics? -- Mikhail Fursov
