Yes, that make sense. I'll wait a bit to see if Mikhail has any more suggestions and change it to is_gc_interruptible.
On 4/12/07, Xiao-Feng Li <[EMAIL PROTECTED]> wrote:
Agree that this information better be provided by VM than JIT internals. Rana, Thanks for the quick work. A minor comment: The interface name might be better use "has_gc_safepoint" or "is_gc_interruptible" than "is_suspension_point", since the helper is a function (not a point), and "suspension" is implementation detail. Thanks, xiaofeng On 4/13/07, Rana Dasgupta <[EMAIL PROTECTED]> wrote: > Mikhail, > I extended the vm-jit interface with a function: > boolean vm_is_helper_suspension_point( VM_RT_SUPPORT f) > > and attached it to your JIRA. > > Right now it returns true for almost every helper. But you may want > to update this instead of hardcoding in the jit. At some point, we > need some analysis to determine which helpers are interruptible. > > BTW, how does the jit knows which helpers throw exceptions? > > Rana > > > > On 4/11/07, Mikhail Fursov <[EMAIL PROTECTED]> wrote: > > On 4/12/07, Rana Dasgupta <[EMAIL PROTECTED]> wrote: > > > > > > On 4/11/07, Xiao-Feng Li <[EMAIL PROTECTED]> wrote: > > > > On 4/12/07, Rana Dasgupta <[EMAIL PROTECTED]> wrote: > > > > > A silly question possibly. But other than inlined fastpaths, why not > > > > > gcm treat all helper calls as interruptible? > > > > > > > > I think this needs case by case study to decide which ones can be > > > > interruptible. In most cases, the helper is only an extension of a > > > > certain bytecode operation, which can be virtually treated as a > > > > bytecode (or part of a bytecode semantics). Normally, the safepoint > > > > can be before or after it, but not in middle of it. If we think of the > > > > stack map info, the helper itself may not stand for a formal method > > > > frame for GC or exception handling. > > > > > > This is a good way to look at helper calls. My point, however, was > > > not really that helper calls should be interruptible. But that other > > > than the fastpath for which the JIT sees the IR, why not treat the > > > calls themselves as ineligible for code motion etc. like other > > > operators with side effects? Is the cost too high? > > > Implementing the interface extension is not hard for the VM, but looks > > > like implementation dependant info passed from the VM to the JIT. > > > > > > Here is more details: > > The example of a helper that can be moved by GCM are number conversion helpers. > > 'i2d' never throws exceptions and this knowledge is hardcoded in HLO. On the > > other hand this HIR opcode is translated into LIR vm-helper call, so instead > > of simple Java opcode it becomes a > > call. I can hardcode which vm-helper call is interruptable and which is > > not on the > > JIT side, but think retrieving this information from VM is a better solution. > > Another example of uninterruptable vm-helper is > > TLS accessor. This helper is placed into the middle of the inlined > > 'alloc' helper body because 'alloc' reqires TLS access. > > Now managed<->unmanaged convertion checker in GCMap pass has hardcoded > > knowledge that TLS access will never be suspended. > > > > JET compiler uses different code then OPT and maintains special > > GC-bitmasks for object operands runtime. > > The per-call gc-mask maintainance is not free and can also be > > optimized if VM provides a method to describe which call is real > > suspension point and which is not. > > > > > > > > + Suspension and exception throwing are different attributes. SOE can be > > thrown even if method is not a suspension point. So JIT must prepare stack > > info for every call it generates to be able to unwind the frame. > > > > -- > > Mikhail Fursov > > > -- http://xiao-feng.blogspot.com
