On the 0x222 day of Apache Harmony Alex Astapchuk wrote: > Hi all, > > Among other things listed on the JIT Dev tasks, there is a need for > calling convention (CC) fix-up for IA-32 [1]. > > Current problems are: > > 1. The calling convention(s) used are stack-based - this adds a memory > access overhead on calls. > 2. The convention currently used for managed code neither allow to pass > float-point values on XMM registers, nor it provides callee-saved XMM > registers. > 3. FPU stack is used to return float/double values > > > Both 2) and 3) affect register allocation for float point values in a > bad manner. > Fixing even the 1) looks promising for hot vm helpers like monitor > enter/exit and resolve_interface_vtable. > > So, I'm going to implement register-based calling convention for IA-32. > > The current proposal is: > - make it possible to switch between existing and new conventions > for investigation and tuning purposes > - implement 2 calling conventions: > 1. well known standard fastcall (fisrt 2 params on ECX+EDX, the > rest is on stack) > 2. DRLVM-specific convention: which involves ECX, EDX (and may > be EAX) for integer/parameters passing and also use XMMs for > float-point parameters and produce callee-save XMMs. > > The #1 may be used to call internal C-based helpers. It may also be used > to call VM helpers where XMM callee save regs may add unnecessary > overhead on the helper itself. The example I can think of is > resolve_interface helper - preserving XMMs there looks overkill.
Alex, is there some mechanism to annotate helpers' with calling conventions that you would prefer? Or are you going to hardcode > #2 will help to speed-up managed code both call-intensive and (I hope) > FP-intesive - together with register allocator tuning. I would REALLY love to see it implemented!! It is a long-awaited performance feature. FP performance of DRLVM is poor if compared to HotSpot, and the most probable reason for that is problem-2 above. A microbenchmark would be great to have. I would be also happy to see "the whole design proposal" here in the mailing list. Is it possible? > > Any comments are welcome. > > > [1] > http://wiki.apache.org/harmony/JIT_Development_Tasks#head-bffdfbc80108641ca9a8bc29ea871c67fb3b82b9 > > > -- > Thanks, > Alex > > -- Egor Pasko
