CC: gcc@gcc.gnu.org. On 13/03/2012, at 1:48 PM, peng zhao wrote:
> Hi, Maxim, > > Thanks a lot for the help. > > Why are they called BEGIN_DATA and BE_IN_DATA? I was trying to find out > what the names stand for but failed. what do "BE" and "IN" mean in BE_IN_DATA? BE IN DATA speculation block. > My understanding is that BEGIN_DATA is for TRUE dependence that can be > speculated (or overcome) Yes. > and BE_IN_DATA is for the data dependence edge that connects the > recovery-load and the consumer of the load. Am I right? Not exactly. It is for data dependence edge the connects speculated load with its consumers that can be speculated (i.e., moved into a data speculation block) too. > > Can you also explain a little more about the concepts of DEPS_LIST and > INSN_LIST? I don't quite understand the comments in sched-int.h: /* If set, > generate links between instruction as DEPS_LIST. > Otherwise, generate usual INSN_LIST links. */ > > I am assuming that the instruction means rtx, right? which field is used > to link these rtx into DEPS_LIST or INSN_LIST? what is the purpose to have > these 2 different scenarios? > DEPS_LIST is a super-set of INSN_LIST. I kept INSN_LIST-style dependencies to avoid overhead on targets that don't need additional features of DEPS_LIST. Now that I look back at it, I should have removed INSN_LIST-style dependencies; I still hope to find time and clean that up (remove support for INSN_LIST-style dependencies). > 2. Why only speculative scheduling needs DEP_STATUS? It seems that all other > schedulers have DEP_STATUS field set to -1. But Selective scheduler needs the additional information fields that DEP_STATUS provides; other schedulers don't (ia64 speculation aside). -- Maxim Kuvyrkov > > Subject: Re: Join my network on LinkedIn > > From: maxim.kuvyr...@gmail.com > > Date: Mon, 12 Mar 2012 15:36:35 +1300 > > To: zhaop...@live.com > > > > On 12/03/2012, at 3:18 PM, Peng Zhao via LinkedIn wrote: > > > > > LinkedIn > > > Peng Zhao has indicated you are a Friend > > > Hello, Maxim, > > > Recently I started to work on GCC and I have some questions. I would > > > appreciate your input. > > > 1. what does BEGIN_DATA / BE_IN_DATA stand for? > > > 2. Why only speculative scheduling needs DEP_STATUS? > > > > Hi Zhao, > > > > First of all, it is better to write such questions to gcc@gcc.gnu.org > > mailing list, so that other developers can contribute to the answer. Please > > CC: gcc@gcc.gnu.org on any follow ups. > > > > BEGIN_DATA and BE_IN_DATA are flags that are set on dependencies, currently > > they can be set only for IA64 architecture, as it is the only one that > > supports data speculation instructions. > > > > A dependency with a BEGIN_DATA flag can be broken by making the consuming > > instruction of the dependency start a data-speculation block. The producer > > in this case is always a memory store instruction and consumer is always a > > memory load instruction. By converting the memory load instruction to data > > speculative form, the dependency can be ignored. This provides greater > > scheduling freedom if memory store (producer) and memory load (consumer) > > turn out not to be aliased at run time. > > > > BE_IN_DATA flags are set for consumers of the memory load that was > > data-speculated, i.e., it started a data-speculation block. All consumers > > of data-speculative memory load must be tracked for the case when > > speculation fails and recovery needs to be executed to preserve program > > correctness. > > > > This is a very redacted description of the data speculation optimization, > > and you need to refer my original submissions to gcc-patches@ and to IA64 > > architecture documentation. > > > > -- > > Maxim Kuvyrkov > >
