[Webkit-unassigned] [Bug 20764] New: Proposed byte-code optimization framework

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=20764

           Summary: Proposed byte-code optimization framework
           Product: WebKit
           Version: 528+ (Nightly build)
          Platform: PC
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: Enhancement
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: zherczeg at inf.u-szeged.hu
                CC: loki at inf.u-szeged.hu, oszi at inf.u-szeged.hu, jasy at inf.u-
                    szeged.hu


Hi All,

We would like to share our ideas about a byte-code optimization framework. 

Here is a short description about it:

Purpose:
The code-block optimizer is a framework, which first parses a given code block,
builds its basic block structure, executes various optimizations, and finally,
recreates the code block again.

Invocation:
  - always invoked by nodes.cpp from FunctionBodyNode::generateCode and
ProgramNode::generateCode

Shell extensions:
  - the jsc command line tool has a new argument: -o opt[,opt[...]]  (comma
separated keywords)
    The optimizations are performed in the same order as they specified by this
argument
  - The currently supported optimization keywords:
        dce   - dead code elimination
        cfp   - constant folding and propagation

Short description of the current optimizations:
  - dead code elimination
      Now working on extended basic block level. It creates a simple def-use
system to eliminate "no side effects" instructions.
  - constant propagation
      This implementation is a general iterative solution for constant
propagation. It determines the values of all constant expressions with the help
of constans folding. Folding tries to evaulate the values of possibly constant
expressions and after that the results are propagated.

Testing:
  - The framework was tested by inserting dummy movs (mov tr0, tr0) after every
instructions. If this code passes the regression tests (jump targets are
correctly redirected) we can assume the byte code generation is OK. 
 - all optimization tests are tested individually

Major changes in the source code:
  - new files added:
     CodeBlockOptimizer.cpp and .h
     OptConstansFoldingPropagation.cpp
   - files changed:
     CodeBlock.cpp - new structures added, which are basically replicas of the
original structures, except the instruction indices are changed to byte code
pointers.
     Opcode.h - opcode flags are added to every opcode

Alternative invocation:
  - when a certain treshold is reached for a given code-block. In the latter
case, an independent thread performs the optimization, and replaces the
original block after the process is done (however, it is not included in the
proposed patch).

Any feedbacks, questions are welcome. We hope it would be useful.


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