[Webkit-unassigned] [Bug 19457] New: Create fused opcodes for tests and conditional jumps

[bugzilla-daemon at webkit.org]

http://bugs.webkit.org/show_bug.cgi?id=19457

           Summary: Create fused opcodes for tests and conditional jumps
           Product: WebKit
           Version: 526+ (Nightly build)
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: cwzwarich at uwaterloo.ca
                CC: mjs at apple.com, ggaren at apple.com, oliver at apple.com


We have been talking about creating superinstructions for a while now. I added
some instrumentation to the VM (enable DUMP_OPCODE_STATS in Opcode.h in a debug
build to use it) in order to see which pairs of opcodes are most common. The
most common pairs are of the form (<test>, <conditional jump>), so I figured
that would be a good place to start.

The most common of these is (less, jtrue), which is 6.41% of all instruction
pairs on SunSpider. I made a patch that adds a new jless instruction, which
gives a 3.6% improvement on SunSpider.


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