[Webkit-unassigned] [Bug 151141] New: Implement table-based switches in B3/Air
bugzilla-daemon at webkit.org
bugzilla-daemon at webkit.org
Wed Nov 11 10:57:43 PST 2015
https://bugs.webkit.org/show_bug.cgi?id=151141
Bug ID: 151141
Summary: Implement table-based switches in B3/Air
Classification: Unclassified
Product: WebKit
Version: WebKit Nightly Build
Hardware: All
OS: All
Status: NEW
Severity: Normal
Priority: P2
Component: JavaScriptCore
Assignee: webkit-unassigned at lists.webkit.org
Reporter: fpizlo at apple.com
We should do this in B3::lowerMacros(). During the recursive bisecting, if we find a span of case statements that is sufficiently compact, we can optimize it down to an indirect jump. This can be represented in B3.
- The jump table can be an opaque byproduct that will eventually hold and array of CodeLocationLabels.
- Introduce a new B3 Opcode called AwesomeJump that takes a pointer to jump to and a list of BasicBlocks that are possible successors.
- AwesomeJumps can be compiled to something equivalent in Air.
- CFG simplification ignores AwesomeJumps except when they only have one successor, in which case it can turn them into a Jump.
- A late phase can tell the byproduct holding the jump table that now is a good time to get the addresses of the BasicBlocks. This will need some kind of hook into Air::generate().
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