Switch case-ranges, new approach (PR1255).

[Stepan Dyatkovskiy]

Ping. Does somebody interested in this issue? I'm working on fixing some 
test-suite tests now.

-Stepan

Stepan Dyatkovskiy wrote:
> Hello, I propose new approach to switch case-ranges
> implementation (PR1255).
>
> Don't modify SwitchInst, but implement new instruction.
>
> In this case:
> 1. We don't affect current functionality and tests.
> 2. We keep backward compatibility in natural way. If you need current
> functionality (without case ranges) just use 'switch'.
>
> Here I have attached set of patches:
>
> -- New instruction itself. It is called 'SwitchRInst'. Implementation
>     is ConstantRange based. Internally switch is represented as just an
>     array of integers. Though i-th and i+1 integer represents a range,
>     and i-th integer is linked with this-range successor. This is a
>     result of implementation discussions in IRC and ML.
>     Patch name: switchr-2013-05-07-instruction.patch
>
> -- Parser/AsmWriter patch. After this patch IR parser will
>     recognize new instruction and its syntax ('switchr' keyword will
>     be added).
>     Patch contains unit-tests.
>     Patch name: switchr-2013-05-07-parser-writer.patch
>     Requires: switchr-2013-05-07-instruction.patch
>
> -- Bitcode patch. Patch adds new instruction support
>     for .bc files with.
>     Patch contains unit-tests.
>     Patch name: switchr-2013-05-07-bitcode.patch
>     Requires: switchr-2013-05-07-instruction.patch
>              [switchr-2013-05-07-parser-writer.patch] (for unit-tests)
>
> -- "Essential passes" patch. This patch finally enables 'switchr':
>     it becomes absultely legal on LLVM level. Patch updates next passes:
>     * SelectionDAGBuilder: lowers 'switchr';
>     * IRBuilder: "Create" method;
>     * SCCP: just a stub, that marks all 'switchr' successors
>     as reachable.
>     Patch contains unit-tests.
>     Patch name: switchr-2013-05-07-essential-passes.patch
>     Requires: switchr-2013-05-07-instruction.patch
>              [switchr-2013-05-07-parser-writer.patch] (for unit-tests)
>
> -- Switch-to-SwitchR pass patch. Adds function pass that replaces
>     'switch' instructions with 'switchr'.
>     Patch name: switchr-2013-05-07-switch-to-switchr.patch
>
> -- Clang patch. Adds '-fforce-switchr' option: with this flag clang
>     will use 'switchr' instructions instead of 'switch'. Actually, it
>     inserts SwitchToSwitchR patch.
>     Patch contains unit-tests.
>     Patch name: switchr-clang-force-flag-2013-05-07.patch
>     Requires: switchr-2013-05-07-instruction.patch
>               switchr-2013-05-07-switch-to-switchr.patch
>              [switchr-2013-05-07-parser-writer.patch] (for unit-tests)
>
> Also I've attached summary LLVM patch (all-in-one).
>
> -Stepan.