[llvm-dev] Improved jump-threading in LLVM for finite state automata

[Eli Friedman via llvm-dev]

Nobody is currently working on this, as far as I know.  If you're interested in looking into it, I'll try to answer any questions.

-Eli

From: llvm-dev <llvm-dev-bounces at lists.llvm.org> On Behalf Of Phipps, Alan via llvm-dev
Sent: Wednesday, September 23, 2020 7:34 AM
To: llvm-dev at lists.llvm.org
Subject: [EXT] [llvm-dev] Improved jump-threading in LLVM for finite state automata

It is my understanding that the implementation for jump-threading in LLVM is not presently able to effectively optimize code containing a state-machine implemented using a loop + switch.  This is the case, for example, with the Coremark benchmark function core_state_transition().  Bug 42313 was filed to address this in 2019:

https://bugs.llvm.org/show_bug.cgi?id=42313

It appears that GCC improved support for jump threading in 2015 along the same lines:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54742

Is anyone aware of any plan to do improve LLVM jump-threading along the same lines for LLVM?

Thanks!

Alan Phipps

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