[llvm-dev] Scaling to many basic blocks

Mukul Sabharwal via llvm-dev llvm-dev at lists.llvm.org
Sun Aug 23 02:24:41 PDT 2015

You can expect the register allocator to be a hotspot during compiling such
functions where I'm assuming your basic blocks also end up having millions
of variables. I've not tried this in LLVM but in other compilers I've used
it certainly has been an issue.

Since you mentioned automatic code generation which is also how I ended
up[1] in a similar situation I can tell you that 10,000 local variables or
whatever you're attempting can usually be solved by instead making it an
array of those things you were going to make individual variables.

[1] it was a protocol buffers like code generation scenario of a
schema that had thousands of fields (unrelated to each other) and I had to
sort of invent this arraying strategy to prevent compile times from
skyrocketing, that said the compiler at the time was using an n2 register
allocation algorithm.

On Saturday, August 22, 2015, Russell Wallace via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> On Sat, Aug 22, 2015 at 11:57 PM, Michael Zolotukhin <
> mzolotukhin at apple.com
> <javascript:_e(%7B%7D,'cvml','mzolotukhin at apple.com');>> wrote:
>> Hi,
>> Several passes would have troubles with such code (namely, GVN and
>> JumpThreading).
> Can you just choose not to run those particular passes? I suppose the big
> problem would be if there's a problem with the code generation and related
> stuff like instruction scheduling and register allocation - is that likely
> to be the case?

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