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On Apr 24, 2017, at 11:00 AM, Daniel Berlin <dberlin@dberlin.org> wrote:

On Mon, Apr 24, 2017 at 10:23 AM, David Jones via llvm-dev <llvm-dev@lists.llvm.org> wrote:

How do you disable optimization for a function?

I ask because my application often compiles machine-generated code that results in pathological structures that take a long time to optimize, for little benefit. As an example, if a basic block has over a million instructions in it, then DSE can take a while, as it is O(n^2) in the number of instructions in the block.

In a lot of cases, we'd rather just fix these optimizers.

There is no reason, for example, for DSE to be N^2.

There are some that are not fixable, but ...

In my application (at least), this block is typically executed only once at run time, and is not part of a loop, so I really don't care about code quality for that block.

I am able to identify some of these conditions. I would like to tell LLVM to "not try so hard" on the pathological blocks, while keeping optimizations active for ordinary cases.

This is a use case i believe where we'd rather integrate smart limits into LLVM itself, rather than try to have people control it this way :)