[LLVMdev] Question about Value Range Propagation

[Reid Kleckner]

On Tue, Feb 22, 2011 at 6:19 AM, Duncan Sands <baldrick at free.fr> wrote:
> the big problem with Patterson's VRP is that it is expensive in terms of
> compile time.  LLVM used to have some passes (ABCD, predsimplify) that did
> this kind of thing, but they were removed essentially because their compile
> time was too great for the goodness they brought.

Any reason not to just leave them on at O3?  Based on the discussion
around your simple condition propagation pass, it seemed predsimplify
did delete dead code, but it didn't really improve generated code
performance.  O3 seems the appropriate place to put expensive
optimizations with diminishing returns.

Reid