[llvm-commits] [llvm] r171735 - in /llvm/trunk: include/llvm/Analysis/ include/llvm/Transforms/ lib/Analysis/ lib/CodeGen/ lib/Transforms/Scalar/ test/Transforms/LoopStrengthReduce/ test/Transforms/LoopStrengthReduce/X86/

[Andrew Trick]

On Jan 7, 2013, at 4:53 PM, Chris Lattner <clattner at apple.com> wrote:

> On Jan 7, 2013, at 6:41 AM, Chandler Carruth <chandlerc at gmail.com> wrote:
>> URL: http://llvm.org/viewvc/llvm-project?rev=171735&view=rev
>> Log:
>> Switch the SCEV expander and LoopStrengthReduce to use
>> TargetTransformInfo rather than TargetLowering, removing one of the
>> primary instances of the layering violation of Transforms depending
>> directly on Target.
> 
> This is soo great!
> 
>> be created by the backend. No longer is this true. LSR is now just
>> a normal pass and we should probably lift the creation of LSR out of
>> lib/CodeGen/Passes.cpp and into the PassManagerBuilder. =] I've not done
> 
> I'm not sure this is a good idea.  One nice thing about the current design is that "clang -emit-llvm" doesn't produce maximally target-specific code like LSR likes to produce.  We also really don't want to run LSR before LTO optimizations.

Correct me if I'm wrong. I don't think we want to run any irreversible loop optimizations that hinder subsequent loop analysis prior to LTO. In particular, vectorization and partial unrolling. Especially if a preloop is inserted for any reason.

Can we just tell the PassManagerBuilder that we're not ready to lower loops yet?

-Andy