[Polly] Run GVN during the cleanup

[gareevroman]

Summary

Currently, GVN can be necessary to eliminate redundant instructions in case of, for instance, GEMM and float type. This patch makes GVN be run during the cleanup.

[grosser]

LGTM

[Meinersbur]

Any reason to use NewGVN instead of (old) GVN?

I thought I had already changed the cleanup pipeline to more resemble the standard pipeline. That might still be in my devel branch and forgot to upsteam that.

[gareevroman]

In D37340#858344, @Meinersbur wrote:

Any reason to use NewGVN instead of (old) GVN?

I thought that NewGVN uses a stronger algorithm. If you think the old one is more reliable, let's use it.

I thought I had already changed the cleanup pipeline to more resemble the standard pipeline. That might still be in my devel branch and forgot to upsteam that.

I think it'd be great to upstream that.

[• dberlin]

In D37340#858527, @gareevroman wrote:

In D37340#858344, @Meinersbur wrote:

Any reason to use NewGVN instead of (old) GVN?

I thought that NewGVN uses a stronger algorithm.

It does

If you think the old one is more reliable, let's use it.

FWIW: At this point, GVN has more wrong code/etc bugs against it than NewGVN.

[grosser]

Thanks Dani. Then we should certainly go for the new GVN.

[• dberlin]

In D37340#858532, @grosser wrote:

Thanks Dani. Then we should certainly go for the new GVN.

To be fair - There are things GVN is still better at you should consider:

1. I haven't moved non-constant load/store coercion to trunk. The vast majority of cases are where the value we pull out is constant, but it is a thing gvn does better ATM. It's pretty trivial to fix if it matters, it's just not made the priority list

2. GVN catches the inverse of equalities for non-branch controlling icmps, NewGVN doesn't ATM. i have a patch coming to fix this.

3. GVN does PRE, NewGVN does not.

(NewGVN is really an analysis, and i have a patch to make it so. It has a full redundancy eliminator run after the analysis, but i haven't gotten around to implementing a partial one).

lib/CodeGen/CodegenCleanup.cpp

virtual bool doInitialization(Module &M) override {
     FPM->add(createInstructionCombiningPass());
     FPM->add(createJumpThreadingPass());
     FPM->add(createCorrelatedValuePropagationPass());
     FPM->add(createCFGSimplificationPass());
     FPM->add(createInstructionCombiningPass());
     FPM->add(createCFGSimplificationPass());
     FPM->add(createReassociatePass());
     FPM->add(createLoopRotatePass());
+    FPM->add(createNewGVNPass());
     FPM->add(createLICMPass());
     FPM->add(createLoopUnswitchPass());
     FPM->add(createCFGSimplificationPass());
     FPM->add(createInstructionCombiningPass());
     FPM->add(createIndVarSimplifyPass());
     FPM->add(createLoopIdiomPass());
     FPM->add(createLoopDeletionPass());
     FPM->add(createCFGSimplificationPass());