[NewPM][Hexagon] Fix HexagonVectorLoopCarriedReusePass position in pipeline

[aeubanks]

Summary

In https://reviews.llvm.org/D88138 this was incorrectly added with
registerOptimizerLastEPCallback(), when it should be
registerLoopOptimizerEndEPCallback(), matching the legacy PM's
EP_LoopOptimizerEnd.

[rnk]

lgtm

llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp

278

Yep.

[quic_aankit]

@asbirlea I remember that HexagonVLCR pass has a dependency on LCSSA and LoopSimplifyPass. Is there any way we can run these passes too at LoopOptimizerEndEP? If not maybe use another EP for legacy PM? I'm not sure if the below code would run these passes in the correct order as well

PB.registerOptimizerLastEPCallback(
    [=](ModulePassManager &MPM, PassBuilder::OptimizationLevel Level) {
      LoopPassManager LPM(DebugPassManager);
      FunctionPassManager FPM(DebugPassManager);
      LPM.addPass(HexagonVectorLoopCarriedReusePass());
      FPM.addPass(LoopSimplifyPass());
      FPM.addPass(LCSSAPass());
      FPM.addPass(createFunctionToLoopPassAdaptor(std::move(LPM)));
      MPM.addPass(createModuleToFunctionPassAdaptor(std::move(FPM)));
    });

@pranavb Can you comment more on this?

[aeubanks]

In D93929#2485715, @quic_aankit wrote:

@asbirlea I remember that HexagonVLCR pass has a dependency on LCSSA and LoopSimplifyPass. Is there any way we can run these passes too at LoopOptimizerEndEP? If not maybe use another EP for legacy PM? I'm not sure if the below code would run these passes in the correct order as well

PB.registerOptimizerLastEPCallback(
    [=](ModulePassManager &MPM, PassBuilder::OptimizationLevel Level) {
      LoopPassManager LPM(DebugPassManager);
      FunctionPassManager FPM(DebugPassManager);
      LPM.addPass(HexagonVectorLoopCarriedReusePass());
      FPM.addPass(LoopSimplifyPass());
      FPM.addPass(LCSSAPass());
      FPM.addPass(createFunctionToLoopPassAdaptor(std::move(LPM)));
      MPM.addPass(createModuleToFunctionPassAdaptor(std::move(FPM)));
    });

@pranavb Can you comment more on this?

LCSSA should be preserved by all loop passes under the new PM. LCSSA and LoopSimplify are run before any loop pass: https://github.com/llvm/llvm-project/blob/8dddcc762dd98d53b9406b36e92f62502834187c/llvm/include/llvm/Transforms/Scalar/LoopPassManager.h#L406. Although I don't think passes are required preserve loop simplify form.

[quic_aankit]

In D93929#2485807, @aeubanks wrote:

In D93929#2485715, @quic_aankit wrote:

@asbirlea I remember that HexagonVLCR pass has a dependency on LCSSA and LoopSimplifyPass. Is there any way we can run these passes too at LoopOptimizerEndEP? If not maybe use another EP for legacy PM? I'm not sure if the below code would run these passes in the correct order as well

PB.registerOptimizerLastEPCallback(
    [=](ModulePassManager &MPM, PassBuilder::OptimizationLevel Level) {
      LoopPassManager LPM(DebugPassManager);
      FunctionPassManager FPM(DebugPassManager);
      LPM.addPass(HexagonVectorLoopCarriedReusePass());
      FPM.addPass(LoopSimplifyPass());
      FPM.addPass(LCSSAPass());
      FPM.addPass(createFunctionToLoopPassAdaptor(std::move(LPM)));
      MPM.addPass(createModuleToFunctionPassAdaptor(std::move(FPM)));
    });

@pranavb Can you comment more on this?

LCSSA should be preserved by all loop passes under the new PM. LCSSA and LoopSimplify are run before any loop pass: https://github.com/llvm/llvm-project/blob/8dddcc762dd98d53b9406b36e92f62502834187c/llvm/include/llvm/Transforms/Scalar/LoopPassManager.h#L406. Although I don't think passes are required preserve loop simplify form.

Got it. In that case, the patch looks good to me. Thanks!

llvm/lib/Target/Hexagon/HexagonTargetMachine.cpp

 
 void HexagonTargetMachine::adjustPassManager(PassManagerBuilder &PMB) {
   PMB.addExtension(
     PassManagerBuilder::EP_LateLoopOptimizations,
     [&](const PassManagerBuilder &, legacy::PassManagerBase &PM) {
       PM.add(createHexagonLoopIdiomPass());
     });
   PMB.addExtension(
       PassManagerBuilder::EP_LoopOptimizerEnd,
       [&](const PassManagerBuilder &, legacy::PassManagerBase &PM) {
         PM.add(createHexagonVectorLoopCarriedReuseLegacyPass());
       });
 }
 
 void HexagonTargetMachine::registerPassBuilderCallbacks(PassBuilder &PB,
                                                         bool DebugPassManager) {
   PB.registerLateLoopOptimizationsEPCallback(
       [=](LoopPassManager &LPM, PassBuilder::OptimizationLevel Level) {
         LPM.addPass(HexagonLoopIdiomRecognitionPass());
       });
-  PB.registerOptimizerLastEPCallback(
-      [=](ModulePassManager &MPM, PassBuilder::OptimizationLevel Level) {
-        LoopPassManager LPM(DebugPassManager);
-        FunctionPassManager FPM(DebugPassManager);
+  PB.registerLoopOptimizerEndEPCallback(
+      [=](LoopPassManager &LPM, PassBuilder::OptimizationLevel Level) {
         LPM.addPass(HexagonVectorLoopCarriedReusePass());
-        FPM.addPass(createFunctionToLoopPassAdaptor(std::move(LPM)));
-        MPM.addPass(createModuleToFunctionPassAdaptor(std::move(FPM)));
       });
 }
 
 TargetTransformInfo
 HexagonTargetMachine::getTargetTransformInfo(const Function &F) {
   return TargetTransformInfo(HexagonTTIImpl(this, F));
 }