[PATCH] D45266: [PowerPC] Add a Memory Latency Mutation to the scheduler

[Stefan Pintilie via Phabricator via llvm-commits]

stefanp created this revision.
stefanp added reviewers: kbarton, nemanjai, inouehrs, sfertile, lei, syzaara, hfinkel, echristo.

Loads and Stores that depend on the same address should be scheduled apart because we don't want a load that is waiting for a store to finish or a store that is waiting for a load to finish.

This patch depends on https://reviews.llvm.org/D45265 and so that patch would have to go in first.


https://reviews.llvm.org/D45266

Files:
  lib/Target/PowerPC/PPCSubtarget.cpp
  lib/Target/PowerPC/PPCSubtarget.h
  lib/Target/PowerPC/PPCTargetMachine.cpp


Index: lib/Target/PowerPC/PPCTargetMachine.cpp
===================================================================
--- lib/Target/PowerPC/PPCTargetMachine.cpp
+++ lib/Target/PowerPC/PPCTargetMachine.cpp
@@ -315,6 +315,20 @@
     return getTM<PPCTargetMachine>();
   }
 
+  ScheduleDAGInstrs *
+  createMachineScheduler(MachineSchedContext *C) const override {
+    ScheduleDAGMILive *DAG = createGenericSchedLive(C);
+    DAG->addMutation(llvm::make_unique<PPCSubtarget::MemLatencyMutation>());
+    return DAG;
+  }
+
+  ScheduleDAGInstrs *
+  createPostMachineScheduler(MachineSchedContext *C) const override {
+    ScheduleDAGMI *DAG = createGenericSchedPostRA(C);
+    DAG->addMutation(llvm::make_unique<PPCSubtarget::MemLatencyMutation>());
+    return DAG;
+  }
+
   void addIRPasses() override;
   bool addPreISel() override;
   bool addILPOpts() override;
Index: lib/Target/PowerPC/PPCSubtarget.h
===================================================================
--- lib/Target/PowerPC/PPCSubtarget.h
+++ lib/Target/PowerPC/PPCSubtarget.h
@@ -192,6 +192,10 @@
   /// so that we can use initializer lists for subtarget initialization.
   PPCSubtarget &initializeSubtargetDependencies(StringRef CPU, StringRef FS);
 
+  struct MemLatencyMutation : public ScheduleDAGMutation {
+    void apply(ScheduleDAGInstrs *DAG) override;
+  };
+
 private:
   void initializeEnvironment();
   void initSubtargetFeatures(StringRef CPU, StringRef FS);
Index: lib/Target/PowerPC/PPCSubtarget.cpp
===================================================================
--- lib/Target/PowerPC/PPCSubtarget.cpp
+++ lib/Target/PowerPC/PPCSubtarget.cpp
@@ -47,6 +47,25 @@
   return *this;
 }
 
+void PPCSubtarget::MemLatencyMutation::apply(ScheduleDAGInstrs *DAG) {
+  for (SUnit &SU : DAG->SUnits) {
+    // Looking for loads and stores.
+    if (SU.getInstr()->mayLoad() || SU.getInstr()->mayStore()) {
+      // If we have a memory dependency then set the latency to 4 cycles.
+      // The reason 4 is picked is because it is the best case scenario for a
+      // load when we get a cache hit.
+      for (SDep &Dep :  SU.Succs) {
+        if (Dep.isNormalMemory())
+          Dep.setLatency(4);
+      }
+      for (SDep &Dep :  SU.Preds) {
+        if (Dep.isNormalMemory())
+          Dep.setLatency(4);
+      }
+    }
+  }
+}
+
 PPCSubtarget::PPCSubtarget(const Triple &TT, const std::string &CPU,
                            const std::string &FS, const PPCTargetMachine &TM)
     : PPCGenSubtargetInfo(TT, CPU, FS), TargetTriple(TT),


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