AMDGPU/SI: Disable PostRA scheduler with SI scheduler

[axeldavy]

Summary

When the SI scheduler is enabled, disable the PostRA scheduler.

The PostRA scheduler currently tends to worsen the scheduler.
It could be reenabled with SI scheduler when better tuned.

[arsenm]

This doesn't really make sense and is an ad-hoc bug workaround. We also need the post-RA hazard recognizer which runs as part of the post-RA scheduler

[axeldavy]

Even with the mentionned bug workaround, the performance seems slightly worse with the PostRA scheduler pass.

[arsenm]

I think there's already a flag to disable the post-RA scheduler. I think it's possible now to run the hazard recognizer separately. It would be better to just use the two switches independently rather than making one option secretly imply another

lib/Target/AMDGPU/AMDGPUSubtarget.h

void setGISelAccessor(GISelAccessor &GISel) {
     this->GISel.reset(&GISel);
   }
 
   // XXX - Why is this here if it isn't in the default pass set?
   bool enableEarlyIfConversion() const override {
     return true;
   }
 
+  // The PostRA scheduler doesn't give better results with
+  // sisched.
+  bool enablePostRAScheduler() const override {
+    return !EnableSIScheduler;
+  }
+
   void overrideSchedPolicy(MachineSchedPolicy &Policy,
                            unsigned NumRegionInstrs) const override;
 
   bool isVGPRSpillingEnabled(const Function& F) const;
 
   unsigned getMaxNumUserSGPRs() const {
     return 16;
   }