[PATCH] D29835: Correct register pressure calculation in presence of subregs

[Matthias Braun via Phabricator via llvm-commits]

MatzeB added a comment.

The current implementation will miscalculate the PressureDiff objects. Could you revert this until we can further investigate and fix this.



================
Comment at: llvm/trunk/include/llvm/Target/TargetRegisterInfo.h:723-724
 
+  /// Get the weight in units of pressure for a sub register of this register
+  /// unit given a lane mask.
+  virtual unsigned getRegUnitWeight(const MachineRegisterInfo &MRI,
----------------
This description makes no sense like that: Register units have no subregisters.


================
Comment at: llvm/trunk/lib/CodeGen/MachineScheduler.cpp:1088
         PressureDiff &PDiff = getPressureDiff(&SU);
-        PDiff.addPressureChange(Reg, Decrement, &MRI);
+        PDiff.addPressureChange(P, Decrement, &MRI);
         DEBUG(
----------------
The LiveUses array here only contains register that have become live or completely dead, you do not get updates of some lanes getting added/remove at the moment. So the calculations for the pressure diffs will be out of sync when you do them at lane granularity like this.


Repository:
  rL LLVM

https://reviews.llvm.org/D29835