[PATCH] D138515: [CodeGen][RegAllocFast] Map PhysReg to its current VirtReg

[Christudasan Devadasan via Phabricator via llvm-commits]

cdevadas updated this revision to Diff 477539.
cdevadas edited the summary of this revision.
cdevadas added a comment.

PhysToCurrentVirtReg should also be updated while reloading a physical register from the spill location. It happens when a RegMask (for instance, a function call) clobbers a register that is used in an instruction later in the BB. Also, at a BB entry, the LiveIn registers are reloaded. The reload point begins a new live range and it should be properly reflected in the mapping.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D138515/new/

https://reviews.llvm.org/D138515

Files:
  llvm/include/llvm/CodeGen/MachineRegisterInfo.h
  llvm/lib/CodeGen/RegAllocFast.cpp


Index: llvm/lib/CodeGen/RegAllocFast.cpp
===================================================================
--- llvm/lib/CodeGen/RegAllocFast.cpp
+++ llvm/lib/CodeGen/RegAllocFast.cpp
@@ -487,6 +487,8 @@
                           MCPhysReg PhysReg) {
   LLVM_DEBUG(dbgs() << "Reloading " << printReg(VirtReg, TRI) << " into "
                     << printReg(PhysReg, TRI) << '\n');
+  MRI->setPhysToCurrentVirtReg(VirtReg);
+
   int FI = getStackSpaceFor(VirtReg);
   const TargetRegisterClass &RC = *MRI->getRegClass(VirtReg);
   TII->loadRegFromStackSlot(*MBB, Before, PhysReg, FI, &RC, TRI);
@@ -707,6 +709,7 @@
   assert(PhysReg != 0 && "Trying to assign no register");
   LR.PhysReg = PhysReg;
   setPhysRegState(PhysReg, VirtReg);
+  MRI->setPhysToCurrentVirtReg(VirtReg);
 
   assignDanglingDebugValues(AtMI, VirtReg, PhysReg);
 }
@@ -1600,6 +1603,9 @@
     MRI->clearVirtRegs();
   }
 
+  // Clear PhysToCurrentVirtReg.
+  MRI->setPhysToCurrentVirtReg(Register());
+
   StackSlotForVirtReg.clear();
   LiveDbgValueMap.clear();
   return true;
Index: llvm/include/llvm/CodeGen/MachineRegisterInfo.h
===================================================================
--- llvm/include/llvm/CodeGen/MachineRegisterInfo.h
+++ llvm/include/llvm/CodeGen/MachineRegisterInfo.h
@@ -142,6 +142,14 @@
   /// Map generic virtual registers to their low-level type.
   VRegToTypeMap VRegToType;
 
+  /// Map a physical register into the virtual register it currently represents.
+  /// Useful for some target-hooks during the RegAllocFast to map a physical
+  /// register back to its virtual register. For instance, AMDGPU needs this
+  /// mapping inside the target spill hooks to identify the spills for certain
+  /// machine operands. This field is relevant only during RegAllocFast and will
+  /// be cleared elsewhere.
+  Register PhysToCurrentVirtReg;
+
   /// Keep track of the physical registers that are live in to the function.
   /// Live in values are typically arguments in registers.  LiveIn values are
   /// allowed to have virtual registers associated with them, stored in the
@@ -769,6 +777,9 @@
   /// type \p Ty.
   Register createGenericVirtualRegister(LLT Ty, StringRef Name = "");
 
+  void setPhysToCurrentVirtReg(Register Reg) { PhysToCurrentVirtReg = Reg; }
+  Register getPhysToCurrentVirtReg() const { return PhysToCurrentVirtReg; }
+
   /// Remove all types associated to virtual registers (after instruction
   /// selection and constraining of all generic virtual registers).
   void clearVirtRegTypes();


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