[PATCH] D125102: [RagAllocGreedy] New hook regClassPriorityTrumpsGlobalness

[Jay Foad via Phabricator via llvm-commits]

foad created this revision.
foad added reviewers: arsenm, qcolombet, qiucf.
Herald added subscribers: hiraditya, MatzeB.
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Herald added subscribers: llvm-commits, wdng.
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Add a new TargetRegisterInfo hook to allow targets to tweak the
priority of live ranges, so that AllocationPriority of the register
class will be treated as more important than whether the range is local
to a basic block or global. This is determined per-MachineFunction.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D125102

Files:
  llvm/include/llvm/CodeGen/TargetRegisterInfo.h
  llvm/lib/CodeGen/RegAllocGreedy.cpp
  llvm/lib/CodeGen/RegAllocGreedy.h


Index: llvm/lib/CodeGen/RegAllocGreedy.h
===================================================================
--- llvm/lib/CodeGen/RegAllocGreedy.h
+++ llvm/lib/CodeGen/RegAllocGreedy.h
@@ -322,6 +322,10 @@
   /// Function
   ArrayRef<uint8_t> RegCosts;
 
+  /// Flags for the live range priority calculation, determined once per
+  /// machine function.
+  bool RegClassPriorityTrumpsGlobalness;
+
 public:
   RAGreedy(const RegClassFilterFunc F = allocateAllRegClasses);
 
Index: llvm/lib/CodeGen/RegAllocGreedy.cpp
===================================================================
--- llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -305,6 +305,7 @@
     const TargetRegisterClass &RC = *MRI->getRegClass(Reg);
     bool ForceGlobal = !ReverseLocal &&
       (Size / SlotIndex::InstrDist) > (2 * RCI.getNumAllocatableRegs(&RC));
+    unsigned GlobalBit = 0;
 
     if (Stage == RS_Assign && !ForceGlobal && !LI->empty() &&
         LIS->intervalIsInOneMBB(*LI)) {
@@ -323,9 +324,13 @@
       // Allocate global and split ranges in long->short order. Long ranges that
       // don't fit should be spilled (or split) ASAP so they don't create
       // interference.  Mark a bit to prioritize global above local ranges.
-      Prio = (1u << 29) + Size;
+      Prio = Size;
+      GlobalBit = 1;
     }
-    Prio |= RC.AllocationPriority << 24;
+    if (RegClassPriorityTrumpsGlobalness)
+      Prio |= RC.AllocationPriority << 25 | GlobalBit << 24;
+    else
+      Prio |= GlobalBit << 29 | RC.AllocationPriority << 24;
 
     // Mark a higher bit to prioritize global and local above RS_Split.
     Prio |= (1u << 31);
@@ -2692,6 +2697,7 @@
   initializeCSRCost();
 
   RegCosts = TRI->getRegisterCosts(*MF);
+  RegClassPriorityTrumpsGlobalness = TRI->regClassPriorityTrumpsGlobalness(*MF);
 
   ExtraInfo.emplace();
   EvictAdvisor =
Index: llvm/include/llvm/CodeGen/TargetRegisterInfo.h
===================================================================
--- llvm/include/llvm/CodeGen/TargetRegisterInfo.h
+++ llvm/include/llvm/CodeGen/TargetRegisterInfo.h
@@ -1076,6 +1076,14 @@
     return false;
   }
 
+  /// When prioritizing live ranges in register allocation, if this hook returns
+  /// true then the AllocationPriority of the register class will be treated as
+  /// more important than whether the range is local to a basic block or global.
+  virtual bool
+  regClassPriorityTrumpsGlobalness(const MachineFunction &MF) const {
+    return false;
+  }
+
   //===--------------------------------------------------------------------===//
   /// Debug information queries.
 


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