[PATCH] D114019: [NFC][Regalloc] Split canEvictInterference|BasedOnCost

[Mircea Trofin via Phabricator via llvm-commits]

mtrofin created this revision.
mtrofin added reviewers: qcolombet, davidxl.
Herald added subscribers: hiraditya, MatzeB.
mtrofin requested review of this revision.
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Herald added a subscriber: llvm-commits.

There are 2 eviction queries. One is made by tryAssign, when it attempts to
free an interference occupying the hint of the candidate. The other is
during 'regular' interference resolution, where we scan over all
physical registers and try to see if we can evict live ranges in favor
of the candidate. We currently use the same logic in both cases, just
that the former never passes the cost to any subsequent query.
Technically, the 2 decisions could be implemented with different
policies.

This patch splits the 2.

RFC: https://lists.llvm.org/pipermail/llvm-dev/2021-November/153639.html


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D114019

Files:
  llvm/lib/CodeGen/RegAllocGreedy.cpp


Index: llvm/lib/CodeGen/RegAllocGreedy.cpp
===================================================================
--- llvm/lib/CodeGen/RegAllocGreedy.cpp
+++ llvm/lib/CodeGen/RegAllocGreedy.cpp
@@ -410,7 +410,10 @@
   void calcGapWeights(MCRegister, SmallVectorImpl<float> &);
   Register canReassign(LiveInterval &VirtReg, Register PrevReg) const;
   bool shouldEvict(LiveInterval &A, bool, LiveInterval &B, bool) const;
-  bool canEvictInterference(LiveInterval &, MCRegister, bool, EvictionCost &,
+  bool canEvictInterferenceBasedOnCost(LiveInterval &, MCRegister, bool,
+                                       EvictionCost &,
+                                       const SmallVirtRegSet &) const;
+  bool canEvictInterference(LiveInterval &, MCRegister, bool,
                             const SmallVirtRegSet &) const;
   bool canEvictInterferenceInRange(const LiveInterval &VirtReg,
                                    MCRegister PhysReg, SlotIndex Start,
@@ -780,10 +783,8 @@
     if (Order.isHint(Hint)) {
       MCRegister PhysHint = Hint.asMCReg();
       LLVM_DEBUG(dbgs() << "missed hint " << printReg(PhysHint, TRI) << '\n');
-      EvictionCost MaxCost;
-      MaxCost.setBrokenHints(1);
-      if (canEvictInterference(VirtReg, PhysHint, true, MaxCost,
-                               FixedRegisters)) {
+
+      if (canEvictInterference(VirtReg, PhysHint, true, FixedRegisters)) {
         evictInterference(VirtReg, PhysHint, NewVRegs);
         return PhysHint;
       }
@@ -864,6 +865,15 @@
   return false;
 }
 
+bool RAGreedy::canEvictInterference(
+    LiveInterval &VirtReg, MCRegister PhysReg, bool IsHint,
+    const SmallVirtRegSet &FixedRegisters) const {
+  EvictionCost MaxCost;
+  MaxCost.setBrokenHints(1);
+  return canEvictInterferenceBasedOnCost(VirtReg, PhysReg, true, MaxCost,
+                                         FixedRegisters);
+}
+
 /// canEvictInterference - Return true if all interferences between VirtReg and
 /// PhysReg can be evicted.
 ///
@@ -873,7 +883,7 @@
 /// @param MaxCost Only look for cheaper candidates and update with new cost
 ///                when returning true.
 /// @returns True when interference can be evicted cheaper than MaxCost.
-bool RAGreedy::canEvictInterference(
+bool RAGreedy::canEvictInterferenceBasedOnCost(
     LiveInterval &VirtReg, MCRegister PhysReg, bool IsHint,
     EvictionCost &MaxCost, const SmallVirtRegSet &FixedRegisters) const {
   // It is only possible to evict virtual register interference.
@@ -1150,8 +1160,8 @@
       continue;
     }
 
-    if (!canEvictInterference(VirtReg, PhysReg, false, BestCost,
-                              FixedRegisters))
+    if (!canEvictInterferenceBasedOnCost(VirtReg, PhysReg, false, BestCost,
+                                         FixedRegisters))
       continue;
 
     // Best so far.


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