[llvm] r270249 - [RegBankSelect] Look for the best mapping in greedy mode.

[Quentin Colombet via llvm-commits]

Author: qcolombet
Date: Fri May 20 13:37:33 2016
New Revision: 270249

URL: http://llvm.org/viewvc/llvm-project?rev=270249&view=rev
Log:
[RegBankSelect] Look for the best mapping in greedy mode.

The Fast mode takes the first mapping, the greedy mode loops over all
the possible mapping for an instruction and choose the cheaper one.
Test case will come with target specific code, since we currently do not
have instructions that have several mappings.

Modified:
    llvm/trunk/include/llvm/CodeGen/GlobalISel/RegBankSelect.h
    llvm/trunk/lib/CodeGen/GlobalISel/RegBankSelect.cpp

Modified: llvm/trunk/include/llvm/CodeGen/GlobalISel/RegBankSelect.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/GlobalISel/RegBankSelect.h?rev=270249&r1=270248&r2=270249&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/GlobalISel/RegBankSelect.h (original)
+++ llvm/trunk/include/llvm/CodeGen/GlobalISel/RegBankSelect.h Fri May 20 13:37:33 2016
@@ -525,6 +525,13 @@ private:
       RegBankSelect::RepairingPlacement &RepairPt,
       const iterator_range<SmallVectorImpl<unsigned>::iterator> &NewVRegs);
 
+  /// Find the best mapping for \p MI from \p PossibleMappings.
+  /// \return a reference on the best mapping in \p PossibleMappings.
+  RegisterBankInfo::InstructionMapping &
+  findBestMapping(MachineInstr &MI,
+                  RegisterBankInfo::InstructionMappings &PossibleMappings,
+                  SmallVectorImpl<RepairingPlacement> &RepairPts);
+
   /// Compute the cost of mapping \p MI with \p InstrMapping and
   /// compute the repairing placement for such mapping in \p
   /// RepairPts.

Modified: llvm/trunk/lib/CodeGen/GlobalISel/RegBankSelect.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/GlobalISel/RegBankSelect.cpp?rev=270249&r1=270248&r2=270249&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/GlobalISel/RegBankSelect.cpp (original)
+++ llvm/trunk/lib/CodeGen/GlobalISel/RegBankSelect.cpp Fri May 20 13:37:33 2016
@@ -136,6 +136,27 @@ void RegBankSelect::repairReg(
   // Legalize NewInstrs if need be.
 }
 
+RegisterBankInfo::InstructionMapping &RegBankSelect::findBestMapping(
+    MachineInstr &MI, RegisterBankInfo::InstructionMappings &PossibleMappings,
+    SmallVectorImpl<RepairingPlacement> &RepairPts) {
+
+  RegisterBankInfo::InstructionMapping *BestMapping = nullptr;
+  MappingCost Cost = MappingCost::ImpossibleCost();
+  SmallVector<RepairingPlacement, 4> LocalRepairPts;
+  for (RegisterBankInfo::InstructionMapping &CurMapping : PossibleMappings) {
+    MappingCost CurCost = computeMapping(MI, CurMapping, LocalRepairPts, &Cost);
+    if (CurCost < Cost) {
+      Cost = CurCost;
+      BestMapping = &CurMapping;
+      RepairPts.clear();
+      for (RepairingPlacement &RepairPt : LocalRepairPts)
+        RepairPts.emplace_back(std::move(RepairPt));
+    }
+  }
+  assert(BestMapping && "No suitable mapping for instruction");
+  return *BestMapping;
+}
+
 void RegBankSelect::tryAvoidingSplit(
     RegBankSelect::RepairingPlacement &RepairPt, const MachineOperand &MO,
     const RegisterBankInfo::ValueMapping &ValMapping) const {
@@ -433,22 +454,29 @@ void RegBankSelect::applyMapping(
 
 void RegBankSelect::assignInstr(MachineInstr &MI) {
   DEBUG(dbgs() << "Assign: " << MI);
-  RegisterBankInfo::InstructionMapping DefaultMapping =
-      RBI->getInstrMapping(MI);
   // Remember the repairing placement for all the operands.
   SmallVector<RepairingPlacement, 4> RepairPts;
 
-  MappingCost DefaultCost = computeMapping(MI, DefaultMapping, RepairPts);
-  (void)DefaultCost;
-  assert(DefaultCost != MappingCost::ImpossibleCost() &&
-         "Default mapping is not suited");
-
+  RegisterBankInfo::InstructionMapping BestMapping;
+  if (OptMode == RegBankSelect::Mode::Fast) {
+    BestMapping = RBI->getInstrMapping(MI);
+    MappingCost DefaultCost = computeMapping(MI, BestMapping, RepairPts);
+    (void)DefaultCost;
+    assert(DefaultCost != MappingCost::ImpossibleCost() &&
+           "Default mapping is not suited");
+  } else {
+    RegisterBankInfo::InstructionMappings PossibleMappings =
+        RBI->getInstrPossibleMappings(MI);
+    assert(!PossibleMappings.empty() &&
+           "Do not know how to map this instruction");
+    BestMapping = std::move(findBestMapping(MI, PossibleMappings, RepairPts));
+  }
   // Make sure the mapping is valid for MI.
-  assert(DefaultMapping.verify(MI) && "Invalid instruction mapping");
+  assert(BestMapping.verify(MI) && "Invalid instruction mapping");
 
-  DEBUG(dbgs() << "Mapping: " << DefaultMapping << '\n');
+  DEBUG(dbgs() << "Mapping: " << BestMapping << '\n');
 
-  applyMapping(MI, DefaultMapping, RepairPts);
+  applyMapping(MI, BestMapping, RepairPts);
 
   DEBUG(dbgs() << "Assigned: " << MI);
 }