TargetSchedModel API. Implement latency lookup, disabled.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164065 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/TargetSchedule.cpp

@@ -14,6 +14,7 @@
 
 #include "llvm/CodeGen/TargetSchedule.h"
 #include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetRegisterInfo.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
 #include "llvm/Support/CommandLine.h"
 
@@ -22,6 +23,9 @@ using namespace llvm;
 static cl::opt<bool> EnableSchedModel("schedmodel", cl::Hidden, cl::init(false),
   cl::desc("Use TargetSchedModel for latency lookup"));
 
+static cl::opt<bool> EnableSchedItins("scheditins", cl::Hidden, cl::init(true),
+  cl::desc("Use InstrItineraryData for latency lookup"));
+
 void TargetSchedModel::init(const MCSchedModel &sm,
                             const TargetSubtargetInfo *sti,
                             const TargetInstrInfo *tii) {
@@ -30,3 +34,139 @@ void TargetSchedModel::init(const MCSchedModel &sm,
   TII = tii;
   STI->initInstrItins(InstrItins);
 }
+
+/// If we can determine the operand latency from the def only, without machine
+/// model or itinerary lookup, do so. Otherwise return -1.
+int TargetSchedModel::getDefLatency(const MachineInstr *DefMI,
+                                    bool FindMin) const {
+
+  // Return a latency based on the itinerary properties and defining instruction
+  // if possible. Some common subtargets don't require per-operand latency,
+  // especially for minimum latencies.
+  if (FindMin) {
+    // If MinLatency is invalid, then use the itinerary for MinLatency. If no
+    // itinerary exists either, then use single cycle latency.
+    if (SchedModel.MinLatency < 0
+        && !(EnableSchedItins && hasInstrItineraries())) {
+      return 1;
+    }
+    return SchedModel.MinLatency;
+  }
+  else if (!(EnableSchedModel && hasInstrSchedModel())
+           && !(EnableSchedItins && hasInstrItineraries())) {
+    return TII->defaultDefLatency(&SchedModel, DefMI);
+  }
+  // ...operand lookup required
+  return -1;
+}
+
+/// Return the MCSchedClassDesc for this instruction. Some SchedClasses require
+/// evaluation of predicates that depend on instruction operands or flags.
+const MCSchedClassDesc *TargetSchedModel::
+resolveSchedClass(const MachineInstr *MI) const {
+
+  // Get the definition's scheduling class descriptor from this machine model.
+  unsigned SchedClass = MI->getDesc().getSchedClass();
+  const MCSchedClassDesc *SCDesc = SchedModel.getSchedClassDesc(SchedClass);
+
+#ifndef NDEBUG
+  unsigned NIter = 0;
+#endif
+  while (SCDesc->isVariant()) {
+    assert(++NIter < 6 && "Variants are nested deeper than the magic number");
+
+    SchedClass = STI->resolveSchedClass(SchedClass, MI, this);
+    SCDesc = SchedModel.getSchedClassDesc(SchedClass);
+  }
+  return SCDesc;
+}
+
+/// Find the def index of this operand. This index maps to the machine model and
+/// is independent of use operands. Def operands may be reordered with uses or
+/// merged with uses without affecting the def index (e.g. before/after
+/// regalloc). However, an instruction's def operands must never be reordered
+/// with respect to each other.
+static unsigned findDefIdx(const MachineInstr *MI, unsigned DefOperIdx) {
+  unsigned DefIdx = 0;
+  for (unsigned i = 0; i != DefOperIdx; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (MO.isReg() && MO.isDef())
+      ++DefIdx;
+  }
+  return DefIdx;
+}
+
+/// Find the use index of this operand. This is independent of the instruction's
+/// def operands.
+static unsigned findUseIdx(const MachineInstr *MI, unsigned UseOperIdx) {
+  unsigned UseIdx = 0;
+  for (unsigned i = 0; i != UseOperIdx; ++i) {
+    const MachineOperand &MO = MI->getOperand(i);
+    if (MO.isReg() && MO.isUse())
+      ++UseIdx;
+  }
+  return UseIdx;
+}
+
+// Top-level API for clients that know the operand indices.
+unsigned TargetSchedModel::computeOperandLatency(
+  const MachineInstr *DefMI, unsigned DefOperIdx,
+  const MachineInstr *UseMI, unsigned UseOperIdx,
+  bool FindMin) const {
+
+  int DefLatency = getDefLatency(DefMI, FindMin);
+  if (DefLatency >= 0)
+    return DefLatency;
+
+  if (!FindMin && EnableSchedModel && hasInstrSchedModel()) {
+    const MCSchedClassDesc *SCDesc = resolveSchedClass(DefMI);
+    unsigned DefIdx = findDefIdx(DefMI, DefOperIdx);
+    if (DefIdx < SCDesc->NumWriteLatencyEntries) {
+
+      // Lookup the definition's write latency in SubtargetInfo.
+      const MCWriteLatencyEntry *WLEntry =
+        STI->getWriteLatencyEntry(SCDesc, DefIdx);
+      unsigned WriteID = WLEntry->WriteResourceID;
+      unsigned Latency = WLEntry->Cycles;
+      if (!UseMI)
+        return Latency;
+
+      // Lookup the use's latency adjustment in SubtargetInfo.
+      const MCSchedClassDesc *UseDesc = resolveSchedClass(UseMI);
+      if (UseDesc->NumReadAdvanceEntries == 0)
+        return Latency;
+      unsigned UseIdx = findUseIdx(UseMI, UseOperIdx);
+      return Latency - STI->getReadAdvanceCycles(UseDesc, UseIdx, WriteID);
+    }
+    // If DefIdx does not exist in the model (e.g. implicit defs), then return
+    // unit latency (defaultDefLatency may be too conservative).
+    // TODO: For unknown defs, we may want to use the subtarget's model
+    // for WAW latency here instead of 1 cycle.
+    assert((!SCDesc->isValid() || DefMI->getOperand(DefOperIdx).isImplicit()) &&
+           "DefIdx exceeds machine model def operand list");
+    return 1;
+  }
+  assert(EnableSchedItins && hasInstrItineraries() &&
+         "operand latency requires itinerary");
+
+  int OperLatency = 0;
+  if (UseMI) {
+    OperLatency =
+      TII->getOperandLatency(&InstrItins, DefMI, DefOperIdx, UseMI, UseOperIdx);
+  }
+  else {
+    unsigned DefClass = DefMI->getDesc().getSchedClass();
+    OperLatency = InstrItins.getOperandCycle(DefClass, DefOperIdx);
+  }
+  if (OperLatency >= 0)
+    return OperLatency;
+
+  // No operand latency was found.
+  unsigned InstrLatency = TII->getInstrLatency(&InstrItins, DefMI);
+
+  // Expected latency is the max of the stage latency and itinerary props.
+  if (!FindMin)
+    InstrLatency = std::max(InstrLatency,
+                            TII->defaultDefLatency(&SchedModel, DefMI));
+  return InstrLatency;
+}