1 files changed, 24 insertions, 0 deletions
diff --git a/lib/CodeGen/TargetSchedule.cpp b/lib/CodeGen/TargetSchedule.cpp
index 6e7cccce42..cf9d059492 100644
--- a/lib/CodeGen/TargetSchedule.cpp
+++ b/lib/CodeGen/TargetSchedule.cpp
@@ -146,6 +146,10 @@ unsigned TargetSchedModel::computeOperandLatency(
     unsigned InstrLatency = TII->getInstrLatency(&InstrItins, DefMI);
 
     // Expected latency is the max of the stage latency and itinerary props.
+    // Rather than directly querying InstrItins stage latency, we call a TII
+    // hook to allow subtargets to specialize latency. This hook is only
+    // applicable to the InstrItins model. InstrSchedModel should model all
+    // special cases without TII hooks.
     if (!FindMin)
       InstrLatency = std::max(InstrLatency,
                               TII->defaultDefLatency(&SchedModel, DefMI));
@@ -185,3 +189,23 @@ unsigned TargetSchedModel::computeOperandLatency(
 #endif
   return 1;
 }
+
+unsigned TargetSchedModel::computeInstrLatency(const MachineInstr *MI) const {
+  if (hasInstrItineraries()) {
+    // For the itinerary model, fall back to the old subtarget hook.
+    return TII->getInstrLatency(&InstrItins, MI);
+  }
+  if (hasInstrSchedModel()) {
+    unsigned Latency = 0;
+    const MCSchedClassDesc *SCDesc = resolveSchedClass(MI);
+    for (unsigned DefIdx = 0, DefEnd = SCDesc->NumWriteLatencyEntries;
+         DefIdx != DefEnd; ++DefIdx) {
+      // Lookup the definition's write latency in SubtargetInfo.
+      const MCWriteLatencyEntry *WLEntry =
+        STI->getWriteLatencyEntry(SCDesc, DefIdx);
+      Latency = std::max(Latency, WLEntry->Cycles);
+    }
+    return Latency;
+  }
+  return TII->defaultDefLatency(&SchedModel, MI);
+}