[MCA] SchedulingInfoView: consider negative ReadAdvanceCycle and AcquireAtCycle

MR #126703:
 - Negative ReadAdvance cycles can be negative, so add ForwardingDelayCycles to Latency (computeInstrLatency).
 - Resource reservation cycles given with ReleaseAtCycle - AcquireAtCycle.

Author: JulienVillette

llvm/include/llvm/MC/MCSchedule.h

@@ -402,9 +402,9 @@ struct MCSchedModel {
   static unsigned getForwardingDelayCycles(ArrayRef<MCReadAdvanceEntry> Entries,
                                            unsigned WriteResourceIdx = 0);
 
-  /// Returns the maximum forwarding delay for maximum write latency.
-  static unsigned getForwardingDelayCycles(const MCSubtargetInfo &STI,
-                                           const MCSchedClassDesc &SCDesc);
+  /// Returns the bypass delay cycle for the maximum latency write cycle
+  static unsigned getBypassDelayCycles(const MCSubtargetInfo &STI,
+                                       const MCSchedClassDesc &SCDesc);
 
   /// Returns the default initialized model.
   static const MCSchedModel Default;

llvm/lib/MC/MCSchedule.cpp

@@ -175,9 +175,8 @@ MCSchedModel::getForwardingDelayCycles(ArrayRef<MCReadAdvanceEntry> Entries,
   return std::abs(DelayCycles);
 }
 
-unsigned
-MCSchedModel::getForwardingDelayCycles(const MCSubtargetInfo &STI,
-                                       const MCSchedClassDesc &SCDesc) {
+unsigned MCSchedModel::getBypassDelayCycles(const MCSubtargetInfo &STI,
+                                            const MCSchedClassDesc &SCDesc) {
 
   ArrayRef<MCReadAdvanceEntry> Entries = STI.getReadAdvanceEntries(SCDesc);
   if (Entries.empty())
@@ -192,11 +191,11 @@ MCSchedModel::getForwardingDelayCycles(const MCSubtargetInfo &STI,
     // Lookup the definition's write latency in SubtargetInfo.
     const MCWriteLatencyEntry *WLEntry =
         STI.getWriteLatencyEntry(&SCDesc, DefIdx);
-    // Early exit if we found an invalid latency.
-    // Consider no bypass
+    unsigned Cycles = (unsigned)WLEntry->Cycles;
+    // Invalid latency. Consider 0 cycle latency
     if (WLEntry->Cycles < 0)
-      return 0;
-    maxLatency = std::max(Latency, static_cast<unsigned>(WLEntry->Cycles));
+      Cycles = 0;
+    maxLatency = std::max(Latency, static_cast<unsigned>(Cycles));
     if (maxLatency > Latency) {
       WriteResourceID = WLEntry->WriteResourceID;
     }

llvm/tools/llvm-mca/Views/SchedulingInfoView.cpp

@@ -154,8 +154,12 @@ void SchedulingInfoView::collectData(
     IIVDEntry.OpcodeName = (std::string)MCII.getName(Inst.getOpcode());
     IIVDEntry.NumMicroOpcodes = SCDesc.NumMicroOps;
     IIVDEntry.Latency = MCSchedModel::computeInstrLatency(STI, SCDesc);
+    // Add extra latency due to delays in the forwarding data paths.
+    IIVDEntry.Latency += MCSchedModel::getForwardingDelayCycles(
+        STI.getReadAdvanceEntries(SCDesc));
+    // Get latency with bypass
     IIVDEntry.Bypass =
-        IIVDEntry.Latency - MCSchedModel::getForwardingDelayCycles(STI, SCDesc);
+        IIVDEntry.Latency - MCSchedModel::getBypassDelayCycles(STI, SCDesc);
     IIVDEntry.Throughput =
         1.0 / MCSchedModel::getReciprocalThroughput(STI, SCDesc);
     raw_string_ostream TempStream(IIVDEntry.Resources);
@@ -164,14 +168,15 @@ void SchedulingInfoView::collectData(
     const MCWriteProcResEntry *Last = STI.getWriteProcResEnd(&SCDesc);
     auto sep = "";
     for (; Index != Last; ++Index) {
-      if (!Index->ReleaseAtCycle)
+      if (!Index->ReleaseAtCycle && !Index->AcquireAtCycle)
         continue;
       const MCProcResourceDesc *MCProc =
           SM.getProcResource(Index->ProcResourceIdx);
-      if (Index->ReleaseAtCycle != 1) {
-        // Output ReleaseAtCycle between [] if not 1 (default)
-        TempStream << sep
-                   << format("%s[%d]", MCProc->Name, Index->ReleaseAtCycle);
+      unsigned ReservationCycles =
+          Index->ReleaseAtCycle - Index->AcquireAtCycle;
+      if (ReservationCycles > 1) {
+        // Output ReleaseAtCycle - AcquireAtCycle between [] if not 1 (default)
+        TempStream << sep << format("%s[%d]", MCProc->Name, ReservationCycles);
       } else {
         TempStream << sep << format("%s", MCProc->Name);
       }