[MCA] SchedulingInfoView: consider negative ReadAdvanceCycle and AcquireAtCycle

MR #126703:
 - Negative ReadAdvance cycles can be negative, so add ForwardingDelayCycles to Latency (computeInstrLatency).

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

@@ -175,38 +175,36 @@ 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())
     return 0;
 
   unsigned Latency = 0;
-  unsigned maxLatency = 0;
+  unsigned MaxLatency = 0;
   unsigned WriteResourceID = 0;
   unsigned DefEnd = SCDesc.NumWriteLatencyEntries;
 
   for (unsigned DefIdx = 0; DefIdx != DefEnd; ++DefIdx) {
     // 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));
-    if (maxLatency > Latency) {
+      Cycles = 0;
+    if (Cycles > Latency) {
+      MaxLatency = Cycles;
       WriteResourceID = WLEntry->WriteResourceID;
     }
-    Latency = maxLatency;
+    Latency = MaxLatency;
   }
 
   for (const MCReadAdvanceEntry &E : Entries) {
-    if (E.WriteResourceID == WriteResourceID) {
+    if (E.WriteResourceID == WriteResourceID)
       return E.Cycles;
-    }
   }
 
   llvm_unreachable("WriteResourceID not found in MCReadAdvanceEntry entries");

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);
@@ -168,10 +172,12 @@ void SchedulingInfoView::collectData(
         continue;
       const MCProcResourceDesc *MCProc =
           SM.getProcResource(Index->ProcResourceIdx);
-      if (Index->ReleaseAtCycle != 1) {
+      if (Index->ReleaseAtCycle > 1) {
         // Output ReleaseAtCycle between [] if not 1 (default)
-        TempStream << sep
-                   << format("%s[%d]", MCProc->Name, Index->ReleaseAtCycle);
+	// This is to be able to evaluate throughput.
+	// See getReciprocalThroughput in MCSchedule.cpp
+	// TODO: report AcquireAtCycle to check this scheduling info.
+        TempStream << sep << format("%s[%d]", MCProc->Name, Index->ReleaseAtCycle);
       } else {
         TempStream << sep << format("%s", MCProc->Name);
       }