[MC] Move the instruction latency computation from TargetSchedModel t…

…o MCSchedModel.

The goal is to make the latency information accessible through the MCSchedModel
interface. This is particularly important for tools like llvm-mca that only have
access to the MCSchedModel API.

This partially fixes PR36676.
No functional change intended.

Differential Revision: https://reviews.llvm.org/D44383

llvm-svn: 327406

llvm/include/llvm/MC/MCSchedule.h

@@ -21,6 +21,7 @@
 namespace llvm {
 
 struct InstrItinerary;
+class MCSubtargetInfo;
 
 /// Define a kind of processor resource that will be modeled by the scheduler.
 struct MCProcResourceDesc {
@@ -226,6 +227,10 @@ struct MCSchedModel {
     return &SchedClassTable[SchedClassIdx];
   }
 
+  /// Returns the latency value for the scheduling class.
+  static int computeInstrLatency(const MCSubtargetInfo &STI,
+                                 const MCSchedClassDesc &SCDesc);
+
   /// Returns the default initialized model.
   static const MCSchedModel &GetDefaultSchedModel() { return Default; }
   static const MCSchedModel Default;

llvm/lib/CodeGen/TargetSchedule.cpp

@@ -257,15 +257,7 @@ unsigned TargetSchedModel::computeOperandLatency(
 
 unsigned
 TargetSchedModel::computeInstrLatency(const MCSchedClassDesc &SCDesc) const {
-  unsigned Latency = 0;
-  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, capLatency(WLEntry->Cycles));
-  }
-  return Latency;
+  return capLatency(MCSchedModel::computeInstrLatency(*STI, SCDesc));
 }
 
 unsigned TargetSchedModel::computeInstrLatency(unsigned Opcode) const {

llvm/lib/MC/MCSchedule.cpp

@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/MC/MCSchedule.h"
+#include "llvm/MC/MCSubtargetInfo.h"
 #include <type_traits>
 
 using namespace llvm;
@@ -32,3 +33,19 @@ const MCSchedModel MCSchedModel::Default = {DefaultIssueWidth,
                                             0,
                                             0,
                                             nullptr};
+
+int MCSchedModel::computeInstrLatency(const MCSubtargetInfo &STI,
+                                      const MCSchedClassDesc &SCDesc) {
+  int Latency = 0;
+  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);
+    // Early exit if we found an invalid latency.
+    if (WLEntry->Cycles < 0)
+      return WLEntry->Cycles;
+    Latency = std::max(Latency, static_cast<int>(WLEntry->Cycles));
+  }
+  return Latency;
+}