[llvm-mca] LLVM Machine Code Analyzer.

llvm-mca is an LLVM based performance analysis tool that can be used to
statically measure the performance of code, and to help triage potential
problems with target scheduling models.

llvm-mca uses information which is already available in LLVM (e.g. scheduling
models) to statically measure the performance of machine code in a specific cpu.
Performance is measured in terms of throughput as well as processor resource
consumption. The tool currently works for processors with an out-of-order
backend, for which there is a scheduling model available in LLVM.

The main goal of this tool is not just to predict the performance of the code
when run on the target, but also help with diagnosing potential performance
issues.

Given an assembly code sequence, llvm-mca estimates the IPC (instructions per
cycle), as well as hardware resources pressure. The analysis and reporting style
were mostly inspired by the IACA tool from Intel.

This patch is related to the RFC on llvm-dev visible at this link:
http://lists.llvm.org/pipermail/llvm-dev/2018-March/121490.html

Differential Revision: https://reviews.llvm.org/D43951

llvm-svn: 326998

1 files changed, 209 insertions, 0 deletions

diff --git a/llvm/tools/llvm-mca/BackendPrinter.cpp b/llvm/tools/llvm-mca/BackendPrinter.cpp
new file mode 100644
index 00000000000..511aefa8864
--- /dev/null
+++ b/llvm/tools/llvm-mca/BackendPrinter.cpp
@@ -0,0 +1,209 @@
+//===--------------------- BackendPrinter.cpp -------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+///
+/// This file implements the BackendPrinter interface.
+///
+//===----------------------------------------------------------------------===//
+
+#include "BackendPrinter.h"
+#include "llvm/CodeGen/TargetSchedule.h"
+
+namespace mca {
+
+using namespace llvm;
+
+std::unique_ptr<ToolOutputFile>
+BackendPrinter::getOutputStream(std::string OutputFile) {
+  if (OutputFile == "")
+    OutputFile = "-";
+  std::error_code EC;
+  auto Out = llvm::make_unique<ToolOutputFile>(OutputFile, EC, sys::fs::F_None);
+  if (!EC)
+    return Out;
+  errs() << EC.message() << '\n';
+  return nullptr;
+}
+
+void BackendPrinter::printGeneralStatistics(unsigned Iterations,
+                                            unsigned Cycles,
+                                            unsigned Instructions,
+                                            unsigned DispatchWidth) const {
+  unsigned TotalInstructions = Instructions * Iterations;
+  double IPC = (double)TotalInstructions / Cycles;
+
+  std::string Buffer;
+  raw_string_ostream TempStream(Buffer);
+  TempStream << "Iterations:     " << Iterations;
+  TempStream << "\nInstructions:   " << TotalInstructions;
+  TempStream << "\nTotal Cycles:   " << Cycles;
+  TempStream << "\nDispatch Width: " << DispatchWidth;
+  TempStream << "\nIPC:            " << format("%.2f", IPC) << '\n';
+  TempStream.flush();
+  File->os() << Buffer;
+}
+
+void BackendPrinter::printRATStatistics(unsigned TotalMappings,
+                                        unsigned MaxUsedMappings) const {
+  std::string Buffer;
+  raw_string_ostream TempStream(Buffer);
+  TempStream << "\n\nRegister Alias Table:";
+  TempStream << "\nTotal number of mappings created: " << TotalMappings;
+  TempStream << "\nMax number of mappings used:      " << MaxUsedMappings
+             << '\n';
+  TempStream.flush();
+  File->os() << Buffer;
+}
+
+void BackendPrinter::printDispatchStalls(unsigned RATStalls, unsigned RCUStalls,
+                                         unsigned SCHEDQStalls,
+                                         unsigned LDQStalls, unsigned STQStalls,
+                                         unsigned DGStalls) const {
+  std::string Buffer;
+  raw_string_ostream TempStream(Buffer);
+  TempStream << "\n\nDynamic Dispatch Stall Cycles:\n";
+  TempStream << "RAT     - Register unavailable:                      "
+             << RATStalls;
+  TempStream << "\nRCU     - Retire tokens unavailable:                 "
+             << RCUStalls;
+  TempStream << "\nSCHEDQ  - Scheduler full:                            "
+             << SCHEDQStalls;
+  TempStream << "\nLQ      - Load queue full:                           "
+             << LDQStalls;
+  TempStream << "\nSQ      - Store queue full:                          "
+             << STQStalls;
+  TempStream << "\nGROUP   - Static restrictions on the dispatch group: "
+             << DGStalls;
+  TempStream << '\n';
+  TempStream.flush();
+  File->os() << Buffer;
+}
+
+void BackendPrinter::printSchedulerUsage(
+    const MCSchedModel &SM, const ArrayRef<BufferUsageEntry> &Usage) const {
+  std::string Buffer;
+  raw_string_ostream TempStream(Buffer);
+  TempStream << "\n\nScheduler's queue usage:\n";
+  const ArrayRef<uint64_t> ResourceMasks = B.getProcResourceMasks();
+  for (unsigned I = 0, E = SM.getNumProcResourceKinds(); I < E; ++I) {
+    const MCProcResourceDesc &ProcResource = *SM.getProcResource(I);
+    if (!ProcResource.BufferSize)
+      continue;
+
+    for (const BufferUsageEntry &Entry : Usage)
+      if (ResourceMasks[I] == Entry.first)
+        TempStream << ProcResource.Name << ",  " << Entry.second << '/'
+                   << ProcResource.BufferSize << '\n';
+  }
+
+  TempStream.flush();
+  File->os() << Buffer;
+}
+
+void BackendPrinter::printInstructionInfo() const {
+  std::string Buffer;
+  raw_string_ostream TempStream(Buffer);
+
+  TempStream << "\n\nInstruction Info:\n";
+  TempStream << "[1]: #uOps\n[2]: Latency\n[3]: RThroughput\n"
+             << "[4]: MayLoad\n[5]: MayStore\n[6]: HasSideEffects\n\n";
+
+  TempStream << "[1]    [2]    [3]    [4]    [5]    [6]\tInstructions:\n";
+  for (unsigned I = 0, E = B.getNumInstructions(); I < E; ++I) {
+    const MCInst &Inst = B.getMCInstFromIndex(I);
+    const InstrDesc &ID = B.getInstrDesc(Inst);
+    unsigned NumMicroOpcodes = ID.NumMicroOps;
+    unsigned Latency = ID.MaxLatency;
+    double RThroughput = B.getRThroughput(ID);
+    TempStream << ' ' << NumMicroOpcodes << "    ";
+    if (NumMicroOpcodes < 10)
+      TempStream << "  ";
+    else if (NumMicroOpcodes < 100)
+      TempStream << ' ';
+    TempStream << Latency << "   ";
+    if (Latency < 10.0)
+      TempStream << "  ";
+    else if (Latency < 100.0)
+      TempStream << ' ';
+    if (RThroughput) {
+      TempStream << format("%.2f", RThroughput) << ' ';
+      if (RThroughput < 10.0)
+        TempStream << "  ";
+      else if (RThroughput < 100.0)
+        TempStream << ' ';
+    } else {
+      TempStream << " -     ";
+    }
+    TempStream << (ID.MayLoad ? " *     " : "       ");
+    TempStream << (ID.MayStore ? " *     " : "       ");
+    TempStream << (ID.HasSideEffects ? " * " : "   ");
+    MCIP->printInst(&Inst, TempStream, "", B.getSTI());
+    TempStream << '\n';
+  }
+
+  TempStream.flush();
+  File->os() << Buffer;
+}
+
+void BackendPrinter::printReport() const {
+  assert(isFileValid());
+  unsigned Cycles = B.getNumCycles();
+  printGeneralStatistics(B.getNumIterations(), Cycles, B.getNumInstructions(),
+                         B.getDispatchWidth());
+  if (EnableVerboseOutput) {
+    printDispatchStalls(B.getNumRATStalls(), B.getNumRCUStalls(),
+                        B.getNumSQStalls(), B.getNumLDQStalls(),
+                        B.getNumSTQStalls(), B.getNumDispatchGroupStalls());
+    printRATStatistics(B.getTotalRegisterMappingsCreated(),
+                       B.getMaxUsedRegisterMappings());
+    BS->printHistograms(File->os());
+
+    std::vector<BufferUsageEntry> Usage;
+    B.getBuffersUsage(Usage);
+    printSchedulerUsage(B.getSchedModel(), Usage);
+  }
+
+  if (RPV) {
+    RPV->printResourcePressure(getOStream(), Cycles);
+    printInstructionInfo();
+  }
+
+  if (TV) {
+    TV->printTimeline(getOStream());
+    TV->printAverageWaitTimes(getOStream());
+  }
+}
+
+void BackendPrinter::addResourcePressureView() {
+  if (!RPV) {
+    RPV = llvm::make_unique<ResourcePressureView>(
+        B.getSTI(), *MCIP, B.getSourceMgr(), B.getProcResourceMasks());
+    B.addEventListener(RPV.get());
+  }
+}
+
+void BackendPrinter::addTimelineView(unsigned MaxIterations,
+                                     unsigned MaxCycles) {
+  if (!TV) {
+    TV = llvm::make_unique<TimelineView>(B.getSTI(), *MCIP, B.getSourceMgr(),
+                                         MaxIterations, MaxCycles);
+    B.addEventListener(TV.get());
+  }
+}
+
+void BackendPrinter::initialize(std::string OutputFileName) {
+  File = getOutputStream(OutputFileName);
+  MCIP->setPrintImmHex(false);
+  if (EnableVerboseOutput) {
+    BS = llvm::make_unique<BackendStatistics>();
+    B.addEventListener(BS.get());
+  }
+}
+
+} // namespace mca.