[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, 176 insertions, 0 deletions

diff --git a/llvm/tools/llvm-mca/ResourcePressureView.cpp b/llvm/tools/llvm-mca/ResourcePressureView.cpp
new file mode 100644
index 00000000000..1dd15e0bbd0
--- /dev/null
+++ b/llvm/tools/llvm-mca/ResourcePressureView.cpp
@@ -0,0 +1,176 @@
+//===--------------------- ResourcePressureView.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 methods in the ResourcePressureView interface.
+///
+//===----------------------------------------------------------------------===//
+
+#include "ResourcePressureView.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace mca {
+
+using namespace llvm;
+
+void ResourcePressureView::initialize(
+    const ArrayRef<uint64_t> ProcResourceMasks) {
+  // Populate the map of resource descriptors.
+  unsigned R2VIndex = 0;
+  const MCSchedModel &SM = STI.getSchedModel();
+  for (unsigned I = 0, E = SM.getNumProcResourceKinds(); I < E; ++I) {
+    const MCProcResourceDesc &ProcResource = *SM.getProcResource(I);
+    unsigned NumUnits = ProcResource.NumUnits;
+    // Skip groups and invalid resources with zero units.
+    if (ProcResource.SubUnitsIdxBegin || !NumUnits)
+      continue;
+
+    uint64_t ResourceMask = ProcResourceMasks[I];
+    Resource2VecIndex.insert(
+        std::pair<uint64_t, unsigned>(ResourceMask, R2VIndex));
+    R2VIndex += ProcResource.NumUnits;
+  }
+
+  NumResourceUnits = R2VIndex;
+  ResourceUsage.resize(NumResourceUnits * (Source.size() + 1));
+  std::fill(ResourceUsage.begin(), ResourceUsage.end(), 0);
+}
+
+void ResourcePressureView::onInstructionIssued(
+    unsigned Index, const ArrayRef<std::pair<ResourceRef, unsigned>> &Used) {
+  unsigned SourceIdx = Index % Source.size();
+  for (const std::pair<ResourceRef, unsigned> &Use : Used) {
+    const ResourceRef &RR = Use.first;
+    assert(Resource2VecIndex.find(RR.first) != Resource2VecIndex.end());
+    unsigned R2VIndex = Resource2VecIndex[RR.first];
+    R2VIndex += countTrailingZeros(RR.second);
+    ResourceUsage[R2VIndex + NumResourceUnits * SourceIdx] += Use.second;
+    ResourceUsage[R2VIndex + NumResourceUnits * Source.size()] += Use.second;
+  }
+}
+
+static void printColumnNames(raw_string_ostream &OS, const MCSchedModel &SM) {
+  for (unsigned I = 1, ResourceIndex = 0, E = SM.getNumProcResourceKinds();
+       I < E; ++I) {
+    const MCProcResourceDesc &ProcResource = *SM.getProcResource(I);
+    unsigned NumUnits = ProcResource.NumUnits;
+    // Skip groups and invalid resources with zero units.
+    if (ProcResource.SubUnitsIdxBegin || !NumUnits)
+      continue;
+
+    if (NumUnits == 1) {
+      OS << '[' << ResourceIndex << ']';
+      if (ResourceIndex < 10)
+        OS << "    ";
+      else
+        OS << "   ";
+      ResourceIndex++;
+      continue;
+    }
+
+    for (unsigned J = 0; J < NumUnits; ++J) {
+      OS << "[" << ResourceIndex << '.' << J << ']';
+      if (ResourceIndex < 10)
+        OS << "  ";
+      else
+        OS << ' ';
+    }
+    ResourceIndex++;
+  }
+}
+
+void ResourcePressureView::printResourcePressurePerIteration(
+    raw_ostream &OS, unsigned Executions) const {
+  std::string Buffer;
+  raw_string_ostream TempStream(Buffer);
+
+  TempStream << "\n\nResources:\n";
+  const MCSchedModel &SM = STI.getSchedModel();
+  for (unsigned I = 1, ResourceIndex = 0, E = SM.getNumProcResourceKinds();
+       I < E; ++I) {
+    const MCProcResourceDesc &ProcResource = *SM.getProcResource(I);
+    unsigned NumUnits = ProcResource.NumUnits;
+    // Skip groups and invalid resources with zero units.
+    if (ProcResource.SubUnitsIdxBegin || !NumUnits)
+      continue;
+
+    for (unsigned J = 0; J < NumUnits; ++J) {
+      TempStream << '[' << ResourceIndex;
+      if (NumUnits > 1)
+        TempStream << '.' << J;
+      TempStream << "] - " << ProcResource.Name << '\n';
+    }
+
+    ResourceIndex++;
+  }
+
+  TempStream << "\n\nResource pressure per iteration:\n";
+  printColumnNames(TempStream, SM);
+  TempStream << '\n';
+
+  for (unsigned I = 0; I < NumResourceUnits; ++I) {
+    unsigned Usage = ResourceUsage[I + Source.size() * NumResourceUnits];
+    if (!Usage) {
+      TempStream << " -     ";
+      continue;
+    }
+
+    double Pressure = (double)Usage / Executions;
+    TempStream << format("%.2f", Pressure);
+    if (Pressure < 10.0)
+      TempStream << "   ";
+    else if (Pressure < 100.0)
+      TempStream << "  ";
+    else
+      TempStream << ' ';
+  }
+
+  TempStream.flush();
+  OS << Buffer;
+}
+
+void ResourcePressureView::printResourcePressurePerInstruction(
+    raw_ostream &OS, unsigned Executions) const {
+  std::string Buffer;
+  raw_string_ostream TempStream(Buffer);
+
+  TempStream << "\n\nResource pressure by instruction:\n";
+  printColumnNames(TempStream, STI.getSchedModel());
+  TempStream << "\tInstructions:\n";
+
+  for (unsigned I = 0, E = Source.size(); I < E; ++I) {
+    for (unsigned J = 0; J < NumResourceUnits; ++J) {
+      unsigned Usage = ResourceUsage[J + I * NumResourceUnits];
+      if (Usage == 0) {
+        TempStream << " -     ";
+      } else {
+        double Pressure = (double)Usage / Executions;
+        if (Pressure < 0.005) {
+          TempStream << " -     ";
+        } else {
+          TempStream << format("%.2f", Pressure);
+          if (Pressure < 10.0)
+            TempStream << "   ";
+          else if (Pressure < 100.0)
+            TempStream << "  ";
+          else
+            TempStream << ' ';
+        }
+      }
+    }
+
+    MCIP.printInst(&Source.getMCInstFromIndex(I), TempStream, "", STI);
+    TempStream << '\n';
+    TempStream.flush();
+    OS << Buffer;
+    Buffer = "";
+  }
+}
+
+} // namespace mca