[llvm-exegesis] Factor out DisassemblerHelper from the Analysis class

As part of preparing the reports, the Analysis class needs to print
machine instructions in a disassembled form. For this purpose, the class
has four fields (namely Context_, AsmInfo_, InstPrinter_ and Disasm_).
All the constructor of the Analysis class does is conditionally
initializing these four fields.

This commit factors out the logic for decoding machine code and printing
it in an assembler form into a separate DisassemblerHelper class.

~~

Huawei RRI, OS Lab

Reviewed By: courbet

Differential Revision: https://reviews.llvm.org/D147156

llvm/tools/llvm-exegesis/lib/Analysis.cpp

@@ -102,20 +102,19 @@ template <typename EscapeTag, EscapeTag Tag>
 void Analysis::writeSnippet(raw_ostream &OS, ArrayRef<uint8_t> Bytes,
                             const char *Separator) const {
   SmallVector<std::string, 3> Lines;
-  const auto &SI = State_.getSubtargetInfo();
   // Parse the asm snippet and print it.
   while (!Bytes.empty()) {
     MCInst MI;
     uint64_t MISize = 0;
-    if (!Disasm_->getInstruction(MI, MISize, Bytes, 0, nulls())) {
+    if (!DisasmHelper_->decodeInst(MI, MISize, Bytes)) {
       writeEscaped<Tag>(OS, join(Lines, Separator));
       writeEscaped<Tag>(OS, Separator);
       writeEscaped<Tag>(OS, "[error decoding asm snippet]");
       return;
     }
     SmallString<128> InstPrinterStr; // FIXME: magic number.
     raw_svector_ostream OSS(InstPrinterStr);
-    InstPrinter_->printInst(&MI, 0, "", SI, OSS);
+    DisasmHelper_->printInst(&MI, OSS);
     Bytes = Bytes.drop_front(MISize);
     Lines.emplace_back(InstPrinterStr.str().trim());
   }
@@ -163,21 +162,7 @@ Analysis::Analysis(const LLVMState &State,
   if (Clustering.getPoints().empty())
     return;
 
-  MCTargetOptions MCOptions;
-  const auto &TM = State.getTargetMachine();
-  const auto &Triple = TM.getTargetTriple();
-  AsmInfo_.reset(TM.getTarget().createMCAsmInfo(State_.getRegInfo(),
-                                                Triple.str(), MCOptions));
-  InstPrinter_.reset(TM.getTarget().createMCInstPrinter(
-      Triple, 0 /*default variant*/, *AsmInfo_, State_.getInstrInfo(),
-      State_.getRegInfo()));
-
-  Context_ = std::make_unique<MCContext>(
-      Triple, AsmInfo_.get(), &State_.getRegInfo(), &State_.getSubtargetInfo());
-  Disasm_.reset(TM.getTarget().createMCDisassembler(State_.getSubtargetInfo(),
-                                                    *Context_));
-  assert(Disasm_ && "cannot create MCDisassembler. missing call to "
-                    "InitializeXXXTargetDisassembler ?");
+  DisasmHelper_ = std::make_unique<DisassemblerHelper>(State);
 }
 
 template <>

llvm/tools/llvm-exegesis/lib/Analysis.h

@@ -15,14 +15,11 @@
 #define LLVM_TOOLS_LLVM_EXEGESIS_ANALYSIS_H
 
 #include "Clustering.h"
+#include "DisassemblerHelper.h"
 #include "SchedClassResolution.h"
-#include "llvm/MC/MCContext.h"
-#include "llvm/MC/MCDisassembler/MCDisassembler.h"
-#include "llvm/MC/MCInstPrinter.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCSubtargetInfo.h"
-#include "llvm/MC/TargetRegistry.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/raw_ostream.h"
 #include <memory>
@@ -112,10 +109,7 @@ class Analysis {
 
   const BenchmarkClustering &Clustering_;
   const LLVMState &State_;
-  std::unique_ptr<MCContext> Context_;
-  std::unique_ptr<MCAsmInfo> AsmInfo_;
-  std::unique_ptr<MCInstPrinter> InstPrinter_;
-  std::unique_ptr<MCDisassembler> Disasm_;
+  std::unique_ptr<DisassemblerHelper> DisasmHelper_;
   const double AnalysisInconsistencyEpsilonSquared_;
   const bool AnalysisDisplayUnstableOpcodes_;
 };

llvm/tools/llvm-exegesis/lib/CMakeLists.txt

@@ -51,6 +51,7 @@ add_llvm_library(LLVMExegesis
   BenchmarkRunner.cpp
   Clustering.cpp
   CodeTemplate.cpp
+  DisassemblerHelper.cpp
   Error.cpp
   LatencyBenchmarkRunner.cpp
   LlvmState.cpp

llvm/tools/llvm-exegesis/lib/DisassemblerHelper.cpp

@@ -0,0 +1,35 @@
+//===-- DisassemblerHelper.cpp ----------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "DisassemblerHelper.h"
+
+#include "llvm/MC/TargetRegistry.h"
+
+namespace llvm {
+namespace exegesis {
+
+DisassemblerHelper::DisassemblerHelper(const LLVMState &State) : State_(State) {
+  MCTargetOptions MCOptions;
+  const auto &TM = State.getTargetMachine();
+  const auto &Triple = TM.getTargetTriple();
+  AsmInfo_.reset(TM.getTarget().createMCAsmInfo(State_.getRegInfo(),
+                                                Triple.str(), MCOptions));
+  InstPrinter_.reset(TM.getTarget().createMCInstPrinter(
+      Triple, 0 /*default variant*/, *AsmInfo_, State_.getInstrInfo(),
+      State_.getRegInfo()));
+
+  Context_ = std::make_unique<MCContext>(
+      Triple, AsmInfo_.get(), &State_.getRegInfo(), &State_.getSubtargetInfo());
+  Disasm_.reset(TM.getTarget().createMCDisassembler(State_.getSubtargetInfo(),
+                                                    *Context_));
+  assert(Disasm_ && "cannot create MCDisassembler. missing call to "
+                    "InitializeXXXTargetDisassembler ?");
+}
+
+} // namespace exegesis
+} // namespace llvm

llvm/tools/llvm-exegesis/lib/DisassemblerHelper.h

@@ -0,0 +1,54 @@
+//===-- DisassemblerHelper.h ------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// Helper class for decoding machine instructions and printing them in an
+/// assembler form.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TOOLS_LLVM_EXEGESIS_DISASSEMBLER_HELPER_H
+#define LLVM_TOOLS_LLVM_EXEGESIS_DISASSEMBLER_HELPER_H
+
+#include "LlvmState.h"
+#include "llvm/MC/MCAsmInfo.h"
+#include "llvm/MC/MCContext.h"
+#include "llvm/MC/MCDisassembler/MCDisassembler.h"
+#include "llvm/MC/MCInstPrinter.h"
+
+#include <memory>
+
+namespace llvm {
+namespace exegesis {
+
+// A helper class for decoding and printing machine instructions.
+class DisassemblerHelper {
+public:
+  DisassemblerHelper(const LLVMState &State);
+
+  void printInst(const MCInst *MI, raw_ostream &OS) const {
+    const auto &STI = State_.getSubtargetInfo();
+    InstPrinter_->printInst(MI, 0, "", STI, OS);
+  }
+
+  bool decodeInst(MCInst &MI, uint64_t &MISize, ArrayRef<uint8_t> Bytes) const {
+    return Disasm_->getInstruction(MI, MISize, Bytes, 0, nulls());
+  }
+
+private:
+  const LLVMState &State_;
+  std::unique_ptr<MCContext> Context_;
+  std::unique_ptr<MCAsmInfo> AsmInfo_;
+  std::unique_ptr<MCInstPrinter> InstPrinter_;
+  std::unique_ptr<MCDisassembler> Disasm_;
+};
+
+} // namespace exegesis
+} // namespace llvm
+
+#endif // LLVM_TOOLS_LLVM_EXEGESIS_DISASSEMBLER_HELPER_H