Add LTO section reporting tool. (#12)

* Add LTO section predicting & reporting tool.

Author: cme

llvm/tools/llvm-lto-predict-sections/CMakeLists.txt

@@ -0,0 +1,9 @@
+set(LLVM_LINK_COMPONENTS
+  Core
+  IRReader
+  Support
+  )
+
+add_llvm_tool(llvm-lto-predict-sections
+  llvm-lto-predict-sections.cpp
+  )

llvm/tools/llvm-lto-predict-sections/llvm-lto-predict-sections.cpp

@@ -0,0 +1,158 @@
+//===-- llvm-lto-predict-sections: predict symbols and sections for LTO bitcode
+//---===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This program reports the sections and symbols that may be present in final
+// link from included LTO bitcode files.
+//
+// This is a best-effort attempt to predict the sections. Inherently,
+// it can't know whether sections may be removed by the LTO
+// process. Mergeable sections can't be accounted for either.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Bitcode/BitcodeWriter.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IRReader/IRReader.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/SourceMgr.h"
+#include "llvm/Support/raw_ostream.h"
+
+using namespace llvm;
+
+static cl::OptionCategory OptionsCategory("Section Options");
+
+static cl::opt<std::string> InputFilename(cl::Positional,
+                                          cl::desc("<input bitcode file>"),
+                                          cl::init("-"),
+                                          cl::value_desc("filename"),
+                                          cl::cat(OptionsCategory));
+
+static cl::opt<bool>
+    FFunctionSections("ffunction-sections", cl::Prefix, cl::init(false),
+                      cl::desc("Place each function in its own section"),
+                      cl::cat(OptionsCategory));
+
+static cl::opt<bool>
+    FDataSections("fdata-sections", cl::Prefix, cl::init(false),
+                  cl::desc("Place each data object in its own section"),
+                  cl::cat(OptionsCategory));
+
+static cl::opt<bool> SymbolsReport("symbols", cl::Prefix, cl::init(false),
+                                   cl::desc("Report symbol names"),
+                                   cl::cat(OptionsCategory));
+
+static cl::opt<bool> SectionsReport("sections", cl::Prefix, cl::init(false),
+                                    cl::desc("Report section names"),
+                                    cl::cat(OptionsCategory));
+
+static cl::opt<bool>
+    MapReport("map", cl::Prefix, cl::init(false),
+              cl::desc("Report mapping of symbols to sections"),
+              cl::cat(OptionsCategory));
+
+std::string FunctionSectionName(Function &F) {
+  if (F.hasSection()) {
+    return F.getSection().str();
+  } else {
+    if (FFunctionSections) {
+      return ".text." + F.getName().str();
+    } else {
+      return ".text";
+    }
+  }
+}
+
+std::string GlobalSectionName(GlobalVariable &G) {
+  if (G.hasSection()) {
+    return G.getSection().str();
+  } else {
+    std::string Prefix;
+    if (G.isConstant()) {
+      Prefix = ".rodata";
+    } else {
+      if (G.hasInitializer() && !G.getInitializer()->isZeroValue()) {
+        Prefix = ".data";
+      } else {
+        Prefix = ".bss";
+      }
+    }
+    if (FDataSections) {
+      if (G.getName().str()[0] == '.') {
+        return Prefix + G.getName().str();
+      } else {
+        return Prefix + "." + G.getName().str();
+      }
+    } else {
+      return Prefix;
+    }
+  }
+}
+
+std::map<std::string, std::string> SymbolsToSectionsMap;
+std::set<std::string> SectionNames;
+std::set<std::string> SymbolNames;
+
+int main(int argc, char **argv) {
+  LLVMContext Context;
+  SMDiagnostic Err;
+  cl::HideUnrelatedOptions({&OptionsCategory});
+  cl::ParseCommandLineOptions(argc, argv, "LLVM LTO section tool\n");
+
+  std::unique_ptr<Module> M = parseIRFile(InputFilename, Err, Context);
+
+  if (!M) {
+    Err.print(argv[0], errs());
+    return 1;
+  }
+
+  auto RecordSymbol = [](std::string SymbolName, std::string SectionName) {
+    if (SectionsReport || MapReport) {
+      SectionNames.insert(SectionName);
+    }
+    if (SymbolsReport || MapReport) {
+      SymbolNames.insert(SymbolName);
+    }
+    if (MapReport) {
+      SymbolsToSectionsMap[SymbolName] = SectionName;
+    }
+  };
+
+  for (GlobalVariable &G : M->globals()) {
+    RecordSymbol(G.getName().str(), GlobalSectionName(G));
+  }
+
+  for (Function &F : M->functions()) {
+    RecordSymbol(F.getName().str(), FunctionSectionName(F));
+  }
+
+  if (SectionsReport) {
+    outs() << SectionNames.size() << " sections:\n";
+    for (auto &S : SectionNames) {
+      outs() << S << "\n";
+    }
+  }
+
+  if (SymbolsReport) {
+    outs() << SymbolNames.size() << " symbols:\n";
+    for (auto &S : SymbolNames) {
+      outs() << S << "\n";
+    }
+  }
+
+  if (MapReport) {
+    outs() << SymbolNames.size() << " symbols in " << SectionNames.size()
+           << " sections\n";
+    for (auto &M : SymbolsToSectionsMap) {
+      outs() << M.first << " " << M.second << "\n";
+    }
+  }
+
+  return 0;
+}