[Windows] Add support for emitting PGO/LTO magic strings in the Windows PE debug directory

clang/lib/CodeGen/BackendUtil.cpp

@@ -525,6 +525,9 @@ static bool initTargetOptions(DiagnosticsEngine &Diags,
   Options.MCOptions.PPCUseFullRegisterNames =
       CodeGenOpts.PPCUseFullRegisterNames;
   Options.MisExpect = CodeGenOpts.MisExpect;
+  Options.MCOptions.PgoInstrumentation = CodeGenOpts.getProfileInstr() > 0;
+  Options.MCOptions.PgoUse =
+      CodeGenOpts.getProfileUse() > 0 || !CodeGenOpts.SampleProfileFile.empty();
 
   return true;
 }

clang/test/CodeGen/debug-dir-win-pe-magic-sections.c

@@ -0,0 +1,23 @@
+// This test checks if COFF file compiled with
+// -fprofile-generate has magic section ".pgi" to indicate so.
+
+// REQUIRES: x86-registered-target
+
+// RUN: %clang --target=x86_64-pc-windows -fprofile-generate %s -c -o %t_x86
+// RUN: llvm-objdump -h %t_x86 | FileCheck --check-prefix=CHECK_PGI %s
+
+// CHECK_PGI: {{.*}}.pgi{{.*}}
+
+// This test checks if COFF file contains a magic ".pgu" section to indicate that
+// it was compiled using profiling data.
+
+// RUN: llvm-profdata merge -output=%code.profdata %S/Inputs/thinlto_expect1.proftext
+// RUN: %clang --target=x86_64-pc-windows -fprofile-use=%code.profdata -c %s -o %t.obj
+// RUN: llvm-objdump -h %t.obj | FileCheck --check-prefix=CHECK_PGU %s
+
+// CHECK_PGU: {{.*}}.pgu{{.*}}
+
+int main(void) {
+
+	return 0;
+}

lld/COFF/Writer.cpp

@@ -77,6 +77,12 @@ static unsigned char dosProgram[] = {
 static_assert(sizeof(dosProgram) % 8 == 0,
               "DOSProgram size must be multiple of 8");
 
+static char ltcg[] = "LTCG";
+static char pgi[] = "PGI";
+static char pgu[] = "PGU";
+static char pgiSectionName[] = ".pgi";
+static char pguSectionName[] = ".pgu";
+
 static const int dosStubSize = sizeof(dos_header) + sizeof(dosProgram);
 static_assert(dosStubSize % 8 == 0, "DOSStub size must be multiple of 8");
 
@@ -179,6 +185,23 @@ class ExtendedDllCharacteristicsChunk : public NonSectionChunk {
   uint32_t characteristics = 0;
 };
 
+class DebugDirStringChunk : public NonSectionChunk {
+public:
+  DebugDirStringChunk(std::string str) : str(str.begin(), str.end()) {
+    while (this->str.size() % 4 != 0)
+      this->str.push_back(0);
+  }
+  size_t getSize() const override { return str.size(); }
+
+  void writeTo(uint8_t *b) const override {
+    char *p = reinterpret_cast<char *>(b);
+    auto strReverse = str;
+    std::reverse(strReverse.begin(), strReverse.end());
+    memcpy(p, strReverse.data(), strReverse.size());
+  }
+  std::vector<char> str;
+};
+
 // PartialSection represents a group of chunks that contribute to an
 // OutputSection. Collating a collection of PartialSections of same name and
 // characteristics constitutes the OutputSection.
@@ -1165,6 +1188,22 @@ void Writer::createMiscChunks() {
   llvm::TimeTraceScope timeScope("Misc chunks");
   Configuration *config = &ctx.config;
 
+  auto searchForPgoMagicSection = [this](char sectionName[]) {
+    for (auto *obj : ctx.objFileInstances) {
+      for (auto &chunk : obj->getChunks()) {
+        if (chunk->kind() == Chunk::SectionKind &&
+            chunk->getSectionName() == sectionName) {
+          return true;
+        }
+      }
+    }
+    return false;
+  };
+
+  bool writePgi = searchForPgoMagicSection(pgiSectionName);
+  bool writePgu = !writePgi && searchForPgoMagicSection(pguSectionName);
+  bool writeLTO = ctx.bitcodeFileInstances.size();
+
   for (MergeChunk *p : ctx.mergeChunkInstances) {
     if (p) {
       p->finalizeContents();
@@ -1181,7 +1220,7 @@ void Writer::createMiscChunks() {
   // Create Debug Information Chunks
   debugInfoSec = config->mingw ? buildidSec : rdataSec;
   if (config->buildIDHash != BuildIDHash::None || config->debug ||
-      config->repro || config->cetCompat) {
+      config->repro || config->cetCompat || writePgi || writePgu || writeLTO) {
     debugDirectory =
         make<DebugDirectoryChunk>(ctx, debugRecords, config->repro);
     debugDirectory->setAlignment(4);
@@ -1206,6 +1245,19 @@ void Writer::createMiscChunks() {
                                   IMAGE_DLL_CHARACTERISTICS_EX_CET_COMPAT));
   }
 
+  if (writeLTO) {
+    debugRecords.emplace_back(COFF::IMAGE_DEBUG_TYPE_POGO,
+                              make<DebugDirStringChunk>(ltcg));
+  }
+
+  if (writePgi) {
+    debugRecords.emplace_back(COFF::IMAGE_DEBUG_TYPE_POGO,
+                              make<DebugDirStringChunk>(pgi));
+  } else if (writePgu) {
+    debugRecords.emplace_back(COFF::IMAGE_DEBUG_TYPE_POGO,
+                              make<DebugDirStringChunk>(pgu));
+  }
+
   // Align and add each chunk referenced by the debug data directory.
   for (std::pair<COFF::DebugType, Chunk *> r : debugRecords) {
     r.second->setAlignment(4);

lld/test/COFF/debug_dir_magic_strings_from_section_pgi.s

@@ -0,0 +1,15 @@
+// This test checks if lld puts magic string "PGI" when an object files contains
+// .pgi section.
+
+// REQUIRES: x86
+
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-windows %s -o %t.main_x86.obj
+
+// RUN: lld-link -out:%t_x86.exe %t.main_x86.obj  -entry:entry -subsystem:console -debug:symtab
+// RUN: llvm-readobj --coff-debug-directory %t_x86.exe | FileCheck --check-prefix=CHECK_PGI %s
+// CHECK_PGI: {{.*}}IGP{{.*}}
+
+#--- main.s
+.section .pgi
+.global entry
+entry:

lld/test/COFF/debug_dir_magic_strings_from_section_pgu.s

@@ -0,0 +1,15 @@
+// This test checks if lld puts magic string "PGU" when an object files contains
+// .pgu section.
+
+// REQUIRES: x86
+
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-windows %s -o %t.main_x86.obj
+
+// RUN: lld-link -out:%t_x86.exe %t.main_x86.obj  -entry:entry -subsystem:console -debug:symtab
+// RUN: llvm-readobj --coff-debug-directory %t_x86.exe | FileCheck --check-prefix=CHECK_PGU %s
+// CHECK_PGU: {{.*}}UGP{{.*}}
+
+#--- main.s
+.section .pgu
+.global entry
+entry:

lld/test/COFF/debug_dir_magic_strings_lto.ll

@@ -0,0 +1,12 @@
+; REQUIRES: x86
+; RUN: llvm-as -o %main.obj %s
+; RUN: lld-link /out:%main.exe /entry:main  /subsystem:console %main.obj
+; RUN: llvm-readobj --coff-debug-directory %main.exe
+; CHECK: {{.*}}GCTL{{.*}}
+
+target datalayout = "e-m:w-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows"
+
+define i32 @main() {
+  ret i32 0
+}

llvm/include/llvm/MC/MCTargetOptions.h

@@ -112,6 +112,8 @@ class MCTargetOptions {
   // Whether or not to use full register names on PowerPC.
   bool PPCUseFullRegisterNames : 1;
 
+  bool PgoInstrumentation = false;
+  bool PgoUse = false;
   MCTargetOptions();
 
   /// getABIName - If this returns a non-empty string this represents the

llvm/lib/MC/WinCOFFObjectWriter.cpp

@@ -28,6 +28,7 @@
 #include "llvm/MC/MCSectionCOFF.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/MCSymbolCOFF.h"
+#include "llvm/MC/MCTargetOptions.h"
 #include "llvm/MC/MCValue.h"
 #include "llvm/MC/MCWinCOFFObjectWriter.h"
 #include "llvm/MC/StringTableBuilder.h"
@@ -981,6 +982,18 @@ static std::time_t getTime() {
 uint64_t WinCOFFWriter::writeObject(MCAssembler &Asm) {
   uint64_t StartOffset = W.OS.tell();
 
+  const auto *Options = Asm.getContext().getTargetOptions();
+
+  if (Mode != DwoOnly && Options && Options->PgoInstrumentation) {
+    auto *Section = Asm.getContext().getCOFFSection(".pgi", 0);
+    defineSection(Asm, *Section);
+  }
+
+  if (Mode != DwoOnly && Options && Options->PgoUse) {
+    auto *Section = Asm.getContext().getCOFFSection(".pgu", 0);
+    defineSection(Asm, *Section);
+  }
+
   if (Sections.size() > INT32_MAX)
     report_fatal_error(
         "PE COFF object files can't have more than 2147483647 sections");