[llvm][support] Add LDBG macro. (llvm#143704)

Add macro that mirror a common usage of logging to output .This makes it easy to have
streaming log like behavior while still using the base debug logging.

I also wanted to avoid inventing a full logging library here while enabling others to change the sink without too much pain, so put it in its own header (this also avoids making Debug depend on raw_ostream beyond forward reference). The should allow a consistent dev experience without fixing the sink too much.

---------

Co-authored-by: Mehdi Amini <[email protected]>

Author: jpienaar

llvm/include/llvm/Support/DebugLog.h

@@ -0,0 +1,68 @@
+//===- llvm/Support/DebugLog.h - Logging like debug output ------*- 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
+//
+//===----------------------------------------------------------------------===//
+// This file contains macros for logging like debug output. It builds upon the
+// support in Debug.h but provides a utility function for common debug output
+// style.
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_DEBUGLOG_H
+#define LLVM_SUPPORT_DEBUGLOG_H
+
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace llvm {
+#ifndef NDEBUG
+
+// Output with given inputs and trailing newline. E.g.,
+//   LDBG() << "Bitset contains: " << Bitset;
+// is equivalent to
+//   LLVM_DEBUG(dbgs() << DEBUG_TYPE << " [" << __FILE__ << ":" << __LINE__
+//              << "] " << "Bitset contains: " << Bitset << "\n");
+#define LDBG() DEBUGLOG_WITH_STREAM_AND_TYPE(llvm::dbgs(), DEBUG_TYPE)
+
+#define DEBUGLOG_WITH_STREAM_AND_TYPE(STREAM, TYPE)                            \
+  for (bool _c = (::llvm::DebugFlag && ::llvm::isCurrentDebugType(TYPE)); _c;  \
+       _c = false)                                                             \
+  ::llvm::impl::LogWithNewline(TYPE, __FILE__, __LINE__, (STREAM))
+
+namespace impl {
+class LogWithNewline {
+public:
+  LogWithNewline(const char *debug_type, const char *file, int line,
+                 raw_ostream &os)
+      : os(os) {
+    if (debug_type)
+      os << debug_type << " ";
+    os << "[" << file << ":" << line << "] ";
+  }
+  ~LogWithNewline() { os << '\n'; }
+  template <typename T> raw_ostream &operator<<(const T &t) && {
+    return os << t;
+  }
+
+  // Prevent copying, as this class manages newline responsibility and is
+  // intended for use as a temporary.
+  LogWithNewline(const LogWithNewline &) = delete;
+  LogWithNewline &operator=(const LogWithNewline &) = delete;
+  LogWithNewline &operator=(LogWithNewline &&) = delete;
+
+private:
+  raw_ostream &os;
+};
+} // end namespace impl
+#else
+// As others in Debug, When compiling without assertions, the -debug-* options
+// and all inputs too LDBG() are ignored.
+#define LDBG()                                                                 \
+  for (bool _c = false; _c; _c = false)                                        \
+  ::llvm::nulls()
+#endif
+} // end namespace llvm
+
+#endif // LLVM_SUPPORT_DEBUGLOG_H

llvm/unittests/Support/CMakeLists.txt

@@ -31,6 +31,7 @@ add_llvm_unittest(SupportTests
   DataExtractorTest.cpp
   DebugCounterTest.cpp
   DebugTest.cpp
+  DebugLogTest.cpp
   DivisionByConstantTest.cpp
   DJBTest.cpp
   EndianStreamTest.cpp

llvm/unittests/Support/DebugLogTest.cpp

@@ -0,0 +1,77 @@
+//===- llvm/unittest/Support/DebugLogTest.cpp -----------------------------===//
+//
+// 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 "llvm/Support/DebugLog.h"
+#include "llvm/Support/raw_ostream.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+#include <string>
+using namespace llvm;
+using testing::Eq;
+using testing::HasSubstr;
+
+#ifndef NDEBUG
+TEST(DebugLogTest, Basic) {
+  llvm::DebugFlag = true;
+  static const char *DT[] = {"A", "B"};
+
+  // Clear debug types.
+  setCurrentDebugTypes(DT, 0);
+  {
+    std::string str;
+    raw_string_ostream os(str);
+    DEBUGLOG_WITH_STREAM_AND_TYPE(os, nullptr) << "NoType";
+    EXPECT_TRUE(StringRef(os.str()).starts_with('['));
+    EXPECT_TRUE(StringRef(os.str()).ends_with("NoType\n"));
+  }
+
+  setCurrentDebugTypes(DT, 2);
+  {
+    std::string str;
+    raw_string_ostream os(str);
+    DEBUGLOG_WITH_STREAM_AND_TYPE(os, "A") << "A";
+    DEBUGLOG_WITH_STREAM_AND_TYPE(os, "B") << "B";
+    EXPECT_THAT(os.str(), AllOf(HasSubstr("A\n"), HasSubstr("B\n")));
+  }
+
+  setCurrentDebugType("A");
+  {
+    std::string str;
+    raw_string_ostream os(str);
+    // Just check that the macro doesn't result in dangling else.
+    if (true)
+      DEBUGLOG_WITH_STREAM_AND_TYPE(os, "A") << "A";
+    else
+      DEBUGLOG_WITH_STREAM_AND_TYPE(os, "A") << "B";
+    DEBUGLOG_WITH_STREAM_AND_TYPE(os, "B") << "B";
+    EXPECT_THAT(os.str(), AllOf(HasSubstr("A\n"), Not(HasSubstr("B\n"))));
+
+    int count = 0;
+    auto inc = [&]() { return ++count; };
+    EXPECT_THAT(count, Eq(0));
+    DEBUGLOG_WITH_STREAM_AND_TYPE(os, "A") << inc();
+    EXPECT_THAT(count, Eq(1));
+    DEBUGLOG_WITH_STREAM_AND_TYPE(os, "B") << inc();
+    EXPECT_THAT(count, Eq(1));
+  }
+}
+#else
+TEST(DebugLogTest, Basic) {
+  // LDBG should be compiled out in NDEBUG, so just check it compiles and has
+  // no effect.
+  llvm::DebugFlag = true;
+  static const char *DT[] = {};
+  setCurrentDebugTypes(DT, 0);
+  int count = 0;
+  auto inc = [&]() { return ++count; };
+  EXPECT_THAT(count, Eq(0));
+  LDBG() << inc();
+  EXPECT_THAT(count, Eq(0));
+}
+#endif