[llvm] Reland [CGData] llvm-cgdata #89884 (PR #101461)

[Ellis Hoag via llvm-commits]

================
@@ -0,0 +1,162 @@
+//===- CodeGenDataWriter.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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains support for writing codegen data.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/CodeGenData/CodeGenDataWriter.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/EndianStream.h"
+
+#define DEBUG_TYPE "cg-data-writer"
+
+using namespace llvm;
+
+namespace llvm {
+
+/// A struct to define how the data stream should be patched.
+struct CGDataPatchItem {
+  uint64_t Pos; // Where to patch.
+  uint64_t *D;  // Pointer to an array of source data.
+  int N;        // Number of elements in \c D array.
+};
+
+// A wrapper class to abstract writer stream with support of bytes
+// back patching.
+class CGDataOStream {
+public:
+  CGDataOStream(raw_fd_ostream &FD)
+      : IsFDOStream(true), OS(FD), LE(FD, llvm::endianness::little) {}
+  CGDataOStream(raw_string_ostream &STR)
+      : IsFDOStream(false), OS(STR), LE(STR, llvm::endianness::little) {}
+
+  uint64_t tell() { return OS.tell(); }
+  void write(uint64_t V) { LE.write<uint64_t>(V); }
+  void write32(uint32_t V) { LE.write<uint32_t>(V); }
+  void write8(uint8_t V) { LE.write<uint8_t>(V); }
+
+  // \c patch can only be called when all data is written and flushed.
+  // For raw_string_ostream, the patch is done on the target string
+  // directly and it won't be reflected in the stream's internal buffer.
+  void patch(ArrayRef<CGDataPatchItem> P) {
+    using namespace support;
+
+    if (IsFDOStream) {
+      raw_fd_ostream &FDOStream = static_cast<raw_fd_ostream &>(OS);
+      const uint64_t LastPos = FDOStream.tell();
+      for (const auto &K : P) {
+        FDOStream.seek(K.Pos);
+        for (int I = 0; I < K.N; I++)
+          write(K.D[I]);
+      }
+      // Reset the stream to the last position after patching so that users
+      // don't accidentally overwrite data. This makes it consistent with
+      // the string stream below which replaces the data directly.
+      FDOStream.seek(LastPos);
+    } else {
+      raw_string_ostream &SOStream = static_cast<raw_string_ostream &>(OS);
+      std::string &Data = SOStream.str(); // with flush
+      for (const auto &K : P) {
+        for (int I = 0; I < K.N; I++) {
+          uint64_t Bytes =
+              endian::byte_swap<uint64_t, llvm::endianness::little>(K.D[I]);
+          Data.replace(K.Pos + I * sizeof(uint64_t), sizeof(uint64_t),
+                       (const char *)&Bytes, sizeof(uint64_t));
----------------
ellishg wrote:

Minor NIT:
```suggestion
                       static_cast<const char *>(&Bytes), sizeof(uint64_t));
```

https://github.com/llvm/llvm-project/pull/101461