[ELF] --build-id: replace vector<uint8_t> with unique_ptr<uint8_t[]>.…

… NFC

We can't use C++20 make_unique_for_overwrite yet.

lld/ELF/Writer.cpp

@@ -2902,15 +2902,16 @@ computeHash(llvm::MutableArrayRef<uint8_t> hashBuf,
             llvm::ArrayRef<uint8_t> data,
             std::function<void(uint8_t *dest, ArrayRef<uint8_t> arr)> hashFn) {
   std::vector<ArrayRef<uint8_t>> chunks = split(data, 1024 * 1024);
-  std::vector<uint8_t> hashes(chunks.size() * hashBuf.size());
+  const size_t hashesSize = chunks.size() * hashBuf.size();
+  std::unique_ptr<uint8_t[]> hashes(new uint8_t[hashesSize]);
 
   // Compute hash values.
   parallelForEachN(0, chunks.size(), [&](size_t i) {
-    hashFn(hashes.data() + i * hashBuf.size(), chunks[i]);
+    hashFn(hashes.get() + i * hashBuf.size(), chunks[i]);
   });
 
   // Write to the final output buffer.
-  hashFn(hashBuf.data(), hashes);
+  hashFn(hashBuf.data(), makeArrayRef(hashes.get(), hashesSize));
 }
 
 template <class ELFT> void Writer<ELFT>::writeBuildId() {
@@ -2925,34 +2926,35 @@ template <class ELFT> void Writer<ELFT>::writeBuildId() {
 
   // Compute a hash of all sections of the output file.
   size_t hashSize = mainPart->buildId->hashSize;
-  std::vector<uint8_t> buildId(hashSize);
-  llvm::ArrayRef<uint8_t> buf{Out::bufferStart, size_t(fileSize)};
+  std::unique_ptr<uint8_t[]> buildId(new uint8_t[hashSize]);
+  MutableArrayRef<uint8_t> output(buildId.get(), hashSize);
+  llvm::ArrayRef<uint8_t> input{Out::bufferStart, size_t(fileSize)};
 
   switch (config->buildId) {
   case BuildIdKind::Fast:
-    computeHash(buildId, buf, [](uint8_t *dest, ArrayRef<uint8_t> arr) {
+    computeHash(output, input, [](uint8_t *dest, ArrayRef<uint8_t> arr) {
       write64le(dest, xxHash64(arr));
     });
     break;
   case BuildIdKind::Md5:
-    computeHash(buildId, buf, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
+    computeHash(output, input, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
       memcpy(dest, MD5::hash(arr).data(), hashSize);
     });
     break;
   case BuildIdKind::Sha1:
-    computeHash(buildId, buf, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
+    computeHash(output, input, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
       memcpy(dest, SHA1::hash(arr).data(), hashSize);
     });
     break;
   case BuildIdKind::Uuid:
-    if (auto ec = llvm::getRandomBytes(buildId.data(), hashSize))
+    if (auto ec = llvm::getRandomBytes(buildId.get(), hashSize))
       error("entropy source failure: " + ec.message());
     break;
   default:
     llvm_unreachable("unknown BuildIdKind");
   }
   for (Partition &part : partitions)
-    part.buildId->writeBuildId(buildId);
+    part.buildId->writeBuildId(output);
 }
 
 template void elf::createSyntheticSections<ELF32LE>();