[llvm] Unittests and usability for BitstreamWriter incremental flushing (PR #92983)

[Teresa Johnson via llvm-commits]

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@@ -5047,27 +5050,28 @@ void llvm::WriteBitcodeToFile(const Module &M, raw_ostream &Out,
                               bool ShouldPreserveUseListOrder,
                               const ModuleSummaryIndex *Index,
                               bool GenerateHash, ModuleHash *ModHash) {
-  SmallVector<char, 0> Buffer;
-  Buffer.reserve(256*1024);
-
-  // If this is darwin or another generic macho target, reserve space for the
-  // header.
+  auto Write = [&](BitcodeWriter &Writer) {
+    Writer.writeModule(M, ShouldPreserveUseListOrder, Index, GenerateHash,
+                       ModHash);
+    Writer.writeSymtab();
+    Writer.writeStrtab();
+  };
   Triple TT(M.getTargetTriple());
-  if (TT.isOSDarwin() || TT.isOSBinFormatMachO())
+  if (TT.isOSDarwin() || TT.isOSBinFormatMachO()) {
+    // If this is darwin or another generic macho target, reserve space for the
+    // header. Note that the header is computed *after* the output is known, so
+    // we currently expliclty use a buffer, write to it, and then subsequently
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teresajohnson wrote:

typo "expliclty"

https://github.com/llvm/llvm-project/pull/92983