[Remarks] Allow empty temporary remark files

When parsing bitstream remarks, allow external remark files to be
empty, which means there are no remarks to be parsed.

In the same way, dsymutil should not produce a remark file.

lib/Remarks/BitstreamRemarkParser.cpp

@@ -428,8 +428,13 @@ Error BitstreamRemarkParser::processExternalFilePath(
       MemoryBuffer::getFile(FullPath);
   if (std::error_code EC = BufferOrErr.getError())
     return createFileError(FullPath, EC);
+
   TmpRemarkBuffer = std::move(*BufferOrErr);
 
+  // Don't try to parse the file if it's empty.
+  if (TmpRemarkBuffer->getBufferSize() == 0)
+    return make_error<EndOfFileError>();
+
   // Create a separate parser used for parsing the separate file.
   ParserHelper = BitstreamParserHelper(TmpRemarkBuffer->getBuffer());
   // Advance and check until we can parse the meta block.

test/tools/dsymutil/Inputs/basic1.c

@@ -22,7 +22,7 @@
 
    Remarks compilation:
       for FILE in basic1.c basic2.c basic3.c; do
-         clang -gline-tables-only -c $FILE -fsave-optimization-record=bitstream -foptimization-remarks-file=/tmp/${FILE%.c}.macho.remarks.x86_64.opt.bitstream -mllvm -remarks-section -o ${FILE%.c}.macho.remarks.x86_64.o
+         clang -gline-tables-only -c $FILE -fsave-optimization-record=bitstream -foptimization-record-file=/remarks/${FILE%.c}.macho.remarks.x86_64.opt.bitstream -o ${FILE%.c}.macho.remarks.x86_64.o
       done
       clang basic1.macho.remarks.x86_64.o basic2.macho.remarks.x86_64.o basic3.macho.remarks.x86_64.o -o basic.macho.remarks.x86_64 -Wl,-dead_strip
 

test/tools/dsymutil/X86/remarks-linking-bundle-empty.test

@@ -0,0 +1,8 @@
+RUN: rm -rf %t
+RUN: mkdir -p %t
+RUN: cat %p/../Inputs/remarks/basic.macho.remarks.empty.x86_64 > %t/basic.macho.remarks.empty.x86_64
+
+RUN: dsymutil -oso-prepend-path=%p/../Inputs -remarks-prepend-path=%p/../Inputs %t/basic.macho.remarks.empty.x86_64
+
+Check that the remark file in the bundle does not exist:
+RUN: not cat %t/basic.macho.remarks.empty.x86_64.dSYM/Contents/Resources/Remarks/basic.macho.remarks.empty.x86_64 2>&1