Nirav Dave d73d6a2ee6 [MC] Fix compiler crash in AsmParser::Lex
When an empty comment is present in an assembly file, the compiler will crash because it checks the first character for '\n' or '\r'.
The fix consists of also checking if the string is empty before accessing the *front* method of the StringRef.
A test is included for the x86 target, but this issue is reproducible with other targets as well.

Patch by Alexandru Guduleasa!

Reviewers: niravd, grosbach, llvm-commits

Reviewed By: niravd

Differential Revision: https://reviews.llvm.org/D33993

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305077 91177308-0d34-0410-b5e6-96231b3b80d8
2017-06-09 14:04:03 +00:00
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