From 00384fda3cdf9c26a513fb769618010973d106aa Mon Sep 17 00:00:00 2001
From: Ana Pazos <apazos@codeaurora.org>
Date: Sat, 25 Aug 2018 01:34:32 +0000
Subject: [PATCH] [MC, RISCV] Fixed StringRef Assertion `Index < Length &&
 "Invalid index!"'

Summary:
Handle the case IDVal is an empty string.

This bug was uncovered by a LLVM MC Assembler Protocol Buffer
Fuzzer  for the RISC-V assembly language.

Reviewers: rnk

Reviewed By: rnk

Subscribers: rnk, niravd, pcc, peter.smith, asb, grosbach, llvm-commits, bcain, kito-cheng, shiva0217, rogfer01, PkmX

Differential Revision: https://reviews.llvm.org/D50808

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340678 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/MC/MCParser/AsmParser.cpp | 2 +-
 test/Assembler/empty-string.s | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)
 create mode 100644 test/Assembler/empty-string.s

diff --git a/lib/MC/MCParser/AsmParser.cpp b/lib/MC/MCParser/AsmParser.cpp
index 501a1cccf60..0a4706ed104 100644
--- a/lib/MC/MCParser/AsmParser.cpp
+++ b/lib/MC/MCParser/AsmParser.cpp
@@ -1842,7 +1842,7 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
   // Otherwise, we have a normal instruction or directive.
 
   // Directives start with "."
-  if (IDVal[0] == '.' && IDVal != ".") {
+  if (IDVal.startswith(".") && IDVal != ".") {
     // There are several entities interested in parsing directives:
     //
     // 1. The target-specific assembly parser. Some directives are target
diff --git a/test/Assembler/empty-string.s b/test/Assembler/empty-string.s
new file mode 100644
index 00000000000..2d3d0ed15ad
--- /dev/null
+++ b/test/Assembler/empty-string.s
@@ -0,0 +1,3 @@
+// REQUIRES: riscv-registered-target
+// RUN: not llvm-mc -triple riscv32-unknown-linux-gnu < %s 2>&1 | FileCheck %s
+"" # CHECK: error: unrecognized instruction mnemonic