[AsmParser] Diagnose empty symbol for .set directive

Summary: Diagnose empty symbol to avoid hitting assertion in MCContext::getOrCreateSymbol

Reviewers: eli.friedman, rengolin

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D26728

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@288390 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCParser/AsmParser.cpp

@@ -973,6 +973,9 @@ bool AsmParser::parsePrimaryExpr(const MCExpr *&Res, SMLoc &EndLoc) {
 
     // This is a symbol reference.
     StringRef SymbolName = Identifier;
+    if (SymbolName.empty())
+      return true;
+
     MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
 
     // Lookup the symbol variant if used.

test/MC/AsmParser/equ.s

@@ -5,5 +5,6 @@
 .set	a, 1
 .equ	a, 2
 .equiv	a, 3
+.set  b, ""
 // CHECK: error: redefinition of 'a'
-
+// CHECK: error: missing expression in '.set' directive