[AArch64][AsmParser] Fix segfault on illegal fpimm.

[sdesmalen]

Summary

Floating point immediate combining a negative sign and
a hexadecimal number, e.g. #-0x0 caused the compiler to crash.

llvm/trunk/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

AArch64AsmParser::tryParseFPImm(OperandVector &Operands) {
   bool Hash = parseOptionalToken(AsmToken::Hash);
 
   // Handle negation, as that still comes through as a separate token.
   bool isNegative = parseOptionalToken(AsmToken::Minus);
 
   const AsmToken &Tok = Parser.getTok();
   if (Tok.is(AsmToken::Real) || Tok.is(AsmToken::Integer)) {
     int64_t Val;
-    if (Tok.is(AsmToken::Integer) && !isNegative && Tok.getString().startswith("0x")) {
+    if (Tok.is(AsmToken::Integer) && Tok.getString().startswith("0x")) {
       Val = Tok.getIntVal();
-      if (Val > 255 || Val < 0) {
+      if (Val > 255 || isNegative) {
         TokError("encoded floating point value out of range");
         return MatchOperand_ParseFail;
       }
     } else {
       APFloat RealVal(APFloat::IEEEdouble(), Tok.getString());
       if (isNegative)
         RealVal.changeSign();
 

llvm/trunk/test/MC/AArch64/neon-diagnostics.s

 // CHECK:ERROR: error: invalid operand for instruction
 // CHECK:ERROR:         movi v0.2d, #0xffff00ff001f00ff
 // CHECK:ERROR:                     ^
 //----------------------------------------------------------------------
 // Vector Floating Point Move Immediate
 //----------------------------------------------------------------------
         // invalid vector type (2s, 4s, 2d)
          fmov v0.4h, #1.0
+         // invalid immediate (negative hexadecimal encoding)
+         fmov v0.4s, #-0x0
 
 // CHECK:ERROR: error: invalid operand for instruction
 // CHECK:ERROR:         fmov v0.4h, #1.0
 // CHECK:ERROR:              ^
+// CHECK-ERROR: error: encoded floating point value out of range
+// CHECK-ERROR:         fmov v0.4s, #-0x0
+// CHECK-ERROR:                     ^
 
 //----------------------------------------------------------------------
 // Vector Move -  register
 //----------------------------------------------------------------------
       // invalid vector type (8b, 16b)
       mov v0.2s, v31.8b
 // CHECK:ERROR: error: invalid operand for instruction
 // CHECK:ERROR:         mov v0.2s, v31.8b