[ARM] Error for invalid shift in memory operand

[olista01]

Summary

Report a diagnostic when we fail to parse a shift in a memory operand because the shift type is not an identifier. Without this, we were silently ignoring the whole instruction.

[rengolin]

LGTM. Thanks!

lib/Target/ARM/AsmParser/ARMAsmParser.cpp

 ///   rrx
 /// return true if it parses a shift otherwise it returns false.
 bool ARMAsmParser::parseMemRegOffsetShift(ARM_AM::ShiftOpc &St,
                                           unsigned &Amount) {
   MCAsmParser &Parser = getParser();
   SMLoc Loc = Parser.getTok().getLoc();
   const AsmToken &Tok = Parser.getTok();
   if (Tok.isNot(AsmToken::Identifier))
-    return true;
+    return Error(Loc, "illegal shift operator");
   StringRef ShiftName = Tok.getString();
   if (ShiftName == "lsl" || ShiftName == "LSL" ||
       ShiftName == "asl" || ShiftName == "ASL")
     St = ARM_AM::lsl;
   else if (ShiftName == "lsr" || ShiftName == "LSR")
     St = ARM_AM::lsr;
   else if (ShiftName == "asr" || ShiftName == "ASR")
     St = ARM_AM::asr;

test/MC/ARM/diagnostics.s

@ CHECK-ERRORS:         adc r4, r5, r6, ror #32
         pld r4, [r5, r6, lsl #32]
         str r4, [r5], r6, lsr #-1
         ldr r4, [r5, r6, lsr #33]
         pld r4, [r5, r6, asr #-1]
         str r4, [r5, r6, asr #33]
         ldr r4, [r5, r6, ror #-1]
         pld r4, [r5, r6, ror #32]
         pld r4, [r5, r6, rrx #0]
+        ldr r4, [r5, r6, not_a_shift]
 
 @ CHECK-ERRORS: error: shift amount must be an immediate
 @ CHECK-ERRORS:         str r1, [r2, r3, lsl #invalid]
 @ CHECK-ERRORS:                              ^
 @ CHECK-ERRORS: error: immediate shift value out of range
 @ CHECK-ERRORS:         ldr r4, [r5], r6, lsl #-1
 @ CHECK-ERRORS:                              ^
 @ CHECK-ERRORS: error: immediate shift value out of range

 @ CHECK-ERRORS:                              ^
 @ CHECK-ERRORS: error: immediate shift value out of range
 @ CHECK-ERRORS:         ldr r4, [r5, r6, ror #-1]
 @ CHECK-ERRORS:                              ^
 @ CHECK-ERRORS: error: immediate shift value out of range
 @ CHECK-ERRORS:         pld r4, [r5, r6, ror #32]
 @ CHECK-ERRORS: error: ']' expected
 @ CHECK-ERRORS:         pld r4, [r5, r6, rrx #0]
+@ CHECK-ERRORS: error: illegal shift operator
+@ CHECK-ERRORS:         ldr r4, [r5, r6, not_a_shift]
         
         @ Out of range 16-bit immediate on BKPT
         bkpt #65536
 
 @ CHECK-ERRORS: error: invalid instruction, any one of the following would fix this:
 @ CHECK-ERRORS: note: operand must be an immediate in the range [0,65535]
 @ CHECK-ERRORS: note: too many operands for instruction
 @ CHECK-ERRORS:         bkpt #65536