[ARM, Asm] Use correct source location for register tokens

[olista01]

Summary

tryParseRegister advances the lexer, so we need to take copies of the start and end locations of the register operand before calling it.

Previously, the caret in the diagnostic pointer to the comma after the r0 operand in the test, rather than the start of the operand.

llvm/trunk/lib/Target/ARM/AsmParser/ARMAsmParser.cpp

 /// Try to parse a register name.  The token must be an Identifier when called.
 /// If it's a register, an AsmOperand is created. Another AsmOperand is created
 /// if there is a "writeback". 'true' if it's not a register.
 ///
 /// TODO this is likely to change to allow different register types and or to
 /// parse for a specific register type.
 bool ARMAsmParser::tryParseRegisterWithWriteBack(OperandVector &Operands) {
   MCAsmParser &Parser = getParser();
-  const AsmToken &RegTok = Parser.getTok();
+  SMLoc RegStartLoc = Parser.getTok().getLoc();
+  SMLoc RegEndLoc = Parser.getTok().getEndLoc();
   int RegNo = tryParseRegister();
   if (RegNo == -1)
     return true;
 
-  Operands.push_back(ARMOperand::CreateReg(RegNo, RegTok.getLoc(),
-                                           RegTok.getEndLoc()));
+  Operands.push_back(ARMOperand::CreateReg(RegNo, RegStartLoc, RegEndLoc));
 
   const AsmToken &ExclaimTok = Parser.getTok();
   if (ExclaimTok.is(AsmToken::Exclaim)) {
     Operands.push_back(ARMOperand::CreateToken(ExclaimTok.getString(),
                                                ExclaimTok.getLoc()));
     Parser.Lex(); // Eat exclaim token
     return false;
   }

llvm/trunk/test/MC/ARM/register-token-source-loc.s

+// RUN: not llvm-mc -triple armv6m--none-eabi < %s 2>&1 | FileCheck %s
+
+// Some of these CHECK lines need to uses regexes to that the amount of
+// whitespace between the start of the line and the caret is significant.
+
+  add sp, r0, #4
+// CHECK: error: invalid instruction, any one of the following would fix this:
+// CHECK: note: instruction requires: thumb2
+// CHECK: note: invalid operand for instruction
+// CHECK-NEXT: {{^  add sp, r0, #4}}
+// CHECK-NEXT: {{^          \^}}
+// CHECK: note: too many operands for instruction