[ARM] Relax `cpsie`/`cpsid` flag parsing.

[jroelofs]

Summary

The ARM docs suggest in examples that the flags can have either case, and there are applications in the wild that (libopencm3, for example) that expect to be able to use the uppercase spelling.

[peter.smith]

This looks like the right change to make. There isn't anything written down about case-sensitivity in unified assembly language syntax that I could find in the Arm ARM, the best I could find was in the Armasm documentation http://infocenter.arm.com/help/topic/com.arm.doc.dui0473m/dom1359731141352.html "Considerations when writing assembly language source code", which implies that all lower case or all upper case is acceptable. I think the only potential problem would be if the same letter meant two different things in upper and lower case and I can't think of any case where that happens. Both armasm and gcc seem to be fine with AIF as well as aif.

[compnerd]

Yeah, this is supposed to be case insensitive.

[jroelofs]

r313680

lib/Target/ARM/AsmParser/ARMAsmParser.cpp

     return MatchOperand_NoMatch;
   StringRef IFlagsStr = Tok.getString();
 
   // An iflags string of "none" is interpreted to mean that none of the AIF
   // bits are set.  Not a terribly useful instruction, but a valid encoding.
   unsigned IFlags = 0;
   if (IFlagsStr != "none") {
         for (int i = 0, e = IFlagsStr.size(); i != e; ++i) {
-      unsigned Flag = StringSwitch<unsigned>(IFlagsStr.substr(i, 1))
+      unsigned Flag = StringSwitch<unsigned>(IFlagsStr.substr(i, 1).lower())
         .Case("a", ARM_PROC::A)
         .Case("i", ARM_PROC::I)
         .Case("f", ARM_PROC::F)
         .Default(~0U);
 
       // If some specific iflag is already set, it means that some letter is
       // present more than once, this is not acceptable.
       if (Flag == ~0U || (IFlags & Flag))

test/MC/ARM/basic-arm-instructions.s

 @ CHECK: cmn  r0, #2                  @ encoding: [0x02,0x00,0x70,0xe3]
 @ CHECK: cmp  lr, #0                    @ encoding: [0x00,0x00,0x5e,0xe3]
 
 
 @------------------------------------------------------------------------------
 @ CPS
 @------------------------------------------------------------------------------
         cpsie  aif
+        cpsie  AIF
         cps  #15
         cpsid  if, #10
 
 @ CHECK: cpsie  aif @ encoding: [0xc0,0x01,0x08,0xf1]
+@ CHECK: cpsie  aif @ encoding: [0xc0,0x01,0x08,0xf1]
 @ CHECK: cps  #15 @ encoding: [0x0f,0x00,0x02,0xf1]
 @ CHECK: cpsid  if, #10 @ encoding: [0xca,0x00,0x0e,0xf1]
 
 
 @------------------------------------------------------------------------------
 @ DBG
 @------------------------------------------------------------------------------
         dbg #0