[ARM] Remove tCPS alias which just crashed

[olista01]

Summary

This alias caused a crash when trying to print the "cps #0" instruction in a diagnostic for thumbv6 (which doesn't have that instruction).

The comment was incorrect, this instruction is UNPREDICTABLE if no flag bits are set, so I don't think it's worth keeping.

[rengolin]

LGTM, thanks!

llvm/trunk/lib/Target/ARM/ARMInstrThumb.td

 }
 
 
 // In Thumb1, "nop" is encoded as a "mov r8, r8". Technically, the bf00
 // encoding is available on ARMv6K, but we don't differentiate that finely.
 def : InstAlias<"nop", (tMOVr R8, R8, 14, 0), 0>, Requires<[IsThumb, IsThumb1Only]>;
 
 
-// For round-trip assembly/disassembly, we have to handle a CPS instruction
-// without any iflags. That's not, strictly speaking, valid syntax, but it's
-// a useful extension and assembles to defined behaviour (the insn does
-// nothing).
-def : tInstAlias<"cps$imod", (tCPS imod_op:$imod, 0)>;
-def : tInstAlias<"cps$imod", (tCPS imod_op:$imod, 0)>;
-
 // "neg" is and alias for "rsb rd, rn, #0"
 def : tInstAlias<"neg${s}${p} $Rd, $Rm",
                  (tRSB tGPR:$Rd, s_cc_out:$s, tGPR:$Rm, pred:$p)>;
 
 
 // Implied destination operand forms for shifts.
 def : tInstAlias<"lsl${s}${p} $Rdm, $imm",
              (tLSLri tGPR:$Rdm, cc_out:$s, tGPR:$Rdm, imm0_31:$imm, pred:$p)>;

llvm/trunk/test/MC/ARM/cps.s

 @ RUN: llvm-mc -triple=thumbv6t2--none-eabi -show-encoding < %s | FileCheck %s
 @ RUN: llvm-mc -triple=thumbv7a--none-eabi -show-encoding < %s | FileCheck %s
 @ RUN: llvm-mc -triple=thumbv7r--none-eabi -show-encoding < %s | FileCheck %s
 @ RUN: llvm-mc -triple=thumbv8a--none-eabi -show-encoding < %s | FileCheck %s
 @ RUN: not llvm-mc -triple=thumbv7m--none-eabi -show-encoding < %s 2>&1 | FileCheck %s --check-prefix=UNDEF
+@ RUN: not llvm-mc -triple=thumbv6--none-eabi -show-encoding < %s 2>%t | FileCheck %s --check-prefix=V6
+@ RUN: FileCheck %s < %t --check-prefix=V6-ERRORS
 
   cpsie f
   cpsie i, #3
   cps #0
 
 @ CHECK: cpsie f                         @ encoding: [0x61,0xb6]
 @ CHECK: cpsie   i, #3                   @ encoding: [0xaf,0xf3,0x43,0x85]
 @ CHECK: cps     #0                      @ encoding: [0xaf,0xf3,0x00,0x81]
 
 @ UNDEF-DAG: cpsie f                         @ encoding: [0x61,0xb6]
 @ UNDEF-DAG: instruction requires:
 @ UNDEF-DAG: error: instruction 'cps' requires effect for M-class
+
+@ V6: cpsie f                         @ encoding: [0x61,0xb6]
+@ V6-ERRORS: error: invalid instruction, any one of the following would fix this:
+@ V6-ERRORS-NEXT: cpsie i, #3
+@ V6-ERRORS: note: instruction requires: thumb2
+@ V6-ERRORS: note: instruction requires: arm-mode
+@ V6-ERRORS: note: too many operands for instruction
+@ V6-ERRORS: error: invalid instruction, any one of the following would fix this:
+@ V6-ERRORS: cps #0
+@ V6-ERRORS: note: too few operands for instruction
+@ V6-ERRORS: note: instruction requires: arm-mode
+@ V6-ERRORS: note: instruction requires: thumb2