[ARM] ARM mov InstAlias for MOVW lacks HasV6T2

[peter.smith]

Summary

The movw instruction is only available in ARM state for V6T2 and above. The MOVi16 instruction has requirement HasV6T2 but the InstAlias for mov rd, imm where the operand is imm0_65535_expr:$imm does not. This means that movw can incorrectly be used in ARMv4 and ARMv5 by writing mov rd, 0x1234. The simple fix is to the requirement HasV6T2 to the InstAlias. Tests added to not-armv4.s.

[rengolin]

No brainer. LGTM.

[rengolin]

Committed in r269761.

lib/Target/ARM/ARMInstrInfo.td

def MOVi16 : AI1<0b1000, (outs GPR:$Rd), (ins imm0_65535_expr:$imm),
   let Inst{19-16} = imm{15-12};
   let Inst{20} = 0;
   let Inst{25} = 1;
   let DecoderMethod = "DecodeArmMOVTWInstruction";
 }
 
 def : InstAlias<"mov${p} $Rd, $imm",
                 (MOVi16 GPR:$Rd, imm0_65535_expr:$imm, pred:$p)>,
-        Requires<[IsARM]>;
+        Requires<[IsARM, HasV6T2]>;
 
 def MOVi16_ga_pcrel : PseudoInst<(outs GPR:$Rd),
                                 (ins i32imm:$addr, pclabel:$id), IIC_iMOVi, []>,
                       Sched<[WriteALU]>;
 
 let Constraints = "$src = $Rd" in {
 def MOVTi16 : AI1<0b1010, (outs GPRnopc:$Rd),
                   (ins GPR:$src, imm0_65535_expr:$imm),

test/MC/ARM/not-armv4.s

 @ RUN: not llvm-mc < %s -triple armv4-unknown-unknown -show-encoding 2>&1 | FileCheck %s
 
 @ PR18524
 @ CHECK: error: instruction requires: armv5t
 clz r4,r9
 
 @ CHECK: error: instruction requires: armv6t2
 rbit r4,r9
+
+@ CHECK: error: instruction requires: armv6t2
+movw r4,#0x1234
+@ CHECK: error: instruction requires: armv6t2
+mov  r4,#0x1234