[ARM] SSAT/USAT with an 'asr #32' shift should result in an undefined encoding rather than unpredictable

[bsmith]

Summary

When disassembling a SSAT/USAT with an asr #32 shift the disassembler currently returns a SoftFail, this is incorrect since such an instruction encoding is undefined without the DSP extension, (in which case it maps to a different instruction), as such the disassembler should return Fail in this case.

[jmolloy]

LGTM, thanks Bradley!

[bsmith]

Thanks, committed as r226469.

lib/Target/ARM/Disassembler/ARMDisassembler.cpp

 }
 
 static DecodeStatus DecodeT2ShifterImmOperand(MCInst &Inst, uint32_t Val,
                                               uint64_t Address,
                                               const void *Decoder) {
   DecodeStatus S = MCDisassembler::Success;
 
   // Shift of "asr #32" is not allowed in Thumb2 mode.
-  if (Val == 0x20) S = MCDisassembler::SoftFail;
+  if (Val == 0x20) S = MCDisassembler::Fail;
   Inst.addOperand(MCOperand::CreateImm(Val));
   return S;
 }
 
 static DecodeStatus DecodeSwap(MCInst &Inst, unsigned Insn,
                                uint64_t Address, const void *Decoder) {
   unsigned Rt   = fieldFromInstruction(Insn, 12, 4);
   unsigned Rt2  = fieldFromInstruction(Insn, 0,  4);

test/MC/ARM/thumb2-diagnostics.s

 @ CHECK-ERRORS: error: immediate expression for mov requires :lower16: or :upper16
 @ CHECK-ERRORS:                  ^
 
         and sp, r1, #80008000
         and pc, r1, #80008000
 @ CHECK-ERRORS: error: invalid operand for instruction
 @ CHECK-ERRORS: error: invalid operand for instruction
 
-
+ssat r0, #1, r0, asr #32
+usat r0, #1, r0, asr #32
+@ CHECK-ERRORS: error: 'asr #32' shift amount not allowed in Thumb mode
+@ CHECK-ERRORS: error: 'asr #32' shift amount not allowed in Thumb mode