ARM assembly parsing and encoding for SSAT instruction.

Fix the Rn register encoding for both SSAT and USAT. Update the parsing of the
shift operand to correctly handle the allowed shift types and immediate ranges
and issue meaningful diagnostics when an illegal value or shift type is
specified. Add aliases to parse an ommitted shift operand (default value of
'lsl #0').

Add tests for diagnostics and proper encoding.

llvm-svn: 135990

1 files changed, 3 insertions, 9 deletions

diff --git a/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp b/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
index 38c77d479db..07d9f8ebc77 100644
--- a/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
+++ b/llvm/lib/Target/ARM/Disassembler/ARMDisassemblerCore.cpp
@@ -1732,17 +1732,11 @@ static bool DisassembleSatFrm(MCInst &MI, unsigned Opcode, uint32_t insn,
                                                      decodeRm(insn))));
 
   if (NumOpsAdded == 4) {
-    ARM_AM::ShiftOpc Opc = (slice(insn, 6, 6) != 0 ? ARM_AM::asr : ARM_AM::lsl);
+    // Inst{6} encodes the shift type.
+    bool isASR = slice(insn, 6, 6);
     // Inst{11-7} encodes the imm5 shift amount.
     unsigned ShAmt = slice(insn, 11, 7);
-    if (ShAmt == 0) {
-      // A8.6.183.  Possible ASR shift amount of 32...
-      if (Opc == ARM_AM::asr)
-        ShAmt = 32;
-      else
-        Opc = ARM_AM::no_shift;
-    }
-    MI.addOperand(MCOperand::CreateImm(ARM_AM::getSORegOpc(Opc, ShAmt)));
+    MI.addOperand(MCOperand::CreateImm(isASR << 5 | ShAmt));
   }
   return true;
 }