[M68k] Fix legality declaration for MUL/DIV/REM with i8 operands

This changes the action on MUL/DIV/REM with i8 operands from "Promote"
to "Legal". The implementation of these instructions correctly handles
both i8 and i16 operands in ISel, so there is no need to promote i8 to
i16; doing so causes redundant machine instructions to be emitted.

Author: dansalvato

llvm/lib/Target/M68k/M68kISelLowering.cpp

@@ -75,7 +75,7 @@ M68kTargetLowering::M68kTargetLowering(const M68kTargetMachine &TM,
   setTruncStoreAction(MVT::i32, MVT::i8, Expand);
   setTruncStoreAction(MVT::i16, MVT::i8, Expand);
 
-  setOperationAction({ISD::MUL, ISD::SDIV, ISD::UDIV}, MVT::i8, Promote);
+  setOperationAction({ISD::MUL, ISD::SDIV, ISD::UDIV}, MVT::i8, Legal);
   setOperationAction({ISD::MUL, ISD::SDIV, ISD::UDIV}, MVT::i16, Legal);
   if (Subtarget.atLeastM68020())
     setOperationAction({ISD::MUL, ISD::SDIV, ISD::UDIV}, MVT::i32, Legal);
@@ -86,7 +86,7 @@ M68kTargetLowering::M68kTargetLowering(const M68kTargetMachine &TM,
   for (auto OP :
        {ISD::SREM, ISD::UREM, ISD::UDIVREM, ISD::SDIVREM,
         ISD::MULHS, ISD::MULHU, ISD::UMUL_LOHI, ISD::SMUL_LOHI}) {
-    setOperationAction(OP, MVT::i8, Promote);
+    setOperationAction(OP, MVT::i8, Legal);
     setOperationAction(OP, MVT::i16, Legal);
     setOperationAction(OP, MVT::i32, LibCall);
   }