[RISCV][NFC] Simplify code.

[jacquesguan]

Summary

Reduce scope of if-else statements.

[craig.topper]

LGTM

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

setOperationAction({ISD::UADDO, ISD::USUBO, ISD::UADDSAT, ISD::USUBSAT},
                        MVT::i32, Custom);
   } else {
     setLibcallName(
         {RTLIB::SHL_I128, RTLIB::SRL_I128, RTLIB::SRA_I128, RTLIB::MUL_I128},
         nullptr);
     setLibcallName(RTLIB::MULO_I64, nullptr);
   }
 
-  if (!Subtarget.hasStdExtM() && !Subtarget.hasStdExtZmmul()) {
+  if (!Subtarget.hasStdExtM() && !Subtarget.hasStdExtZmmul())
     setOperationAction({ISD::MUL, ISD::MULHS, ISD::MULHU}, XLenVT, Expand);
-  } else {
-    if (Subtarget.is64Bit()) {
-      setOperationAction(ISD::MUL, {MVT::i32, MVT::i128}, Custom);
-    } else {
-      setOperationAction(ISD::MUL, MVT::i64, Custom);
-    }
-  }
+  else if (Subtarget.is64Bit())
+  else
 
-  if (!Subtarget.hasStdExtM()) {
+  if (!Subtarget.hasStdExtM())
     setOperationAction({ISD::SDIV, ISD::UDIV, ISD::SREM, ISD::UREM},
                        XLenVT, Expand);
-  } else {
-    if (Subtarget.is64Bit()) {
-      setOperationAction({ISD::SDIV, ISD::UDIV, ISD::UREM},
-                          {MVT::i8, MVT::i16, MVT::i32}, Custom);
-    }
-  }
+  else if (Subtarget.is64Bit())
 
   setOperationAction(
       {ISD::SDIVREM, ISD::UDIVREM, ISD::SMUL_LOHI, ISD::UMUL_LOHI}, XLenVT,
       Expand);
 
   setOperationAction({ISD::SHL_PARTS, ISD::SRL_PARTS, ISD::SRA_PARTS}, XLenVT,
                      Custom);