[RISCV] Add a default common assignment of Inst{6-2} to the RVInst16CI base class.

Many instructions assign all or a subset of Inst{6-2} to Imm{4-0}.
Make this the default. Subsets of Inst{6-2} can be overridden as
needed by derived classes/records which we already do with Inst{12}
in a few places.

Author: topperc

llvm/lib/Target/RISCV/RISCVInstrFormatsC.td

@@ -36,7 +36,8 @@ class RVInst16CR<bits<4> funct4, bits<2> opcode, dag outs, dag ins,
 
 // The immediate value encoding differs for each instruction, so each subclass
 // is responsible for setting the appropriate bits in the Inst field.
-// The bits Inst{6-2} must be set for each instruction.
+// The bits Inst{12} and Inst{6-2} may need to be set differently for some
+// instructions.
 class RVInst16CI<bits<3> funct3, bits<2> opcode, dag outs, dag ins,
                  string opcodestr, string argstr>
     : RVInst16<outs, ins, opcodestr, argstr, [], InstFormatCI> {
@@ -46,6 +47,7 @@ class RVInst16CI<bits<3> funct3, bits<2> opcode, dag outs, dag ins,
   let Inst{15-13} = funct3;
   let Inst{12} = imm{5};
   let Inst{11-7} = rd;
+  let Inst{6-2} = imm{4-0};
   let Inst{1-0} = opcode;
 }
 

llvm/lib/Target/RISCV/RISCVInstrInfoC.td

@@ -402,7 +402,6 @@ def C_NOP : RVInst16CI<0b000, 0b01, (outs), (ins), "c.nop", "">,
             Sched<[WriteNop]> {
   let rd = 0;
   let imm = 0;
-  let Inst{6-2} = 0;
 }
 
 let hasSideEffects = 0, mayLoad = 0, mayStore = 0 in
@@ -411,7 +410,6 @@ def C_ADDI : RVInst16CI<0b000, 0b01, (outs GPRNoX0:$rd_wb),
                         "c.addi", "$rd, $imm">,
              Sched<[WriteIALU, ReadIALU]> {
   let Constraints = "$rd = $rd_wb";
-  let Inst{6-2} = imm{4-0};
 }
 
 // Alternate syntax for c.nop. Converted to C_NOP by the assembler.
@@ -433,15 +431,12 @@ def C_ADDIW : RVInst16CI<0b001, 0b01, (outs GPRNoX0:$rd_wb),
                          "c.addiw", "$rd, $imm">,
               Sched<[WriteIALU32, ReadIALU32]> {
   let Constraints = "$rd = $rd_wb";
-  let Inst{6-2} = imm{4-0};
 }
 
 let hasSideEffects = 0, mayLoad = 0, mayStore = 0 in
 def C_LI : RVInst16CI<0b010, 0b01, (outs GPRNoX0:$rd), (ins simm6:$imm),
                       "c.li", "$rd, $imm">,
-           Sched<[WriteIALU]> {
-  let Inst{6-2} = imm{4-0};
-}
+           Sched<[WriteIALU]>;
 
 let hasSideEffects = 0, mayLoad = 0, mayStore = 0 in
 def C_ADDI16SP : RVInst16CI<0b011, 0b01, (outs SP:$rd_wb),
@@ -461,9 +456,7 @@ let hasSideEffects = 0, mayLoad = 0, mayStore = 0 in
 def C_LUI : RVInst16CI<0b011, 0b01, (outs GPRNoX0X2:$rd),
                        (ins c_lui_imm:$imm),
                        "c.lui", "$rd, $imm">,
-            Sched<[WriteIALU]> {
-  let Inst{6-2} = imm{4-0};
-}
+            Sched<[WriteIALU]>;
 
 def C_SRLI : Shift_right<0b00, "c.srli", GPRC, uimmlog2xlennonzero>,
              Sched<[WriteShiftImm, ReadShiftImm]>;
@@ -513,41 +506,35 @@ def C_SLLI : RVInst16CI<0b000, 0b10, (outs GPRNoX0:$rd_wb),
                         "c.slli", "$rd, $imm">,
              Sched<[WriteShiftImm, ReadShiftImm]> {
   let Constraints = "$rd = $rd_wb";
-  let Inst{6-2} = imm{4-0};
 }
 
 let Predicates = [HasStdExtCOrZcd, HasStdExtD] in
 def C_FLDSP  : CStackLoad<0b001, "c.fldsp", FPR64, uimm9_lsb000>,
                Sched<[WriteFLD64, ReadFMemBase]> {
-  let Inst{6-5} = imm{4-3};
   let Inst{4-2} = imm{8-6};
 }
 
 def C_LWSP : CStackLoad<0b010, "c.lwsp", GPRNoX0, uimm8_lsb00>,
              Sched<[WriteLDW, ReadMemBase]> {
-  let Inst{6-4} = imm{4-2};
   let Inst{3-2} = imm{7-6};
 }
 
 let isCodeGenOnly = 1 in
 def C_LWSP_INX : CStackLoad<0b010, "c.lwsp", GPRF32NoX0, uimm8_lsb00>,
                  Sched<[WriteLDW, ReadMemBase]> {
-  let Inst{6-4} = imm{4-2};
   let Inst{3-2} = imm{7-6};
 }
 
 let DecoderNamespace = "RISCV32Only_",
     Predicates = [HasStdExtCOrZcfOrZce, HasStdExtF, IsRV32] in
 def C_FLWSP  : CStackLoad<0b011, "c.flwsp", FPR32, uimm8_lsb00>,
                Sched<[WriteFLD32, ReadFMemBase]> {
-  let Inst{6-4} = imm{4-2};
   let Inst{3-2} = imm{7-6};
 }
 
 let Predicates = [HasStdExtCOrZca, IsRV64] in
 def C_LDSP : CStackLoad<0b011, "c.ldsp", GPRNoX0, uimm9_lsb000>,
              Sched<[WriteLDD, ReadMemBase]> {
-  let Inst{6-5} = imm{4-3};
   let Inst{4-2} = imm{8-6};
 }
 
@@ -636,23 +623,20 @@ let Predicates = [HasStdExtCOrZca, HasRVCHints], hasSideEffects = 0, mayLoad = 0
 def C_NOP_HINT : RVInst16CI<0b000, 0b01, (outs), (ins simm6nonzero:$imm),
                             "c.nop", "$imm">, Sched<[WriteNop]> {
   let rd = 0;
-  let Inst{6-2} = imm{4-0};
 }
 
 def C_ADDI_HINT_IMM_ZERO : RVInst16CI<0b000, 0b01, (outs GPRNoX0:$rd_wb),
                                       (ins GPRNoX0:$rd, immzero:$imm),
                                       "c.addi", "$rd, $imm">,
                            Sched<[WriteIALU, ReadIALU]> {
   let Constraints = "$rd = $rd_wb";
-  let Inst{12} = 0;
-  let Inst{6-2} = 0;
+  let imm = 0;
   let DecoderMethod = "decodeRVCInstrRdRs1ImmZero";
 }
 
 def C_LI_HINT : RVInst16CI<0b010, 0b01, (outs GPRX0:$rd), (ins simm6:$imm),
                            "c.li", "$rd, $imm">,
                 Sched<[WriteIALU]> {
-  let Inst{6-2} = imm{4-0};
   let Inst{11-7} = 0;
   let DecoderMethod = "decodeRVCInstrRdSImm";
 }
@@ -661,7 +645,6 @@ def C_LUI_HINT : RVInst16CI<0b011, 0b01, (outs GPRX0:$rd),
                             (ins c_lui_imm:$imm),
                             "c.lui", "$rd, $imm">,
                  Sched<[WriteIALU]> {
-  let Inst{6-2} = imm{4-0};
   let Inst{11-7} = 0;
   let DecoderMethod = "decodeRVCInstrRdSImm";
 }
@@ -686,7 +669,6 @@ def C_SLLI_HINT : RVInst16CI<0b000, 0b10, (outs GPRX0:$rd_wb),
                              "c.slli", "$rd, $imm">,
                   Sched<[WriteShiftImm, ReadShiftImm]> {
   let Constraints = "$rd = $rd_wb";
-  let Inst{6-2} = imm{4-0};
   let Inst{11-7} = 0;
   let DecoderMethod = "decodeRVCInstrRdRs1UImm";
 }
@@ -695,8 +677,7 @@ def C_SLLI64_HINT : RVInst16CI<0b000, 0b10, (outs GPR:$rd_wb), (ins GPR:$rd),
                                "c.slli64", "$rd">,
                     Sched<[WriteShiftImm, ReadShiftImm]> {
   let Constraints = "$rd = $rd_wb";
-  let Inst{6-2} = 0;
-  let Inst{12} = 0;
+  let imm = 0;
 }
 
 def C_SRLI64_HINT : RVInst16CB<0b100, 0b01, (outs GPRC:$rd),