[RISCV] Make 'c.addi x0, imm' an alias for 'c.nop imm'.

[craig.topper]

Summary

Instead of making it an AsmParserOnly instruction, make it an alias.
This makes printing consistent with disassembly.

llvm/lib/Target/RISCV/RISCVInstrInfoC.td

 
 let rd = 0 in
 def C_NOP_HINT : RVInst16CI<0b000, 0b01, (outs), (ins simm6nonzero:$imm),
                             "c.nop", "$imm">, Sched<[WriteNop]> {
   let Inst{6-2} = imm{4-0};
   let DecoderMethod = "decodeRVCInstrSImm";
 }
 
-// Just a different syntax for the c.nop hint: c.addi x0, simm6 vs c.nop simm6.
-def C_ADDI_HINT_X0 : RVInst16CI<0b000, 0b01, (outs GPRX0:$rd_wb),
-                                (ins GPRX0:$rd, simm6nonzero:$imm),
-                                "c.addi", "$rd, $imm">,
-                     Sched<[WriteIALU, ReadIALU]> {
-  let Constraints = "$rd = $rd_wb";
-  let Inst{6-2} = imm{4-0};
-  let isAsmParserOnly = 1;
-}
-
 def C_ADDI_HINT_IMM_ZERO : RVInst16CI<0b000, 0b01, (outs GPRNoX0:$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 DecoderMethod = "decodeRVCInstrRdRs1ImmZero";

 
 } // Predicates = [HasStdExtCOrZca, HasRVCHints], hasSideEffects = 0, mayLoad = 0,
   // mayStore = 0
 
 //===----------------------------------------------------------------------===//
 // Assembler Pseudo Instructions
 //===----------------------------------------------------------------------===//
 
+let Predicates = [HasStdExtCOrZca, HasRVCHints] in {
+// Just a different syntax for the c.nop hint: c.addi x0, simm6 vs c.nop simm6.
+def : InstAlias<"c.addi x0, $imm", (C_NOP_HINT simm6nonzero:$imm), 0>;
+}
+
 let Predicates = [HasStdExtC, HasRVCHints, HasStdExtZihintntl] in {
 def : InstAlias<"c.ntl.p1", (C_ADD_HINT X0, X2)>;
 def : InstAlias<"c.ntl.pall", (C_ADD_HINT X0, X3)>;
 def : InstAlias<"c.ntl.s1", (C_ADD_HINT X0, X4)>;
 def : InstAlias<"c.ntl.all", (C_ADD_HINT X0, X5)>;
 } // Predicates = [HasStdExtC, HasRVCHints, HasStdExtZihintntl]
 
 let EmitPriority = 0 in {

llvm/test/MC/RISCV/rvc-hints-valid.s

 # RUN: llvm-mc %s -triple=riscv32 -mattr=+c -riscv-no-aliases -show-encoding \
 # RUN:     | FileCheck -check-prefixes=CHECK-ASM,CHECK-ASM-AND-OBJ %s
 # RUN: llvm-mc %s -triple riscv64 -mattr=+c -riscv-no-aliases -show-encoding \
 # RUN:     | FileCheck -check-prefixes=CHECK-ASM,CHECK-ASM-AND-OBJ %s
 # RUN: llvm-mc -filetype=obj -triple=riscv32 -mattr=+c < %s \
 # RUN:     | llvm-objdump -M no-aliases -d -r - \
-# RUN:     | FileCheck -check-prefixes=CHECK-OBJ,CHECK-ASM-AND-OBJ %s
+# RUN:     | FileCheck -check-prefixes=CHECK-ASM-AND-OBJ %s
 # RUN: llvm-mc -filetype=obj -triple=riscv64 -mattr=+c < %s \
 # RUN:     | llvm-objdump -M no-aliases -d -r - \
-# RUN:     | FileCheck -check-prefixes=CHECK-OBJ,CHECK-ASM-AND-OBJ %s
+# RUN:     | FileCheck -check-prefixes=CHECK-ASM-AND-OBJ %s
 # RUN: llvm-mc -filetype=obj -triple=riscv64 -mattr=+c < %s \
 # RUN:     | llvm-objdump -d -r - \
-# RUN:     | FileCheck -check-prefixes=CHECK-OBJ,CHECK-ASM-AND-OBJ %s
+# RUN:     | FileCheck -check-prefixes=CHECK-ASM-AND-OBJ %s
 
 # CHECK-ASM-AND-OBJ: c.nop 8
 # CHECK-ASM: encoding: [0x21,0x00]
 c.nop 8
 
-# CHECK-ASM: c.addi zero, 7
+# CHECK-ASM-AND-OBJ: c.nop 7
 # CHECK-ASM: encoding: [0x1d,0x00]
-# CHECK-OBJ: c.nop 7
 c.addi x0, 7
 
 # CHECK-ASM-AND-OBJ: c.addi a0, 0
 # CHECK-ASM: encoding: [0x01,0x05]
 c.addi a0, 0
 
 # CHECK-ASM-AND-OBJ: c.li zero, 0
 # CHECK-ASM: encoding: [0x01,0x40]