[RISCV] Set isAsCheapAsAMove for ADDI, ORI, XORI, LUI

Summary:
Affected instructions:
PseudoLI simplest form (ADDI with X0)
ALU operations with immediate (they do not set status flag - ADDI, ORI, XORI)

Reviewers: asb

Reviewed By: asb

Subscribers: shiva0217, rkruppe, kito-cheng, asb, rbar, johnrusso, simoncook, sabuasal, niosHD, zzheng, edward-jones, mgrang, rogfer01, MartinMosbeck, brucehoult, the_o, PkmX, jocewei

Differential Revision: https://reviews.llvm.org/D56526

llvm-svn: 352010

llvm/lib/Target/RISCV/RISCVInstrInfo.cpp

@@ -447,3 +447,16 @@ unsigned RISCVInstrInfo::getInstSizeInBytes(const MachineInstr &MI) const {
   }
   }
 }
+
+bool RISCVInstrInfo::isAsCheapAsAMove(const MachineInstr &MI) const {
+  const unsigned Opcode = MI.getOpcode();
+  switch(Opcode) {
+    default:
+      break;
+    case RISCV::ADDI:
+    case RISCV::ORI:
+    case RISCV::XORI:
+      return (MI.getOperand(1).isReg() && MI.getOperand(1).getReg() == RISCV::X0);
+  }
+  return MI.isAsCheapAsAMove();
+}

llvm/lib/Target/RISCV/RISCVInstrInfo.h

@@ -78,6 +78,8 @@ public:
 
   bool isBranchOffsetInRange(unsigned BranchOpc,
                              int64_t BrOffset) const override;
+
+  bool isAsCheapAsAMove(const MachineInstr &MI) const override;
 };
 }
 #endif

llvm/lib/Target/RISCV/RISCVInstrInfo.td

@@ -312,7 +312,7 @@ class Priv<string opcodestr, bits<7> funct7>
 //===----------------------------------------------------------------------===//
 
 let hasSideEffects = 0, mayLoad = 0, mayStore = 0 in {
-let isReMaterializable = 1 in
+let isReMaterializable = 1, isAsCheapAsAMove = 1 in
 def LUI : RVInstU<OPC_LUI, (outs GPR:$rd), (ins uimm20_lui:$imm20),
                   "lui", "$rd, $imm20">;
 
@@ -348,13 +348,13 @@ def SW : Store_rri<0b010, "sw">;
 
 // ADDI isn't always rematerializable, but isReMaterializable will be used as
 // a hint which is verified in isReallyTriviallyReMaterializable.
-let isReMaterializable = 1 in
+let isReMaterializable = 1, isAsCheapAsAMove = 1 in
 def ADDI  : ALU_ri<0b000, "addi">;
 
 def SLTI  : ALU_ri<0b010, "slti">;
 def SLTIU : ALU_ri<0b011, "sltiu">;
 
-let isReMaterializable = 1 in {
+let isReMaterializable = 1, isAsCheapAsAMove = 1 in {
 def XORI  : ALU_ri<0b100, "xori">;
 def ORI   : ALU_ri<0b110, "ori">;
 }