3 files changed, 89 insertions, 0 deletions

diff --git a/llvm/lib/Target/Mips/MipsInstructionSelector.cpp b/llvm/lib/Target/Mips/MipsInstructionSelector.cpp
index 6c5b83021f7..fbc15649c8a 100644
--- a/llvm/lib/Target/Mips/MipsInstructionSelector.cpp
+++ b/llvm/lib/Target/Mips/MipsInstructionSelector.cpp
@@ -15,6 +15,7 @@
 #include "MipsRegisterBankInfo.h"
 #include "MipsTargetMachine.h"
 #include "llvm/CodeGen/GlobalISel/InstructionSelectorImpl.h"
+#include "llvm/CodeGen/GlobalISel/MachineIRBuilder.h"
 
 #define DEBUG_TYPE "mips-isel"
 
@@ -193,7 +194,85 @@ bool MipsInstructionSelector::select(MachineInstr &I,
     I.eraseFromParent();
     return true;
   }
+  case G_ICMP: {
+    struct Instr {
+      unsigned Opcode, Def, LHS, RHS;
+      Instr(unsigned Opcode, unsigned Def, unsigned LHS, unsigned RHS)
+          : Opcode(Opcode), Def(Def), LHS(LHS), RHS(RHS){};
+
+      bool hasImm() const {
+        if (Opcode == Mips::SLTiu || Opcode == Mips::XORi)
+          return true;
+        return false;
+      }
+    };
+
+    SmallVector<struct Instr, 2> Instructions;
+    unsigned ICMPReg = I.getOperand(0).getReg();
+    unsigned Temp = MRI.createVirtualRegister(&Mips::GPR32RegClass);
+    unsigned LHS = I.getOperand(2).getReg();
+    unsigned RHS = I.getOperand(3).getReg();
+    CmpInst::Predicate Cond =
+        static_cast<CmpInst::Predicate>(I.getOperand(1).getPredicate());
+
+    switch (Cond) {
+    case CmpInst::ICMP_EQ: // LHS == RHS -> (LHS ^ RHS) < 1
+      Instructions.emplace_back(Mips::XOR, Temp, LHS, RHS);
+      Instructions.emplace_back(Mips::SLTiu, ICMPReg, Temp, 1);
+      break;
+    case CmpInst::ICMP_NE: // LHS != RHS -> 0 < (LHS ^ RHS)
+      Instructions.emplace_back(Mips::XOR, Temp, LHS, RHS);
+      Instructions.emplace_back(Mips::SLTu, ICMPReg, Mips::ZERO, Temp);
+      break;
+    case CmpInst::ICMP_UGT: // LHS >  RHS -> RHS < LHS
+      Instructions.emplace_back(Mips::SLTu, ICMPReg, RHS, LHS);
+      break;
+    case CmpInst::ICMP_UGE: // LHS >= RHS -> !(LHS < RHS)
+      Instructions.emplace_back(Mips::SLTu, Temp, LHS, RHS);
+      Instructions.emplace_back(Mips::XORi, ICMPReg, Temp, 1);
+      break;
+    case CmpInst::ICMP_ULT: // LHS <  RHS -> LHS < RHS
+      Instructions.emplace_back(Mips::SLTu, ICMPReg, LHS, RHS);
+      break;
+    case CmpInst::ICMP_ULE: // LHS <= RHS -> !(RHS < LHS)
+      Instructions.emplace_back(Mips::SLTu, Temp, RHS, LHS);
+      Instructions.emplace_back(Mips::XORi, ICMPReg, Temp, 1);
+      break;
+    case CmpInst::ICMP_SGT: // LHS >  RHS -> RHS < LHS
+      Instructions.emplace_back(Mips::SLT, ICMPReg, RHS, LHS);
+      break;
+    case CmpInst::ICMP_SGE: // LHS >= RHS -> !(LHS < RHS)
+      Instructions.emplace_back(Mips::SLT, Temp, LHS, RHS);
+      Instructions.emplace_back(Mips::XORi, ICMPReg, Temp, 1);
+      break;
+    case CmpInst::ICMP_SLT: // LHS <  RHS -> LHS < RHS
+      Instructions.emplace_back(Mips::SLT, ICMPReg, LHS, RHS);
+      break;
+    case CmpInst::ICMP_SLE: // LHS <= RHS -> !(RHS < LHS)
+      Instructions.emplace_back(Mips::SLT, Temp, RHS, LHS);
+      Instructions.emplace_back(Mips::XORi, ICMPReg, Temp, 1);
+      break;
+    default:
+      return false;
+    }
+
+    MachineIRBuilder B(I);
+    for (const struct Instr &Instruction : Instructions) {
+      MachineInstrBuilder MIB =
+          B.buildInstr(Instruction.Opcode, Instruction.Def, Instruction.LHS);
+
+      if (Instruction.hasImm())
+        MIB.addImm(Instruction.RHS);
+      else
+        MIB.addUse(Instruction.RHS);
+
+      if (!MIB.constrainAllUses(TII, TRI, RBI))
+        return false;
+    }
 
+    I.eraseFromParent();
+    return true;
+  }
   default:
     return false;
   }
diff --git a/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp b/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp
index 7e7094061ec..4da1fb205e5 100644
--- a/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsLegalizerInfo.cpp
@@ -32,6 +32,10 @@ MipsLegalizerInfo::MipsLegalizerInfo(const MipsSubtarget &ST) {
   getActionDefinitionsBuilder({G_AND, G_OR, G_XOR, G_SHL, G_ASHR, G_LSHR})
       .legalFor({s32});
 
+  getActionDefinitionsBuilder(G_ICMP)
+      .legalFor({{s32, s32}})
+      .minScalar(0, s32);
+
   getActionDefinitionsBuilder(G_CONSTANT)
       .legalFor({s32});
 
diff --git a/llvm/lib/Target/Mips/MipsRegisterBankInfo.cpp b/llvm/lib/Target/Mips/MipsRegisterBankInfo.cpp
index c7844c30b32..96ca1cdd643 100644
--- a/llvm/lib/Target/Mips/MipsRegisterBankInfo.cpp
+++ b/llvm/lib/Target/Mips/MipsRegisterBankInfo.cpp
@@ -98,6 +98,12 @@ MipsRegisterBankInfo::getInstrMapping(const MachineInstr &MI) const {
     OperandsMapping =
         getOperandsMapping({&Mips::ValueMappings[Mips::GPRIdx], nullptr});
     break;
+  case G_ICMP:
+    OperandsMapping =
+        getOperandsMapping({&Mips::ValueMappings[Mips::GPRIdx], nullptr,
+                            &Mips::ValueMappings[Mips::GPRIdx],
+                            &Mips::ValueMappings[Mips::GPRIdx]});
+    break;
   default:
     return getInvalidInstructionMapping();
   }