Index: llvm/test/tools/llvm-exegesis/Mips/latency-GPR64.s
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-exegesis/Mips/latency-GPR64.s
@@ -0,0 +1,11 @@
+# RUN: llvm-exegesis -mode=latency -opcode-name=AND64 | FileCheck %s
+
+CHECK:      ---
+CHECK-NEXT: mode: latency
+CHECK-NEXT: key:
+CHECK-NEXT:   instructions:
+CHECK-NEXT:     AND64
+CHECK-NEXT: config: ''
+CHECK-NEXT: register_initial_values:
+CHECK-DAG: - '[[REG1:[A-Z0-9]+_64]]=0x0'
+CHECK-LAST: ...
Index: llvm/tools/llvm-exegesis/lib/Mips/Target.cpp
===================================================================
--- llvm/tools/llvm-exegesis/lib/Mips/Target.cpp
+++ llvm/tools/llvm-exegesis/lib/Mips/Target.cpp
@@ -30,26 +30,75 @@
 };
 } // end anonymous namespace
 
-// Generates instruction to load an immediate value into a register.
-static MCInst loadImmediate(unsigned Reg, unsigned RegBitWidth,
-                            const APInt &Value) {
-  if (Value.getActiveBits() > 16)
-    llvm_unreachable("Not implemented for Values wider than 16 bits");
-  if (Value.getBitWidth() > RegBitWidth)
-    llvm_unreachable("Value must fit in the Register");
-  return MCInstBuilder(Mips::ORi)
-      .addReg(Reg)
-      .addReg(Mips::ZERO)
-      .addImm(Value.getZExtValue());
+// Generates instructions to load an immediate value into a register.
+static std::vector<MCInst> loadImmediate(unsigned Reg, bool IsGPR32,
+                                         const APInt &Value) {
+  unsigned ZeroReg;
+  unsigned ORi, LUi, SLL;
+  if (IsGPR32) {
+    ZeroReg = Mips::ZERO;
+    ORi = Mips::ORi;
+    SLL = Mips::SLL;
+    LUi = Mips::LUi;
+  } else {
+    ZeroReg = Mips::ZERO_64;
+    ORi = Mips::ORi64;
+    SLL = Mips::SLL64_64;
+    LUi = Mips::LUi64;
+  }
+
+  if (Value.isIntN(16)) {
+    return {MCInstBuilder(ORi)
+        .addReg(Reg)
+        .addReg(ZeroReg)
+        .addImm(Value.getZExtValue())};
+  }
+
+  std::vector<MCInst> Instructions;
+  if (Value.isIntN(32)) {
+    const uint16_t HiBits = Value.getHiBits(16).getZExtValue();
+    if (!IsGPR32 && Value.getActiveBits() == 32) {
+      // Expand to an ORi instead of a LUi to avoid sign-extending into the
+      // upper 32 bits.
+      Instructions.push_back(
+          MCInstBuilder(ORi)
+              .addReg(Reg)
+              .addReg(ZeroReg)
+              .addImm(HiBits));
+      Instructions.push_back(
+          MCInstBuilder(SLL)
+              .addReg(Reg)
+              .addReg(Reg)
+              .addImm(16));
+    } else {
+      Instructions.push_back(
+          MCInstBuilder(LUi)
+              .addReg(Reg)
+              .addImm(HiBits));
+    }
+
+    const uint16_t LoBits = Value.getLoBits(16).getZExtValue();
+    if (LoBits) {
+      Instructions.push_back(
+          MCInstBuilder(ORi)
+          .addReg(Reg)
+          .addReg(ZeroReg)
+          .addImm(LoBits));
+    }
+
+    return std::move(Instructions);
+  }
+
+  llvm_unreachable("Not implemented for values wider than 32 bits");
 }
 
 std::vector<MCInst> ExegesisMipsTarget::setRegTo(const MCSubtargetInfo &STI,
                                                  unsigned Reg,
                                                  const APInt &Value) const {
   if (Mips::GPR32RegClass.contains(Reg))
-    return {loadImmediate(Reg, 32, Value)};
+    return loadImmediate(Reg, true, Value);
   if (Mips::GPR64RegClass.contains(Reg))
-    return {loadImmediate(Reg, 64, Value)};
+    return loadImmediate(Reg, false, Value);
   errs() << "setRegTo is not implemented, results will be unreliable\n";
   return {};
 }
Index: llvm/unittests/tools/llvm-exegesis/Mips/TargetTest.cpp
===================================================================
--- llvm/unittests/tools/llvm-exegesis/Mips/TargetTest.cpp
+++ llvm/unittests/tools/llvm-exegesis/Mips/TargetTest.cpp
@@ -44,9 +44,22 @@
   return Property(&MCInst::getOpcode, Eq(Opcode));
 }
 
-Matcher<MCInst> IsLoadLowImm(int64_t Reg, int64_t Value) {
-  return AllOf(OpcodeIs(Mips::ORi),
-               ElementsAre(IsReg(Reg), IsReg(Mips::ZERO), IsImm(Value)));
+Matcher<MCInst> IsLoadLow16BitImm(unsigned Reg, int64_t Value, bool IsGPR32) {
+  const unsigned ZeroReg = IsGPR32 ? Mips::ZERO : Mips::ZERO_64;
+  const unsigned ORi = IsGPR32 ? Mips::ORi : Mips::ORi64;
+  return AllOf(OpcodeIs(ORi),
+               ElementsAre(IsReg(Reg), IsReg(ZeroReg), IsImm(Value)));
+}
+
+Matcher<MCInst> IsLoadHigh16BitImm(unsigned Reg, int64_t Value, bool IsGPR32) {
+  const unsigned LUi = IsGPR32 ? Mips::LUi : Mips::LUi64;
+  return AllOf(OpcodeIs(LUi), ElementsAre(IsReg(Reg), IsImm(Value)));
+}
+
+Matcher<MCInst> IsShift(unsigned Reg, uint16_t Amount, bool IsGPR32) {
+  const unsigned SLL = IsGPR32 ? Mips::SLL : Mips::SLL64_64;
+  return AllOf(OpcodeIs(SLL),
+               ElementsAre(IsReg(Reg), IsReg(Reg), IsImm(Amount)));
 }
 
 constexpr const char kTriple[] = "mips-unknown-linux";
@@ -70,11 +83,53 @@
   LLVMState State;
 };
 
-TEST_F(MipsTargetTest, SetRegToConstant) {
+TEST_F(MipsTargetTest, SetGPR32RegTo16BitValue) {
   const uint16_t Value = 0xFFFFU;
   const unsigned Reg = Mips::T0;
   EXPECT_THAT(setRegTo(Reg, APInt(16, Value)),
-              ElementsAre(IsLoadLowImm(Reg, Value)));
+              ElementsAre(IsLoadLow16BitImm(Reg, Value, true)));
+}
+
+TEST_F(MipsTargetTest, SetGPR64RegTo16BitValue) {
+  const uint16_t Value = 0xFFFFU;
+  const unsigned Reg = Mips::T0_64;
+  EXPECT_THAT(setRegTo(Reg, APInt(16, Value)),
+              ElementsAre(IsLoadLow16BitImm(Reg, Value, false)));
+}
+
+TEST_F(MipsTargetTest, SetGPR32RegTo32BitValue) {
+  const uint32_t Value0 = 0xFFFF0000UL;
+  const unsigned Reg0 = Mips::T0;
+  EXPECT_THAT(setRegTo(Reg0, APInt(32, Value0)),
+              ElementsAre(IsLoadHigh16BitImm(Reg0, 0xFFFFU, true)));
+  const uint32_t Value1 = 0xFFFFFFFFUL;
+  const unsigned Reg1 = Mips::T1;
+  EXPECT_THAT(setRegTo(Reg1, APInt(32, Value1)),
+              ElementsAre(IsLoadHigh16BitImm(Reg1, 0xFFFFU, true),
+                          IsLoadLow16BitImm(Reg1, 0xFFFFU, true)));
+}
+
+TEST_F(MipsTargetTest, SetGPR64RegTo32BitValue) {
+  const uint32_t Value0 = 0x7FFF0000UL;
+  const unsigned Reg0 = Mips::T0_64;
+  EXPECT_THAT(setRegTo(Reg0, APInt(32, Value0)),
+              ElementsAre(IsLoadHigh16BitImm(Reg0, 0x7FFFU, false)));
+  const uint32_t Value1 = 0x7FFFFFFFUL;
+  const unsigned Reg1 = Mips::T1_64;
+  EXPECT_THAT(setRegTo(Reg1, APInt(32, Value1)),
+              ElementsAre(IsLoadHigh16BitImm(Reg1, 0x7FFFU, false),
+                          IsLoadLow16BitImm(Reg1, 0xFFFFU, false)));
+  const uint32_t Value2 = 0xFFFF0000UL;
+  const unsigned Reg2 = Mips::T2_64;
+  EXPECT_THAT(setRegTo(Reg2, APInt(32, Value2)),
+              ElementsAre(IsLoadLow16BitImm(Reg2, 0xFFFFU, false),
+                          IsShift(Reg2, 16, false)));
+  const uint32_t Value3 = 0xFFFFFFFFUL;
+  const unsigned Reg3 = Mips::T3_64;
+  EXPECT_THAT(setRegTo(Reg3, APInt(32, Value3)),
+              ElementsAre(IsLoadLow16BitImm(Reg3, 0xFFFFU, false),
+                          IsShift(Reg3, 16, false),
+                          IsLoadLow16BitImm(Reg3, 0xFFFFU, false)));
 }
 
 TEST_F(MipsTargetTest, DefaultPfmCounters) {