diff --git a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp
--- a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp
+++ b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.cpp
@@ -176,7 +176,10 @@
 }
 
 unsigned LoongArchInstrInfo::getInstSizeInBytes(const MachineInstr &MI) const {
-  if (MI.getOpcode() == TargetOpcode::INLINEASM) {
+  unsigned Opcode = MI.getOpcode();
+
+  if (Opcode == TargetOpcode::INLINEASM ||
+      Opcode == TargetOpcode::INLINEASM_BR) {
     const MachineFunction *MF = MI.getParent()->getParent();
     const MCAsmInfo *MAI = MF->getTarget().getMCAsmInfo();
     return getInlineAsmLength(MI.getOperand(0).getSymbolName(), *MAI);
diff --git a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td
--- a/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td
+++ b/llvm/lib/Target/LoongArch/LoongArchInstrInfo.td
@@ -1159,6 +1159,7 @@
   let mayLoad = 1;
   let mayStore = 1;
   let hasSideEffects = 0;
+  let Size = 36;
 }
 
 def PseudoMaskedAtomicSwap32 : PseudoMaskedAM;
@@ -1172,6 +1173,7 @@
   let mayLoad = 1;
   let mayStore = 1;
   let hasSideEffects = 0;
+  let Size = 24;
 }
 
 def PseudoAtomicSwap32 : PseudoAM;
@@ -1192,6 +1194,7 @@
   let mayLoad = 1;
   let mayStore = 1;
   let hasSideEffects = 0;
+  let Size = 48;
 }
 
 def PseudoMaskedAtomicLoadUMax32 : PseudoMaskedAMUMinUMax;
@@ -1206,6 +1209,7 @@
   let mayLoad = 1;
   let mayStore = 1;
   let hasSideEffects = 0;
+  let Size = 36;
 }
 
 def PseudoCmpXchg32 : PseudoCmpXchg;
@@ -1219,6 +1223,7 @@
   let mayLoad = 1;
   let mayStore = 1;
   let hasSideEffects = 0;
+  let Size = 44;
 }
 
 class AtomicPat<Intrinsic intrin, Pseudo AMInst>
diff --git a/llvm/unittests/Target/LoongArch/CMakeLists.txt b/llvm/unittests/Target/LoongArch/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/llvm/unittests/Target/LoongArch/CMakeLists.txt
@@ -0,0 +1,25 @@
+include_directories(
+  ${LLVM_MAIN_SRC_DIR}/lib/Target/LoongArch
+  ${LLVM_BINARY_DIR}/lib/Target/LoongArch
+  )
+
+set(LLVM_LINK_COMPONENTS
+  AsmParser
+  CodeGen
+  Core
+  GlobalISel
+  LoongArchCodeGen
+  LoongArchDesc
+  LoongArchInfo
+  MC
+  MIRParser
+  SelectionDAG
+  Support
+  Target
+  )
+
+add_llvm_target_unittest(LoongArchTests
+  InstSizes.cpp
+  )
+
+set_property(TARGET LoongArchTests PROPERTY FOLDER "Tests/UnitTests/TargetTests")
diff --git a/llvm/unittests/Target/LoongArch/InstSizes.cpp b/llvm/unittests/Target/LoongArch/InstSizes.cpp
new file mode 100644
--- /dev/null
+++ b/llvm/unittests/Target/LoongArch/InstSizes.cpp
@@ -0,0 +1,137 @@
+#include "LoongArchSubtarget.h"
+#include "LoongArchTargetMachine.h"
+#include "llvm/CodeGen/MIRParser/MIRParser.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
+#include "llvm/MC/TargetRegistry.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/TargetSelect.h"
+
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+std::unique_ptr<LLVMTargetMachine> createTargetMachine() {
+  auto TT(Triple::normalize("loongarch64--"));
+  std::string CPU("generic-la64");
+  std::string FS("+64bit");
+
+  LLVMInitializeLoongArchTargetInfo();
+  LLVMInitializeLoongArchTarget();
+  LLVMInitializeLoongArchTargetMC();
+
+  std::string Error;
+  const Target *TheTarget = TargetRegistry::lookupTarget(TT, Error);
+
+  return std::unique_ptr<LLVMTargetMachine>(
+      static_cast<LLVMTargetMachine *>(TheTarget->createTargetMachine(
+          TT, CPU, FS, TargetOptions(), None, None, CodeGenOpt::Default)));
+}
+
+std::unique_ptr<LoongArchInstrInfo> createInstrInfo(TargetMachine *TM) {
+  LoongArchSubtarget ST(TM->getTargetTriple(), std::string(TM->getTargetCPU()),
+                        std::string(TM->getTargetCPU()),
+                        std::string(TM->getTargetFeatureString()), "lp64d",
+                        *TM);
+  return std::make_unique<LoongArchInstrInfo>(ST);
+}
+
+/// The \p InputIRSnippet is only needed for things that can't be expressed in
+/// the \p InputMIRSnippet (global variables etc)
+/// Inspired by AArch64
+void runChecks(
+    LLVMTargetMachine *TM, LoongArchInstrInfo *II,
+    const StringRef InputIRSnippet, const StringRef InputMIRSnippet,
+    std::function<void(LoongArchInstrInfo &, MachineFunction &)> Checks) {
+  LLVMContext Context;
+
+  auto MIRString = "--- |\n"
+                   "  declare void @sizes()\n" +
+                   InputIRSnippet.str() +
+                   "...\n"
+                   "---\n"
+                   "name: sizes\n"
+                   "jumpTable:\n"
+                   "  kind:            block-address\n"
+                   "  entries:\n"
+                   "    - id:              0\n"
+                   "      blocks:          [ '%bb.0' ]\n"
+                   "body: |\n"
+                   "  bb.0:\n" +
+                   InputMIRSnippet.str();
+
+  std::unique_ptr<MemoryBuffer> MBuffer = MemoryBuffer::getMemBuffer(MIRString);
+  std::unique_ptr<MIRParser> MParser =
+      createMIRParser(std::move(MBuffer), Context);
+  ASSERT_TRUE(MParser);
+
+  std::unique_ptr<Module> M = MParser->parseIRModule();
+  ASSERT_TRUE(M);
+
+  M->setTargetTriple(TM->getTargetTriple().getTriple());
+  M->setDataLayout(TM->createDataLayout());
+
+  MachineModuleInfo MMI(TM);
+  bool Res = MParser->parseMachineFunctions(*M, MMI);
+  ASSERT_FALSE(Res);
+
+  auto F = M->getFunction("sizes");
+  ASSERT_TRUE(F != nullptr);
+  auto &MF = MMI.getOrCreateMachineFunction(*F);
+
+  Checks(*II, MF);
+}
+
+} // anonymous namespace
+
+TEST(InstSizes, INLINEASM_BR) {
+  std::unique_ptr<LLVMTargetMachine> TM = createTargetMachine();
+  std::unique_ptr<LoongArchInstrInfo> II = createInstrInfo(TM.get());
+
+  runChecks(TM.get(), II.get(), "",
+            // clang-format off
+            "  INLINEASM_BR &nop, 1 /* sideeffect attdialect */, 13 /* imm */, %jump-table.0\n",
+            // clang-format on
+            [](LoongArchInstrInfo &II, MachineFunction &MF) {
+              auto I = MF.begin()->begin();
+              EXPECT_EQ(4u, II.getInstSizeInBytes(*I));
+            });
+}
+
+TEST(InstSizes, SPACE) {
+  std::unique_ptr<LLVMTargetMachine> TM = createTargetMachine();
+  std::unique_ptr<LoongArchInstrInfo> II = createInstrInfo(TM.get());
+
+  runChecks(TM.get(), II.get(), "", "  INLINEASM &\".space 1024\", 1\n",
+            [](LoongArchInstrInfo &II, MachineFunction &MF) {
+              auto I = MF.begin()->begin();
+              EXPECT_EQ(1024u, II.getInstSizeInBytes(*I));
+            });
+}
+
+TEST(InstSizes, AtomicPseudo) {
+  std::unique_ptr<LLVMTargetMachine> TM = createTargetMachine();
+  std::unique_ptr<LoongArchInstrInfo> II = createInstrInfo(TM.get());
+
+  runChecks(
+      TM.get(), II.get(), "",
+      // clang-format off
+      "    dead early-clobber renamable $r10, dead early-clobber renamable $r11 = PseudoMaskedAtomicLoadAdd32 renamable $r7, renamable $r6, renamable $r8, 4\n"
+      "    dead early-clobber renamable $r10, dead early-clobber renamable $r11 = PseudoAtomicLoadAdd32 renamable $r7, renamable $r6\n"
+      "    dead early-clobber renamable $r5, dead early-clobber renamable $r9, dead early-clobber renamable $r10 = PseudoMaskedAtomicLoadUMax32 renamable $r7, renamable $r6, renamable $r8, 4\n"
+      "    dead early-clobber renamable $r5, dead early-clobber renamable $r9 = PseudoCmpXchg32 renamable $r7, renamable $r4, renamable $r6\n"
+      "    dead early-clobber renamable $r5, dead early-clobber renamable $r9 = PseudoMaskedCmpXchg32 killed renamable $r7, killed renamable $r4, killed renamable $r6, killed renamable $r8, 4\n",
+      // clang-format on
+      [](LoongArchInstrInfo &II, MachineFunction &MF) {
+        auto I = MF.begin()->begin();
+        EXPECT_EQ(36u, II.getInstSizeInBytes(*I));
+        ++I;
+        EXPECT_EQ(24u, II.getInstSizeInBytes(*I));
+        ++I;
+        EXPECT_EQ(48u, II.getInstSizeInBytes(*I));
+        ++I;
+        EXPECT_EQ(36u, II.getInstSizeInBytes(*I));
+        ++I;
+        EXPECT_EQ(44u, II.getInstSizeInBytes(*I));
+      });
+}