diff --git a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
index 9049a016b2b9b..735b2b0a1627d 100644
--- a/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenBuiltin.cpp
@@ -21,6 +21,7 @@
 #include "mlir/Support/LLVM.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/GlobalDecl.h"
+#include "clang/Basic/Builtins.h"
 #include "clang/CIR/MissingFeatures.h"
 #include "llvm/Support/ErrorHandling.h"
 
@@ -269,6 +270,22 @@ RValue CIRGenFunction::emitBuiltinExpr(const GlobalDecl &gd, unsigned builtinID,
   case Builtin::BI__builtin_rotateright32:
   case Builtin::BI__builtin_rotateright64:
     return emitRotate(e, /*isRotateLeft=*/false);
+
+  case Builtin::BI__builtin_trap: {
+    builder.create<cir::TrapOp>(loc);
+    // Note that cir.trap is a terminator so we need to start a new dummy block
+    // to preserve the builder's insertion point.
+    builder.createBlock(builder.getBlock()->getParent());
+    return RValue::get(nullptr);
+  }
+
+  case Builtin::BI__builtin_unreachable: {
+    emitUnreachable(e->getExprLoc());
+    // Note that cir.unreachable is a terminator so we need to start a new dummy
+    // block to preserve the builder's insertion point.
+    builder.createBlock(builder.getBlock()->getParent());
+    return RValue::get(nullptr);
+  }
   }
 
   // If this is an alias for a lib function (e.g. __builtin_sin), emit
diff --git a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
index c18498f80e99f..ae8da71219bf3 100644
--- a/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
+++ b/clang/lib/CIR/CodeGen/CIRGenExpr.cpp
@@ -1780,6 +1780,11 @@ LValue CIRGenFunction::emitLoadOfReferenceLValue(Address refAddr,
                         pointeeBaseInfo);
 }
 
+void CIRGenFunction::emitUnreachable(clang::SourceLocation loc) {
+  assert(!cir::MissingFeatures::sanitizers());
+  builder.create<cir::UnreachableOp>(getLoc(loc));
+}
+
 mlir::Value CIRGenFunction::createDummyValue(mlir::Location loc,
                                              clang::QualType qt) {
   mlir::Type t = convertType(qt);
diff --git a/clang/lib/CIR/CodeGen/CIRGenFunction.h b/clang/lib/CIR/CodeGen/CIRGenFunction.h
index 603f75078c519..01049424f90cb 100644
--- a/clang/lib/CIR/CodeGen/CIRGenFunction.h
+++ b/clang/lib/CIR/CodeGen/CIRGenFunction.h
@@ -1201,6 +1201,10 @@ class CIRGenFunction : public CIRGenTypeCache {
 
   LValue emitUnaryOpLValue(const clang::UnaryOperator *e);
 
+  /// Emit a reached-unreachable diagnostic if \p loc is valid and runtime
+  /// checking is enabled. Otherwise, just emit an unreachable instruction.
+  void emitUnreachable(clang::SourceLocation loc);
+
   /// This method handles emission of any variable declaration
   /// inside a function, including static vars etc.
   void emitVarDecl(const clang::VarDecl &d);
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
index 957a51ab334aa..ce245681e4443 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.cpp
@@ -2214,7 +2214,8 @@ void ConvertCIRToLLVMPass::runOnOperation() {
                CIRToLLVMVecShuffleDynamicOpLowering,
                CIRToLLVMVecShuffleOpLowering,
                CIRToLLVMVecSplatOpLowering,
-               CIRToLLVMVecTernaryOpLowering
+               CIRToLLVMVecTernaryOpLowering,
+               CIRToLLVMUnreachableOpLowering
       // clang-format on
       >(converter, patterns.getContext());
 
@@ -2270,6 +2271,13 @@ mlir::LogicalResult CIRToLLVMGetMemberOpLowering::matchAndRewrite(
   }
 }
 
+mlir::LogicalResult CIRToLLVMUnreachableOpLowering::matchAndRewrite(
+    cir::UnreachableOp op, OpAdaptor adaptor,
+    mlir::ConversionPatternRewriter &rewriter) const {
+  rewriter.replaceOpWithNewOp<mlir::LLVM::UnreachableOp>(op);
+  return mlir::success();
+}
+
 mlir::LogicalResult CIRToLLVMTrapOpLowering::matchAndRewrite(
     cir::TrapOp op, OpAdaptor adaptor,
     mlir::ConversionPatternRewriter &rewriter) const {
diff --git a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
index f339d4310ae0c..c5106cb33f452 100644
--- a/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
+++ b/clang/lib/CIR/Lowering/DirectToLLVM/LowerToLLVM.h
@@ -402,6 +402,16 @@ class CIRToLLVMGetMemberOpLowering
                   mlir::ConversionPatternRewriter &) const override;
 };
 
+class CIRToLLVMUnreachableOpLowering
+    : public mlir::OpConversionPattern<cir::UnreachableOp> {
+public:
+  using mlir::OpConversionPattern<cir::UnreachableOp>::OpConversionPattern;
+
+  mlir::LogicalResult
+  matchAndRewrite(cir::UnreachableOp op, OpAdaptor,
+                  mlir::ConversionPatternRewriter &) const override;
+};
+
 class CIRToLLVMTrapOpLowering : public mlir::OpConversionPattern<cir::TrapOp> {
 public:
   using mlir::OpConversionPattern<cir::TrapOp>::OpConversionPattern;
diff --git a/clang/test/CIR/CodeGen/builtin_call.cpp b/clang/test/CIR/CodeGen/builtin_call.cpp
index d9a70683a4dbc..8465ea83d7875 100644
--- a/clang/test/CIR/CodeGen/builtin_call.cpp
+++ b/clang/test/CIR/CodeGen/builtin_call.cpp
@@ -166,3 +166,27 @@ void expect_prob(int x, int y) {
 // LLVM-NEXT:    %[[Y_LONG:.+]] = sext i32 %[[Y]] to i64
 // LLVM-NEXT:    %{{.+}} = call i64 @llvm.expect.with.probability.i64(i64 %[[X_LONG]], i64 %[[Y_LONG]], double 2.500000e-01)
 // LLVM:       }
+
+void unreachable() {
+  __builtin_unreachable();
+}
+
+// CIR-LABEL: @_Z11unreachablev
+// CIR:         cir.unreachable
+// CIR:       }
+
+// LLVM-LABEL: @_Z11unreachablev
+// LLVM:         unreachable
+// LLVM:       }
+
+void trap() {
+  __builtin_trap();
+}
+
+// CIR-LABEL: @_Z4trapv
+// CIR:         cir.trap
+// CIR:       }
+
+// LLVM-LABEL: @_Z4trapv
+// LLVM:         call void @llvm.trap()
+// LLVM:       }