diff --git a/src/bin/build-llvm.ts b/src/bin/build-llvm.ts
index 11737b9..57f17fa 100644
--- a/src/bin/build-llvm.ts
+++ b/src/bin/build-llvm.ts
@@ -5,8 +5,10 @@ import path from 'path';
 import { buildPackage } from '../build/build.js';
 import { randomUUID } from 'crypto';
 import { arch } from 'os';
+import * as sunway from '../sunway.js';
+import chalk from 'chalk';
 
-const args = await yargs(hideBin(process.argv))
+const argv = await yargs(hideBin(process.argv))
     .version("0.0.0")
     .option("src", {
         describe: "Source directory to llvm-project",
@@ -21,20 +23,31 @@ const args = await yargs(hideBin(process.argv))
         describe: "Install prefix",
         type: "string",
     })
-    .option("msimd-math", {
+    .option("math-simd", {
         describe: "Add -msimd for libpgmath",
         type: "boolean",
         demandOption: true,
     })
+    .option('mcpu', {
+        type: 'string',
+        description: '-mcpu option for compilers',
+        choices: ['8a', '6b', 'host'],
+        default: 'host',
+    })
     .help()
     .parse();
 
-const src = path.resolve(args.src);
-const build = args.build ?? path.resolve(src, "build");
-const prefix = args.prefix ?? path.resolve(src, "install", randomUUID());
+const src = path.resolve(argv.src);
+const build = argv.build ?? path.resolve(src, "build");
+const prefix = argv.prefix ?? path.resolve(src, "install", randomUUID());
+
+const cpuVariant = argv.mcpu === "host" ? sunway.getHostGeneration() : argv.platform as sunway.SunwayGeneration;
+
+console.log(`prefix: ${chalk.red(prefix)}`);
+console.log(`mcpu: ${cpuVariant}`);
 
 const packages = llvmPackages({
-    src: args.src,
+    src: argv.src,
     buildDir(packageName) {
         return path.join(build, packageName);
     },
@@ -44,7 +57,8 @@ const packages = llvmPackages({
         buildPlatform: { arch: arch() },
         hostPlatform: { arch: arch() },
     },
-    enableLibpgmathSIMD: args['msimd-math']
+    mathSIMD: argv['math-simd'],
+    cpuVariant,
 });
 
 for (const pkg of packages) {
diff --git a/src/build/llvmPackages.ts b/src/build/llvmPackages.ts
index 8ab4b94..670523c 100644
--- a/src/build/llvmPackages.ts
+++ b/src/build/llvmPackages.ts
@@ -1,9 +1,10 @@
 import path from "path";
-import { GeneralVariable, LLVMVariable, command, variable } from "../commands/cmake.js";
+import { GeneralVariable, LLVMVariable, buildCompilerFlags, command, variable } from "../commands/cmake.js";
 import { PackagePlatform, PackageTask } from "./build.js";
 import { promisifySpawn } from "../cli.js";
 import os from "os";
 import { SpawnOptions, spawn } from "child_process";
+import * as sunway from '../sunway.js';
 
 export interface LLVMPackageOverrides {
     cmakeDefinitionOverrides?: {
@@ -60,7 +61,9 @@ export interface LLVMPackageOptions {
 
     platform: PackagePlatform;
 
-    enableLibpgmathSIMD: boolean;
+    mathSIMD: boolean;
+
+    cpuVariant: sunway.SunwayGeneration;
 };
 
 export function llvmPackages({
@@ -70,7 +73,8 @@ export function llvmPackages({
     buildDir,
     cmakeDefinitionOverrides,
     spawnOverrides,
-    enableLibpgmathSIMD = false,
+    mathSIMD,
+    cpuVariant,
 }: LLVMPackageOptions & LLVMPackageOverrides): PackageTask[] {
     const rm = "rm";
     const cmake = "cmake";
@@ -107,6 +111,16 @@ export function llvmPackages({
         await promisifySpawn(spawn(cmake, ["--build", build, "--target", "install"], spawnOptions));
     });
 
+    const mcpuFlag = sunway.mcpu(cpuVariant);
+
+    // Shared flags for compiling libpgmath & cflang.
+    // The toolchain of these targets are clang.
+    const clangCXFlags = [
+        "-Wno-sign-compare",
+        mcpuFlag,
+    ];
+
+
     function mkLLVMPackage(): PackageTask {
         const build = buildDir('llvm');
         return {
@@ -139,18 +153,19 @@ export function llvmPackages({
                 await promisifySpawn(spawn(rm, ["-rf", build], spawnOptions));
 
                 // Flags shared between C and C++ compiler.
-                const cxFlags = ["-mlong-double-64"];
-                if (enableLibpgmathSIMD) {
-                    cxFlags.push("-msimd");
-                }
+                const cxFlags = [
+                    ...clangCXFlags,
+                    "-mlong-double-64",
+                    ...mathSIMD ? ["-msimd"] : [],
+                ];
 
                 // Configure libpgmath.
                 await promisifySpawn(spawn(cmake, command({
                     definitions: variable({
                         ...general,
                         ...{
-                            CMAKE_C_FLAGS: cxFlags.join(" "),
-                            CMAKE_CXX_FLAGS: cxFlags.join(" "),
+                            CMAKE_C_FLAGS: buildCompilerFlags(cxFlags),
+                            CMAKE_CXX_FLAGS: buildCompilerFlags(cxFlags),
                             CMAKE_C_COMPILER: path.join(installPrefix, "bin", "clang"),
                             CMAKE_CXX_COMPILER: path.join(installPrefix, "bin", "clang++"),
                         } as GeneralVariable,
@@ -172,12 +187,17 @@ export function llvmPackages({
             name: "cflang",
             configurePhase: async () => {
                 await promisifySpawn(spawn(rm, ["-rf", build], spawnOptions));
-
+                const cxFlags = [
+                    ...clangCXFlags,
+                ];
                 // Configure cflang.
                 await promisifySpawn(spawn(cmake, command({
                     definitions: variable({
                         ...general,
                         ...{
+                            CMAKE_C_FLAGS: buildCompilerFlags(cxFlags),
+                            CMAKE_CXX_FLAGS: buildCompilerFlags(cxFlags),
+                            CMAKE_Fortran_FLAGS: buildCompilerFlags([mcpuFlag]),
                             CMAKE_C_COMPILER: path.join(installPrefix, "bin", "clang"),
                             CMAKE_CXX_COMPILER: path.join(installPrefix, "bin", "clang++"),
                             CMAKE_Fortran_COMPILER: path.join(installPrefix, "bin", "flang"),
diff --git a/src/commands/cmake.ts b/src/commands/cmake.ts
index 63db717..4117697 100644
--- a/src/commands/cmake.ts
+++ b/src/commands/cmake.ts
@@ -130,3 +130,27 @@ export function command(o: CMakeGenerateOptions): string[] {
         ...optFlag('-C', o.preloadCache),
     ];
 }
+
+
+/**
+ * Escapes a single C compiler flag argument to ensure CMake can parse it correctly.
+ * Handles spaces and double quotes by wrapping the argument in double quotes and escaping internal double quotes.
+ */
+function escapeCmakeFlag(arg: string): string {
+    // Escape internal double quotes as \"
+    let escaped = arg.replace(/"/g, '\\"');
+    // If the argument contains spaces or originally has double quotes, wrap it in double quotes
+    if (escaped.includes(' ') || arg.includes('"')) {
+        escaped = `"${escaped}"`;
+    }
+    return escaped;
+}
+
+/**
+ * Converts an array of strings into a single string suitable for CMAKE_C_FLAGS.
+ * @param flags The original array of compiler flags, e.g., ["-O2", "-DNAME=Hello World"]
+ * @returns The escaped string that can be directly passed to CMake
+ */
+export function buildCompilerFlags(flags: string[]): string {
+    return flags.map(escapeCmakeFlag).join(' ');
+}
\ No newline at end of file