explicitly include muloti4 in LLVM IR

compiler/builtins/bitcode/build.zig

@@ -39,7 +39,7 @@ pub fn build(b: *Builder) void {
     obj.linkSystemLibrary("c");
     obj.setOutputDir(".");
     obj.strip = true;
-    // obj.bundle_compiler_rt = true;
+    obj.bundle_compiler_rt = true;
     const obj_step = b.step("object", "Build object file for linking");
     obj_step.dependOn(&obj.step);
 

compiler/builtins/bitcode/src/main.zig

@@ -131,3 +131,46 @@ pub fn panic(message: []const u8, stacktrace: ?*std.builtin.StackTrace) noreturn
 test "" {
     testing.refAllDecls(@This());
 }
+
+export fn __muloti4(a: i128, b: i128, overflow: *c_int) callconv(.C) i128 {
+    // @setRuntimeSafety(builtin.is_test);
+
+    const min = @bitCast(i128, @as(u128, 1 << (128 - 1)));
+    const max = ~min;
+    overflow.* = 0;
+
+    const r = a *% b;
+    if (a == min) {
+        if (b != 0 and b != 1) {
+            overflow.* = 1;
+        }
+        return r;
+    }
+    if (b == min) {
+        if (a != 0 and a != 1) {
+            overflow.* = 1;
+        }
+        return r;
+    }
+
+    const sa = a >> (128 - 1);
+    const abs_a = (a ^ sa) -% sa;
+    const sb = b >> (128 - 1);
+    const abs_b = (b ^ sb) -% sb;
+
+    if (abs_a < 2 or abs_b < 2) {
+        return r;
+    }
+
+    if (sa == sb) {
+        if (abs_a > @divTrunc(max, abs_b)) {
+            overflow.* = 1;
+        }
+    } else {
+        if (abs_a > @divTrunc(min, -abs_b)) {
+            overflow.* = 1;
+        }
+    }
+
+    return r;
+}

compiler/gen_llvm/src/llvm/build.rs

@@ -369,6 +369,10 @@ fn add_intrinsics<'ctx>(ctx: &'ctx Context, module: &Module<'ctx>) {
     let i32_type = ctx.i32_type();
     let i64_type = ctx.i64_type();
 
+    if let Some(func) = module.get_function("__muloti4") {
+        func.set_linkage(Linkage::External);
+    }
+
     add_intrinsic(
         module,
         LLVM_LOG_F64,