Add __divmodti4

Author: AaronKutch

src/int/sdiv.rs

@@ -54,5 +54,12 @@ intrinsics! {
         i128_div_rem(a, b).1
     }
 
-    // LLVM does not currently have a `__divmodti4` function
+    // LLVM does not currently have a `__divmodti4` function, but GCC does
+    #[maybe_use_optimized_c_shim]
+    /// Returns `n / d` and sets `*rem = n % d`
+    pub extern "C" fn __divmodti4(a: i128, b: i128, rem: &mut i128) -> i128 {
+        let quo_rem = i128_div_rem(a, b);
+        *rem = quo_rem.1;
+        quo_rem.0
+    }
 }

testcrate/build.rs

@@ -805,6 +805,19 @@ fn main() {
             (builtins::int::sdiv::__divmodsi4(a, b, &mut r), r)
         }",
     );
+    gen(
+        |(a, b): (MyI128, MyI128)| {
+            if b.0 == 0 {
+                None
+            } else {
+                Some((a.0 / b.0, a.0 % b.0))
+            }
+        },
+        "{
+            let mut r = 0;
+            (builtins::int::sdiv::__divmodti4(a, b, &mut r), r)
+        }",
+    );
     gen(
         |(a, b): (MyI32, MyI32)| {
             if b.0 == 0 {

testcrate/tests/div_rem.rs

@@ -1,15 +1,9 @@
 use rand_xoshiro::rand_core::{RngCore, SeedableRng};
 use rand_xoshiro::Xoshiro128StarStar;
 
-use compiler_builtins::int::sdiv::{__divmoddi4, __divmodsi4, __divti3, __modti3};
+use compiler_builtins::int::sdiv::{__divmoddi4, __divmodsi4, __divmodti4};
 use compiler_builtins::int::udiv::{__udivmoddi4, __udivmodsi4, __udivmodti4};
 
-// because `__divmodti4` does not exist, we synthesize it
-fn __divmodti4(a: i128, b: i128, rem: &mut i128) -> i128 {
-    *rem = __modti3(a, b);
-    __divti3(a, b)
-}
-
 /// Creates intensive test functions for division functions of a certain size
 macro_rules! test {
     (