Use a C-safe return type for __rust_[ui]128_* overflowing intrinsics

Most of our Rust-specific overflowing intrinsics currently return
`(i128, bool)`, which is not guaranteed to have a stable ABI. Switch to
returning the overflow via a mutable parameter and only directly
returning the integer result.

`__rust_i128_mulo` now matches the function signature of `__muloti4`,
but they do not share the same ABI on Windows so we cannot easily
deduplicate them.

src/int/addsub.rs

@@ -66,31 +66,39 @@ intrinsics! {
         AddSub::add(a,b)
     }
 
-    pub extern "C" fn __rust_i128_addo(a: i128, b: i128) -> (i128, bool) {
-        a.addo(b)
+    pub extern "C" fn __rust_i128_addo(a: i128, b: i128, oflow: &mut i32) -> i128 {
+        let (add, o) = a.addo(b);
+        *oflow = o.into();
+        add
     }
 
     pub extern "C" fn __rust_u128_add(a: u128, b: u128) -> u128 {
         AddSub::add(a,b)
     }
 
-    pub extern "C" fn __rust_u128_addo(a: u128, b: u128) -> (u128, bool) {
-        a.addo(b)
+    pub extern "C" fn __rust_u128_addo(a: u128, b: u128, oflow: &mut i32) -> u128 {
+        let (add, o) = a.addo(b);
+        *oflow = o.into();
+        add
     }
 
     pub extern "C" fn __rust_i128_sub(a: i128, b: i128) -> i128 {
         AddSub::sub(a,b)
     }
 
-    pub extern "C" fn __rust_i128_subo(a: i128, b: i128) -> (i128, bool) {
-        a.subo(b)
+    pub extern "C" fn __rust_i128_subo(a: i128, b: i128, oflow: &mut i32) -> i128 {
+        let (sub, o) = a.subo(b);
+        *oflow = o.into();
+        sub
     }
 
     pub extern "C" fn __rust_u128_sub(a: u128, b: u128) -> u128 {
         AddSub::sub(a,b)
     }
 
-    pub extern "C" fn __rust_u128_subo(a: u128, b: u128) -> (u128, bool) {
-        a.subo(b)
+    pub extern "C" fn __rust_u128_subo(a: u128, b: u128, oflow: &mut i32) -> u128 {
+        let (sub, o) = a.subo(b);
+        *oflow = o.into();
+        sub
     }
 }

src/int/mul.rs

@@ -128,11 +128,15 @@ intrinsics! {
         mul
     }
 
-    pub extern "C" fn __rust_i128_mulo(a: i128, b: i128) -> (i128, bool) {
-        i128_overflowing_mul(a, b)
+    pub extern "C" fn __rust_i128_mulo(a: i128, b: i128, oflow: &mut i32) -> i128 {
+        let (mul, o) = i128_overflowing_mul(a, b);
+        *oflow = o.into();
+        mul
     }
 
-    pub extern "C" fn __rust_u128_mulo(a: u128, b: u128) -> (u128, bool) {
-        a.mulo(b)
+    pub extern "C" fn __rust_u128_mulo(a: u128, b: u128, oflow: &mut i32) -> u128 {
+        let (mul, o) = a.mulo(b);
+        *oflow = o.into();
+        mul
     }
 }

testcrate/tests/addsub.rs

@@ -44,20 +44,22 @@ mod int_addsub {
                     use compiler_builtins::int::addsub::{$fn_add, $fn_sub};
 
                     fuzz_2(N, |x: $i, y: $i| {
-                        let add0 = x.overflowing_add(y);
-                        let sub0 = x.overflowing_sub(y);
-                        let add1: ($i, bool) = $fn_add(x, y);
-                        let sub1: ($i, bool) = $fn_sub(x, y);
-                        if add0.0 != add1.0 || add0.1 != add1.1 {
+                        let (add0, add_o0)= x.overflowing_add(y);
+                        let (sub0, sub_o0)= x.overflowing_sub(y);
+                        let mut add_o1 = 0;
+                        let mut sub_o1 = 0;
+                        let add1: $i = $fn_add(x, y, &mut add_o1);
+                        let sub1: $i = $fn_sub(x, y, &mut sub_o1);
+                        if add0 != add1 || i32::from(add_o0) != add_o1 {
                             panic!(
                                 "{}({}, {}): std: {:?}, builtins: {:?}",
-                                stringify!($fn_add), x, y, add0, add1
+                                stringify!($fn_add), x, y, (add0, add_o0) , (add1, add_o1)
                             );
                         }
-                        if sub0.0 != sub1.0 || sub0.1 != sub1.1 {
+                        if sub0 != sub1 || i32::from(sub_o0) != sub_o1 {
                             panic!(
                                 "{}({}, {}): std: {:?}, builtins: {:?}",
-                                stringify!($fn_sub), x, y, sub0, sub1
+                                stringify!($fn_sub), x, y, (sub0, sub_o0) , (sub1, sub_o1)
                             );
                         }
                     });

testcrate/tests/mul.rs

@@ -73,9 +73,10 @@ mod int_overflowing_mul {
         use compiler_builtins::int::mul::{__rust_i128_mulo, __rust_u128_mulo};
 
         fuzz_2(N, |x: u128, y: u128| {
+            let mut o1 = 0;
             let (mul0, o0) = x.overflowing_mul(y);
-            let (mul1, o1) = __rust_u128_mulo(x, y);
-            if mul0 != mul1 || o0 != o1 {
+            let mul1 = __rust_u128_mulo(x, y, &mut o1);
+            if mul0 != mul1 || i32::from(o0) != o1 {
                 panic!(
                     "__rust_u128_mulo({}, {}): std: ({}, {}), builtins: ({}, {})",
                     x, y, mul0, o0, mul1, o1
@@ -84,8 +85,8 @@ mod int_overflowing_mul {
             let x = x as i128;
             let y = y as i128;
             let (mul0, o0) = x.overflowing_mul(y);
-            let (mul1, o1) = __rust_i128_mulo(x, y);
-            if mul0 != mul1 || o0 != o1 {
+            let mul1 = __rust_i128_mulo(x, y, &mut o1);
+            if mul0 != mul1 || i32::from(o0) != o1 {
                 panic!(
                     "__rust_i128_mulo({}, {}): std: ({}, {}), builtins: ({}, {})",
                     x, y, mul0, o0, mul1, o1