Auto merge of #126852 - scottmcm:more-checked-math-tweaks, r=Amanieu

Also get `add nuw` from `uN::checked_add`

When I was doing this for `checked_{sub,shl,shr}`, it was mentioned https://github.com/rust-lang/rust/pull/124114#issuecomment-2066173305 that it'd be worth trying for `checked_add` too.

It makes a particularly-big difference for `x.checked_add(C)`, as doing this means that LLVM removes the intrinsic and does it as a normal `x <= MAX - C` instead.

cc `@DianQK` who had commented about `checked_add` related to https://github.com/rust-lang/hashbrown/issues/509 before

cc https://github.com/llvm/llvm-project/issues/80637 for how LLVM is unlikely to do this itself

1 files changed, 14 insertions, 0 deletions

diff --git a/tests/codegen/checked_math.rs b/tests/codegen/checked_math.rs
index 41016e3b7be..75df5866d6e 100644
--- a/tests/codegen/checked_math.rs
+++ b/tests/codegen/checked_math.rs
@@ -84,3 +84,17 @@ pub fn checked_shr_signed(a: i32, b: u32) -> Option<i32> {
     // CHECK: ret { i32, i32 } %[[R1]]
     a.checked_shr(b)
 }
+
+// CHECK-LABEL: @checked_add_one_unwrap_unsigned
+// CHECK-SAME: (i32 noundef %x)
+#[no_mangle]
+pub fn checked_add_one_unwrap_unsigned(x: u32) -> u32 {
+    // CHECK: %[[IS_MAX:.+]] = icmp eq i32 %x, -1
+    // CHECK: br i1 %[[IS_MAX]], label %[[NONE_BB:.+]], label %[[SOME_BB:.+]]
+    // CHECK: [[SOME_BB]]:
+    // CHECK: %[[R:.+]] = add nuw i32 %x, 1
+    // CHECK: ret i32 %[[R]]
+    // CHECK: [[NONE_BB]]:
+    // CHECK: call {{.+}}unwrap_failed
+    x.checked_add(1).unwrap()
+}