Auto merge of #104535 - mikebenfield:discr-fix, r=pnkfelix

rustc_codegen_ssa: Fix for codegen_get_discr

When doing the optimized implementation of getting the discriminant, the arithmetic needs to be done in the tag type so wrapping behavior works correctly.

Fixes #104519

2 files changed, 38 insertions, 5 deletions

diff --git a/src/test/codegen/enum-match.rs b/src/test/codegen/enum-match.rs
index efab189fd7b..44f1b408d21 100644
--- a/src/test/codegen/enum-match.rs
+++ b/src/test/codegen/enum-match.rs
@@ -34,11 +34,8 @@ pub enum Enum1 {
 
 // CHECK: define i8 @match1{{.*}}
 // CHECK-NEXT: start:
-// CHECK-NEXT: %1 = icmp ugt i8 %0, 1
-// CHECK-NEXT: %2 = zext i8 %0 to i64
-// CHECK-NEXT: %3 = add nsw i64 %2, -1
-// CHECK-NEXT: %_2 = select i1 %1, i64 %3, i64 0
-// CHECK-NEXT: switch i64 %_2, label {{.*}} [
+// CHECK-NEXT: %1 = {{.*}}call i8 @llvm.usub.sat.i8(i8 %0, i8 1)
+// CHECK-NEXT: switch i8 %1, label {{.*}} [
 #[no_mangle]
 pub fn match1(e: Enum1) -> u8 {
     use Enum1::*;
diff --git a/src/test/ui/enum-discriminant/issue-104519.rs b/src/test/ui/enum-discriminant/issue-104519.rs
new file mode 100644
index 00000000000..c4630f76b3a
--- /dev/null
+++ b/src/test/ui/enum-discriminant/issue-104519.rs
@@ -0,0 +1,36 @@
+// run-pass
+#![allow(dead_code)]
+
+enum OpenResult {
+    Ok(()),
+    Err(()),
+    TransportErr(TransportErr),
+}
+
+#[repr(i32)]
+enum TransportErr {
+    UnknownMethod = -2,
+}
+
+#[inline(never)]
+fn some_match(result: OpenResult) -> u8 {
+    match result {
+        OpenResult::Ok(()) => 0,
+        _ => 1,
+    }
+}
+
+fn main() {
+    let result = OpenResult::Ok(());
+    assert_eq!(some_match(result), 0);
+
+    let result = OpenResult::Ok(());
+    match result {
+        OpenResult::Ok(()) => (),
+        _ => unreachable!("message a"),
+    }
+    match result {
+        OpenResult::Ok(()) => (),
+        _ => unreachable!("message b"),
+    }
+}