test merging of multiple match branches that access fields of the sam…

…e offset

tests/codegen/issues/issue-121719-common-field-offset.rs

@@ -0,0 +1,44 @@
+//! This test checks that match branches which all access a field
+//! at the same offset are merged together.
+//!
+//@ compile-flags: -O
+#![crate_type = "lib"]
+
+#[repr(C)]
+pub struct A {
+    x: f64,
+    y: u64,
+}
+#[repr(C)]
+pub struct B {
+    x: f64,
+    y: u32,
+}
+#[repr(C)]
+pub struct C {
+    x: f64,
+    y: u16,
+}
+#[repr(C)]
+pub struct D {
+    x: f64,
+    y: u8,
+}
+
+pub enum E {
+    A(A),
+    B(B),
+    C(C),
+    D(D),
+}
+
+// CHECK-LABEL: @match_on_e
+#[no_mangle]
+pub fn match_on_e(e: &E) -> &f64 {
+    // CHECK: start:
+    // CHECK-NEXT: getelementptr
+    // CHECK-NEXT: ret
+    match e {
+        E::A(A { x, .. }) | E::B(B { x, .. }) | E::C(C { x, .. }) | E::D(D { x, .. }) => x,
+    }
+}