add tests related to tuple scalar layout with ZST in last field

src/test/codegen/tuple-layout-opt.rs

@@ -0,0 +1,36 @@
+// ignore-emscripten
+// compile-flags: -C no-prepopulate-passes
+
+// Test that tuples get optimized layout, in particular with a ZST in the last field (#63244)
+
+#![crate_type="lib"]
+
+type ScalarZstLast = (u128, ());
+// CHECK: define i128 @test_ScalarZstLast(i128 %_1)
+#[no_mangle]
+pub fn test_ScalarZstLast(_: ScalarZstLast) -> ScalarZstLast { loop {} }
+
+type ScalarZstFirst = ((), u128);
+// CHECK: define i128 @test_ScalarZstFirst(i128 %_1)
+#[no_mangle]
+pub fn test_ScalarZstFirst(_: ScalarZstFirst) -> ScalarZstFirst { loop {} }
+
+type ScalarPairZstLast = (u8, u128, ());
+// CHECK: define { i128, i8 } @test_ScalarPairZstLast(i128 %_1.0, i8 %_1.1)
+#[no_mangle]
+pub fn test_ScalarPairZstLast(_: ScalarPairZstLast) -> ScalarPairZstLast { loop {} }
+
+type ScalarPairZstFirst = ((), u8, u128);
+// CHECK: define { i8, i128 } @test_ScalarPairZstFirst(i8 %_1.0, i128 %_1.1)
+#[no_mangle]
+pub fn test_ScalarPairZstFirst(_: ScalarPairZstFirst) -> ScalarPairZstFirst { loop {} }
+
+type ScalarPairLotsOfZsts = ((), u8, (), u128, ());
+// CHECK: define { i128, i8 } @test_ScalarPairLotsOfZsts(i128 %_1.0, i8 %_1.1)
+#[no_mangle]
+pub fn test_ScalarPairLotsOfZsts(_: ScalarPairLotsOfZsts) -> ScalarPairLotsOfZsts { loop {} }
+
+type ScalarPairLottaNesting = (((), ((), u8, (), u128, ())), ());
+// CHECK: define { i128, i8 } @test_ScalarPairLottaNesting(i128 %_1.0, i8 %_1.1)
+#[no_mangle]
+pub fn test_ScalarPairLottaNesting(_: ScalarPairLottaNesting) -> ScalarPairLottaNesting { loop {} }

src/test/ui/dynamically-sized-types/dst-tuple-no-reorder.rs

@@ -0,0 +1,26 @@
+// run-pass
+
+#![feature(unsized_tuple_coercion)]
+
+// Ensure that unsizable fields that might be accessed don't get reordered
+
+fn nonzero_size() {
+    let sized: (u8, [u32; 2]) = (123, [456, 789]);
+    let unsize: &(u8, [u32]) = &sized;
+    assert_eq!(unsize.0, 123);
+    assert_eq!(unsize.1.len(), 2);
+    assert_eq!(unsize.1[0], 456);
+    assert_eq!(unsize.1[1], 789);
+}
+
+fn zst() {
+    let sized: (u8, [u32; 0]) = (123, []);
+    let unsize: &(u8, [u32]) = &sized;
+    assert_eq!(unsize.0, 123);
+    assert_eq!(unsize.1.len(), 0);
+}
+
+pub fn main() {
+    nonzero_size();
+    zst();
+}

src/test/ui/mir/mir_const_prop_tuple_field_reorder.rs

@@ -0,0 +1,27 @@
+// compile-flags: -Z mir-opt-level=2
+// build-pass
+#![crate_type="lib"]
+
+// This used to ICE: const-prop did not account for field reordering of scalar pairs,
+// and would generate a tuple like `(0x1337, VariantBar): (FooEnum, isize)`,
+// causing assertion failures in codegen when trying to read 0x1337 at the wrong type.
+
+pub enum FooEnum {
+    VariantBar,
+    VariantBaz,
+    VariantBuz,
+}
+
+pub fn wrong_index() -> isize {
+    let (_, b) = id((FooEnum::VariantBar, 0x1337));
+    b
+}
+
+pub fn wrong_index_two() -> isize {
+    let (_, (_, b)) = id(((), (FooEnum::VariantBar, 0x1338)));
+    b
+}
+
+fn id<T>(x: T) -> T {
+    x
+}