test(codegen): Add and update codegen tests for DST size_of_val assume

Co-authored-by: Scott McMurray <scottmcm@users.noreply.github.com>

Author: TKanX

tests/codegen-llvm/dst-size-of-val-not-zst.rs

@@ -0,0 +1,30 @@
+//@ compile-flags: -Copt-level=3 -Z merge-functions=disabled
+//@ needs-deterministic-layouts
+
+#![crate_type = "lib"]
+
+// Regression test for #152788: `size_of_val(p) == 0` folds to `false` for
+// DSTs with a non-zero prefix (nuw+nsw on offset+tail, assume on rounding).
+
+pub struct Foo<T: ?Sized>(pub [u32; 3], pub T);
+
+// CHECK-LABEL: @size_of_val_dyn_not_zero
+#[no_mangle]
+pub fn size_of_val_dyn_not_zero(p: &Foo<dyn std::fmt::Debug>) -> bool {
+    // CHECK: ret i1 false
+    std::mem::size_of_val(p) == 0
+}
+
+// CHECK-LABEL: @size_of_val_slice_u8_not_zero
+#[no_mangle]
+pub fn size_of_val_slice_u8_not_zero(p: &Foo<[u8]>) -> bool {
+    // CHECK: ret i1 false
+    std::mem::size_of_val(p) == 0
+}
+
+// CHECK-LABEL: @size_of_val_slice_i32_not_zero
+#[no_mangle]
+pub fn size_of_val_slice_i32_not_zero(p: &Foo<[i32]>) -> bool {
+    // CHECK: ret i1 false
+    std::mem::size_of_val(p) == 0
+}