From d27f0faecf4741734cc3dfe8d6c504f4705d327e Mon Sep 17 00:00:00 2001
From: Sid Nayyar <sidnayyar@google.com>
Date: Mon, 20 May 2024 12:19:52 +0100
Subject: rust: add test where discriminant is offset from beginning in the
 variant data layout

This is an optimisation which the Rust compiler can make by overlapping
the discriminant with variant members data locations while exploiting
bit patterns which would be illegal for the variant members.

PiperOrigin-RevId: 635414233
Change-Id: I5da9db7326dfea4756b8edebd19fa8e6c30ea30a
---
 .../expected/offset_discriminant_rs.elf_stg        | 106 +++++++++++++++++++++
 .../info_tests/variant/offset_discriminant.rs      |  13 +++
 2 files changed, 119 insertions(+)
 create mode 100644 test_cases/info_tests/variant/expected/offset_discriminant_rs.elf_stg
 create mode 100644 test_cases/info_tests/variant/offset_discriminant.rs

diff --git a/test_cases/info_tests/variant/expected/offset_discriminant_rs.elf_stg b/test_cases/info_tests/variant/expected/offset_discriminant_rs.elf_stg
new file mode 100644
index 0000000..e7ab069
--- /dev/null
+++ b/test_cases/info_tests/variant/expected/offset_discriminant_rs.elf_stg
@@ -0,0 +1,106 @@
+version: 0x00000002
+root_id: 0x84ea5130  # interface
+primitive {
+  id: 0x384f7d7c
+  name: "char"
+  encoding: UTF
+  bytesize: 0x00000004
+}
+primitive {
+  id: 0x62aebfd4
+  name: "bool"
+  encoding: BOOLEAN
+  bytesize: 0x00000001
+}
+primitive {
+  id: 0xd4bacb77
+  name: "u32"
+  encoding: UNSIGNED_INTEGER
+  bytesize: 0x00000004
+}
+member {
+  id: 0x16e523e2
+  type_id: 0xd4bacb77  # u32
+  offset: 32
+}
+member {
+  id: 0x97813cf0
+  name: "__0"
+  type_id: 0x384f7d7c  # char
+}
+member {
+  id: 0xdbc0cd2f
+  name: "__1"
+  type_id: 0x384f7d7c  # char
+  offset: 32
+}
+variant_member {
+  id: 0x56b9f935
+  name: "Two"
+  type_id: 0x573dc947
+}
+variant_member {
+  id: 0x69cfc441
+  name: "One"
+  discriminant_value: 1114112
+  type_id: 0x988e2459
+}
+variant_member {
+  id: 0x276cfc01
+  name: "Zero"
+  discriminant_value: 1114113
+  type_id: 0xb2cd8432
+}
+struct_union {
+  id: 0x988e2459
+  kind: STRUCT
+  name: "offset_discriminant::Foo::One"
+  definition {
+    bytesize: 8
+    member_id: 0x97813cf0  # char __0
+  }
+}
+struct_union {
+  id: 0x573dc947
+  kind: STRUCT
+  name: "offset_discriminant::Foo::Two"
+  definition {
+    bytesize: 8
+    member_id: 0x97813cf0  # char __0
+    member_id: 0xdbc0cd2f  # char __1
+  }
+}
+struct_union {
+  id: 0xb2cd8432
+  kind: STRUCT
+  name: "offset_discriminant::Foo::Zero"
+  definition {
+    bytesize: 8
+  }
+}
+variant {
+  id: 0x82b2aa29
+  name: "offset_discriminant::Foo"
+  bytesize: 8
+  discriminant: 0x16e523e2
+  member_id: 0x56b9f935
+  member_id: 0x69cfc441
+  member_id: 0x276cfc01
+}
+function {
+  id: 0x9efcc134
+  return_type_id: 0x62aebfd4  # bool
+  parameter_id: 0x82b2aa29  # variant offset_discriminant::Foo
+}
+elf_symbol {
+  id: 0x699cebd9
+  name: "is_zero"
+  is_defined: true
+  symbol_type: FUNCTION
+  type_id: 0x9efcc134  # bool(variant offset_discriminant::Foo)
+  full_name: "offset_discriminant::is_zero"
+}
+interface {
+  id: 0x84ea5130
+  symbol_id: 0x699cebd9  # bool offset_discriminant::is_zero(variant offset_discriminant::Foo)
+}
diff --git a/test_cases/info_tests/variant/offset_discriminant.rs b/test_cases/info_tests/variant/offset_discriminant.rs
new file mode 100644
index 0000000..a7aca13
--- /dev/null
+++ b/test_cases/info_tests/variant/offset_discriminant.rs
@@ -0,0 +1,13 @@
+pub enum Foo {
+    Two(char, char),
+    One(char),
+    Zero,
+}
+
+#[no_mangle]
+pub fn is_zero(foo: Foo) -> bool {
+    match foo {
+        Foo::Zero => true,
+        _ => false,
+    }
+}
-- 
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