Auto merge of #138759 - scottmcm:operand-builder, r=saethlin

Allow `enum` and `union` literals to also create SSA values

Today, `Some(x)` always goes through an `alloca`, even in trivial cases where the niching means the constructor doesn't even change the value.

For example, <https://rust.godbolt.org/z/6KG6PqoYz>
```rust
pub fn demo(r: &i32) -> Option<&i32> {
    Some(r)
}
```
currently emits the IR
```llvm
define align 4 ptr `@demo(ptr` align 4 %r) unnamed_addr {
start:
  %_0 = alloca [8 x i8], align 8
  store ptr %r, ptr %_0, align 8
  %0 = load ptr, ptr %_0, align 8
  ret ptr %0
}
```
but with this PR it becomes just
```llvm
define align 4 ptr `@demo(ptr` align 4 %r) unnamed_addr {
start:
  ret ptr %r
}
```
(Of course the optimizer can clean that up, but it'd be nice if it didn't have to -- especially in debug where it doesn't run.  This is like rust-lang/rust#123886, but that only handled non-simd `struct`s -- this PR generalizes it to all non-simd ADTs.)

Doing this means handing variants other than `FIRST_VARIANT`, handling the active field for unions, refactoring the discriminant code so the Place and Operand parts can share the calculation, etc.

Other PRs that led up to this one:
- https://github.com/rust-lang/rust/pull/142005
- https://github.com/rust-lang/rust/pull/142103
- https://github.com/rust-lang/rust/pull/142324
- https://github.com/rust-lang/rust/pull/142383

---

try-job: aarch64-gnu

1 files changed, 129 insertions, 0 deletions

diff --git a/tests/codegen/enum/enum-aggregate.rs b/tests/codegen/enum/enum-aggregate.rs
new file mode 100644
index 00000000000..b6a9b8dd814
--- /dev/null
+++ b/tests/codegen/enum/enum-aggregate.rs
@@ -0,0 +1,129 @@
+//@ compile-flags: -Copt-level=0 -Cno-prepopulate-passes
+//@ min-llvm-version: 19
+//@ only-64bit
+
+#![crate_type = "lib"]
+
+use std::cmp::Ordering;
+use std::num::NonZero;
+use std::ptr::NonNull;
+
+#[no_mangle]
+fn make_some_bool(x: bool) -> Option<bool> {
+    // CHECK-LABEL: i8 @make_some_bool(i1 zeroext %x)
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: %[[WIDER:.+]] = zext i1 %x to i8
+    // CHECK-NEXT: ret i8 %[[WIDER]]
+    Some(x)
+}
+
+#[no_mangle]
+fn make_none_bool() -> Option<bool> {
+    // CHECK-LABEL: i8 @make_none_bool()
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: ret i8 2
+    None
+}
+
+#[no_mangle]
+fn make_some_ordering(x: Ordering) -> Option<Ordering> {
+    // CHECK-LABEL: i8 @make_some_ordering(i8 %x)
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: ret i8 %x
+    Some(x)
+}
+
+#[no_mangle]
+fn make_some_u16(x: u16) -> Option<u16> {
+    // CHECK-LABEL: { i16, i16 } @make_some_u16(i16 %x)
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: %0 = insertvalue { i16, i16 } { i16 1, i16 poison }, i16 %x, 1
+    // CHECK-NEXT: ret { i16, i16 } %0
+    Some(x)
+}
+
+#[no_mangle]
+fn make_none_u16() -> Option<u16> {
+    // CHECK-LABEL: { i16, i16 } @make_none_u16()
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: ret { i16, i16 } { i16 0, i16 undef }
+    None
+}
+
+#[no_mangle]
+fn make_some_nzu32(x: NonZero<u32>) -> Option<NonZero<u32>> {
+    // CHECK-LABEL: i32 @make_some_nzu32(i32 %x)
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: ret i32 %x
+    Some(x)
+}
+
+#[no_mangle]
+fn make_ok_ptr(x: NonNull<u16>) -> Result<NonNull<u16>, usize> {
+    // CHECK-LABEL: { i64, ptr } @make_ok_ptr(ptr %x)
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: %0 = insertvalue { i64, ptr } { i64 0, ptr poison }, ptr %x, 1
+    // CHECK-NEXT: ret { i64, ptr } %0
+    Ok(x)
+}
+
+#[no_mangle]
+fn make_ok_int(x: usize) -> Result<usize, NonNull<u16>> {
+    // CHECK-LABEL: { i64, ptr } @make_ok_int(i64 %x)
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: %[[NOPROV:.+]] = getelementptr i8, ptr null, i64 %x
+    // CHECK-NEXT: %[[R:.+]] = insertvalue { i64, ptr } { i64 0, ptr poison }, ptr %[[NOPROV]], 1
+    // CHECK-NEXT: ret { i64, ptr } %[[R]]
+    Ok(x)
+}
+
+#[no_mangle]
+fn make_some_ref(x: &u16) -> Option<&u16> {
+    // CHECK-LABEL: ptr @make_some_ref(ptr align 2 %x)
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: ret ptr %x
+    Some(x)
+}
+
+#[no_mangle]
+fn make_none_ref<'a>() -> Option<&'a u16> {
+    // CHECK-LABEL: ptr @make_none_ref()
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: ret ptr null
+    None
+}
+
+#[inline(never)]
+fn make_err_generic<E>(e: E) -> Result<u32, E> {
+    // CHECK-LABEL: define{{.+}}make_err_generic
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: call void @llvm.trap()
+    // CHECK-NEXT: ret i32 poison
+    Err(e)
+}
+
+#[no_mangle]
+fn make_uninhabited_err_indirectly(n: Never) -> Result<u32, Never> {
+    // CHECK-LABEL: i32 @make_uninhabited_err_indirectly()
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: call{{.+}}make_err_generic
+    make_err_generic(n)
+}
+
+#[no_mangle]
+fn make_fully_uninhabited_result(v: u32, n: Never) -> Result<(u32, Never), (Never, u32)> {
+    // We don't try to do this in SSA form since the whole type is uninhabited.
+
+    // CHECK-LABEL: { i32, i32 } @make_fully_uninhabited_result(i32 %v)
+    // CHECK: %[[ALLOC_V:.+]] = alloca [4 x i8]
+    // CHECK: %[[RET:.+]] = alloca [8 x i8]
+    // CHECK: store i32 %v, ptr %[[ALLOC_V]]
+    // CHECK: %[[TEMP_V:.+]] = load i32, ptr %[[ALLOC_V]]
+    // CHECK: %[[INNER:.+]] = getelementptr inbounds i8, ptr %[[RET]]
+    // CHECK: store i32 %[[TEMP_V]], ptr %[[INNER]]
+    // CHECK: call void @llvm.trap()
+    // CHECK: unreachable
+    Ok((v, n))
+}
+
+enum Never {}