Support repr(simd) on ADTs containing a single array field

This PR allows using `#[repr(simd)]` on ADTs containing a
single array field:

```rust
 #[repr(simd)] struct S0([f32; 4]);
 #[repr(simd)] struct S1<const N: usize>([f32; N]);
 #[repr(simd)] struct S2<T, const N: usize>([T; N]);
```

This should allow experimenting with portable packed SIMD
abstractions on nightly that make use of const generics.

2 files changed, 91 insertions, 0 deletions

diff --git a/src/test/codegen/simd-intrinsic/simd-intrinsic-generic-extract-insert.rs b/src/test/codegen/simd-intrinsic/simd-intrinsic-generic-extract-insert.rs
new file mode 100644
index 00000000000..3dba044d376
--- /dev/null
+++ b/src/test/codegen/simd-intrinsic/simd-intrinsic-generic-extract-insert.rs
@@ -0,0 +1,47 @@
+// compile-flags: -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+
+#![feature(repr_simd, platform_intrinsics, const_generics)]
+#![allow(non_camel_case_types, incomplete_features)]
+
+#[repr(simd)]
+#[derive(Copy, Clone)]
+pub struct M(pub f32, pub f32, pub f32, pub f32);
+
+#[repr(simd)]
+#[derive(Copy, Clone)]
+pub struct S<const N: usize>([f32; N]);
+
+extern "platform-intrinsic" {
+    fn simd_extract<T, U>(x: T, idx: u32) -> U;
+    fn simd_insert<T, U>(x: T, idx: u32, b: U) -> T;
+}
+
+// CHECK-LABEL: @extract_m
+#[no_mangle]
+pub unsafe fn extract_m(v: M, i: u32) -> f32  {
+    // CHECK: extractelement <4 x float> %0, i32 %i
+    simd_extract(v, i)
+}
+
+// CHECK-LABEL: @extract_s
+#[no_mangle]
+pub unsafe fn extract_s(v: S<4>, i: u32) -> f32  {
+    // CHECK: extractelement <4 x float> %0, i32 %i
+    simd_extract(v, i)
+}
+
+// CHECK-LABEL: @insert_m
+#[no_mangle]
+pub unsafe fn insert_m(v: M, i: u32, j: f32) -> M  {
+    // CHECK: insertelement <4 x float> %1, float %j, i32 %i
+    simd_insert(v, i, j)
+}
+
+// CHECK-LABEL: @insert_s
+#[no_mangle]
+pub unsafe fn insert_s(v: S<4>, i: u32, j: f32) -> S<4>  {
+    // CHECK: insertelement <4 x float> %1, float %j, i32 %i
+    simd_insert(v, i, j)
+}
diff --git a/src/test/codegen/simd-intrinsic/simd-intrinsic-transmute-array.rs b/src/test/codegen/simd-intrinsic/simd-intrinsic-transmute-array.rs
new file mode 100644
index 00000000000..23098e7f649
--- /dev/null
+++ b/src/test/codegen/simd-intrinsic/simd-intrinsic-transmute-array.rs
@@ -0,0 +1,44 @@
+// ignore-tidy-linelength
+// compile-flags: -C no-prepopulate-passes
+// min-llvm-version 8.0
+
+#![crate_type = "lib"]
+
+#![allow(non_camel_case_types, incomplete_features)]
+#![feature(repr_simd, platform_intrinsics, const_generics)]
+
+#[repr(simd)]
+#[derive(Copy, Clone)]
+pub struct S<const N: usize>([f32; N]);
+
+#[repr(simd)]
+#[derive(Copy, Clone)]
+pub struct T([f32; 4]);
+
+#[repr(simd)]
+#[derive(Copy, Clone)]
+pub struct U(f32, f32, f32, f32);
+
+// CHECK-LABEL: @build_array_s
+#[no_mangle]
+pub fn build_array_s(x: [f32; 4]) -> S<4> {
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.*}} %{{[0-9]+}}, i8* {{.*}} %3, i64 16, i1 false)
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.*}} %{{[0-9]+}}, i8* {{.*}} %6, i64 16, i1 false)
+    S::<4>(x)
+}
+
+// CHECK-LABEL: @build_array_t
+#[no_mangle]
+pub fn build_array_t(x: [f32; 4]) -> T {
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.*}} %{{[0-9]+}}, i8* {{.*}} %3, i64 16, i1 false)
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.*}} %{{[0-9]+}}, i8* {{.*}} %6, i64 16, i1 false)
+    T(x)
+}
+
+// CHECK-LABEL: @build_array_u
+#[no_mangle]
+pub fn build_array_u(x: [f32; 4]) -> U {
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.*}} %{{[0-9]+}}, i8* {{.*}} %3, i64 16, i1 false)
+    // CHECK: call void @llvm.memcpy.p0i8.p0i8.i64(i8* {{.*}} %{{[0-9]+}}, i8* {{.*}} %6, i64 16, i1 false)
+    unsafe { std::mem::transmute(x) }
+}