Fix argument ABI for overaligned structs on ppc64le

When passing a 16 (or higher) aligned struct by value on ppc64le,
it needs to be passed as an array of `i128` rather than an array
of `i64`. This will force the use of an even starting register.

For the case of a 16 byte struct with alignment 16 it is important
that `[1 x i128]` is used instead of `i128` -- apparently, the
latter will get treated similarly to `[2 x i64]`, not exhibiting
the correct ABI. Add a `force_array` flag to `Uniform` to support
this.

The relevant clang code can be found here:
https://github.com/llvm/llvm-project/blob/fe2119a7b08b6e468b2a67768904ea85b1bf0a45/clang/lib/CodeGen/Targets/PPC.cpp#L878-L884
https://github.com/llvm/llvm-project/blob/fe2119a7b08b6e468b2a67768904ea85b1bf0a45/clang/lib/CodeGen/Targets/PPC.cpp#L780-L784

I think the corresponding psABI wording is this:

> Fixed size aggregates and unions passed by value are mapped to as
> many doublewords of the parameter save area as the value uses in
> memory. Aggregrates and unions are aligned according to their
> alignment requirements. This may result in doublewords being
> skipped for alignment.

In particular the last sentence.

Fixes https://github.com/rust-lang/rust/issues/122767.

1 files changed, 93 insertions, 0 deletions

diff --git a/tests/codegen/powerpc64le-struct-align-128.rs b/tests/codegen/powerpc64le-struct-align-128.rs
new file mode 100644
index 00000000000..0096c6d3138
--- /dev/null
+++ b/tests/codegen/powerpc64le-struct-align-128.rs
@@ -0,0 +1,93 @@
+// Test that structs aligned to 128 bits are passed with the correct ABI on powerpc64le.
+// This is similar to aarch64-struct-align-128.rs, but for ppc.
+
+//@ compile-flags: --target powerpc64le-unknown-linux-gnu
+//@ needs-llvm-components: powerpc
+
+#![feature(no_core, lang_items)]
+#![crate_type = "lib"]
+#![no_core]
+
+#[lang="sized"]
+trait Sized { }
+#[lang="freeze"]
+trait Freeze { }
+#[lang="copy"]
+trait Copy { }
+
+#[repr(C)]
+pub struct Align8 {
+    pub a: u64,
+    pub b: u64,
+}
+
+#[repr(transparent)]
+pub struct Transparent8 {
+    a: Align8
+}
+
+#[repr(C)]
+pub struct Wrapped8 {
+    a: Align8,
+}
+
+extern "C" {
+    // CHECK: declare void @test_8([2 x i64], [2 x i64], [2 x i64])
+    fn test_8(a: Align8, b: Transparent8, c: Wrapped8);
+}
+
+#[repr(C)]
+#[repr(align(16))]
+pub struct Align16 {
+    pub a: u64,
+    pub b: u64,
+}
+
+#[repr(transparent)]
+pub struct Transparent16 {
+    a: Align16
+}
+
+#[repr(C)]
+pub struct Wrapped16 {
+    pub a: Align16,
+}
+
+extern "C" {
+    // It's important that this produces [1 x i128]  rather than just i128!
+    // CHECK: declare void @test_16([1 x i128], [1 x i128], [1 x i128])
+    fn test_16(a: Align16, b: Transparent16, c: Wrapped16);
+}
+
+#[repr(C)]
+#[repr(align(32))]
+pub struct Align32 {
+    pub a: u64,
+    pub b: u64,
+    pub c: u64,
+}
+
+#[repr(transparent)]
+pub struct Transparent32 {
+    a: Align32
+}
+
+#[repr(C)]
+pub struct Wrapped32 {
+    pub a: Align32,
+}
+
+extern "C" {
+    // CHECK: declare void @test_32([2 x i128], [2 x i128], [2 x i128])
+    fn test_32(a: Align32, b: Transparent32, c: Wrapped32);
+}
+
+pub unsafe fn main(
+    a1: Align8, a2: Transparent8, a3: Wrapped8,
+    b1: Align16, b2: Transparent16, b3: Wrapped16,
+    c1: Align32, c2: Transparent32, c3: Wrapped32,
+) {
+    test_8(a1, a2, a3);
+    test_16(b1, b2, b3);
+    test_32(c1, c2, c3);
+}