Auto merge of #116672 - maurer:128-align, r=nikic

LLVM 18 x86 data layout update

With https://reviews.llvm.org/D86310 LLVM now has i128 aligned to 16-bytes on x86 based platforms. This will be in LLVM-18. This patch updates all our spec targets to be 16-byte aligned, and removes the alignment when speaking to older LLVM.

This results in Rust overaligning things relative to LLVM on older LLVMs.

This implements MCP https://github.com/rust-lang/compiler-team/issues/683.

See #54341

1 files changed, 103 insertions, 0 deletions

diff --git a/tests/codegen/i128-x86-align.rs b/tests/codegen/i128-x86-align.rs
new file mode 100644
index 00000000000..aaf5785dc9f
--- /dev/null
+++ b/tests/codegen/i128-x86-align.rs
@@ -0,0 +1,103 @@
+// only-x86_64
+// compile-flags: -O -C no-prepopulate-passes --crate-type=lib
+
+// On LLVM 17 and earlier LLVM's own data layout specifies that i128 has 8 byte alignment,
+// while rustc wants it to have 16 byte alignment. This test checks that we handle this
+// correctly.
+
+// CHECK: %ScalarPair = type { i32, [3 x i32], i128 }
+// CHECK: %Struct = type { i32, i32, [2 x i32], i128 }
+
+#![feature(core_intrinsics)]
+
+#[repr(C)]
+#[derive(Clone, Copy)]
+pub struct ScalarPair {
+    a: i32,
+    b: i128,
+}
+
+#[no_mangle]
+pub fn load(x: &ScalarPair) -> ScalarPair {
+    // CHECK-LABEL: @load(
+    // CHECK-SAME: align 16 dereferenceable(32) %x
+    // CHECK:      [[A:%.*]] = load i32, ptr %x, align 16
+    // CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i8, ptr %x, i64 16
+    // CHECK-NEXT: [[B:%.*]] = load i128, ptr [[GEP]], align 16
+    // CHECK-NEXT: [[IV1:%.*]] = insertvalue { i32, i128 } poison, i32 [[A]], 0
+    // CHECK-NEXT: [[IV2:%.*]] = insertvalue { i32, i128 } [[IV1]], i128 [[B]], 1
+    // CHECK-NEXT: ret { i32, i128 } [[IV2]]
+    *x
+}
+
+#[no_mangle]
+pub fn store(x: &mut ScalarPair) {
+    // CHECK-LABEL: @store(
+    // CHECK-SAME: align 16 dereferenceable(32) %x
+    // CHECK:      store i32 1, ptr %x, align 16
+    // CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i8, ptr %x, i64 16
+    // CHECK-NEXT: store i128 2, ptr [[GEP]], align 16
+    *x = ScalarPair { a: 1, b: 2 };
+}
+
+#[no_mangle]
+pub fn alloca() {
+    // CHECK-LABEL: @alloca(
+    // CHECK:      [[X:%.*]] = alloca %ScalarPair, align 16
+    // CHECK:      store i32 1, ptr %x, align 16
+    // CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i8, ptr %x, i64 16
+    // CHECK-NEXT: store i128 2, ptr [[GEP]], align 16
+    let mut x = ScalarPair { a: 1, b: 2 };
+    store(&mut x);
+}
+
+#[no_mangle]
+pub fn load_volatile(x: &ScalarPair) -> ScalarPair {
+    // CHECK-LABEL: @load_volatile(
+    // CHECK-SAME: align 16 dereferenceable(32) %x
+    // CHECK:      [[TMP:%.*]] = alloca %ScalarPair, align 16
+    // CHECK:      [[LOAD:%.*]] = load volatile %ScalarPair, ptr %x, align 16
+    // CHECK-NEXT: store %ScalarPair [[LOAD]], ptr [[TMP]], align 16
+    // CHECK-NEXT: [[A:%.*]] = load i32, ptr [[TMP]], align 16
+    // CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i8, ptr [[TMP]], i64 16
+    // CHECK-NEXT: [[B:%.*]] = load i128, ptr [[GEP]], align 16
+    unsafe { std::intrinsics::volatile_load(x) }
+}
+
+#[no_mangle]
+pub fn transmute(x: ScalarPair) -> (std::mem::MaybeUninit<i128>, i128) {
+    // CHECK-LABEL: define { i128, i128 } @transmute(i32 noundef %x.0, i128 noundef %x.1)
+    // CHECK:       [[TMP:%.*]] = alloca { i128, i128 }, align 16
+    // CHECK-NEXT:  store i32 %x.0, ptr [[TMP]], align 16
+    // CHECK-NEXT:  [[GEP:%.*]] = getelementptr inbounds i8, ptr [[TMP]], i64 16
+    // CHECK-NEXT:  store i128 %x.1, ptr [[GEP]], align 16
+    // CHECK-NEXT:  [[LOAD1:%.*]] = load i128, ptr %_0, align 16
+    // CHECK-NEXT:  [[GEP2:%.*]] = getelementptr inbounds i8, ptr [[TMP]], i64 16
+    // CHECK-NEXT:  [[LOAD2:%.*]] = load i128, ptr [[GEP2]], align 16
+    // CHECK-NEXT:  [[IV1:%.*]] = insertvalue { i128, i128 } poison, i128 [[LOAD1]], 0
+    // CHECK-NEXT:  [[IV2:%.*]] = insertvalue { i128, i128 } [[IV1]], i128 [[LOAD2]], 1
+    // CHECK-NEXT:  ret { i128, i128 } [[IV2]]
+    unsafe { std::mem::transmute(x) }
+}
+
+#[repr(C)]
+#[derive(Clone, Copy)]
+pub struct Struct {
+    a: i32,
+    b: i32,
+    c: i128,
+}
+
+#[no_mangle]
+pub fn store_struct(x: &mut Struct) {
+    // CHECK-LABEL: @store_struct(
+    // CHECK-SAME: align 16 dereferenceable(32) %x
+    // CHECK:      [[TMP:%.*]] = alloca %Struct, align 16
+    // CHECK:      store i32 1, ptr [[TMP]], align 16
+    // CHECK-NEXT: [[GEP1:%.*]] = getelementptr inbounds %Struct, ptr [[TMP]], i32 0, i32 1
+    // CHECK-NEXT: store i32 2, ptr [[GEP1]], align 4
+    // CHECK-NEXT: [[GEP2:%.*]] = getelementptr inbounds %Struct, ptr [[TMP]], i32 0, i32 3
+    // CHECK-NEXT: store i128 3, ptr [[GEP2]], align 16
+    // CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 16 %x, ptr align 16 [[TMP]], i64 32, i1 false)
+    *x = Struct { a: 1, b: 2, c: 3 };
+}