Rollup merge of #145709 - heiher:issue-145692-1, r=jackh726

Fix LoongArch C function ABI when passing/returning structs containing floats

Similar to RISC-V, LoongArch passes structs containing only one or two floats (or a float–integer pair) in registers, as long as each element fits into a single corresponding register. Before this PR, Rust did not check the actual offset of the second float or integer; instead, it assumed the standard offset based on the default alignment. However, since the offset can be affected by `#[repr(align(N))]` and `#[repr(packed)]`, this led to miscompilations (see rust-lang/rust#145692). This PR fixes the issue by explicitly specifying the offset for the remainder of the cast.

1 files changed, 134 insertions, 0 deletions

diff --git a/tests/assembly-llvm/loongarch-float-struct-abi.rs b/tests/assembly-llvm/loongarch-float-struct-abi.rs
new file mode 100644
index 00000000000..4991004fc05
--- /dev/null
+++ b/tests/assembly-llvm/loongarch-float-struct-abi.rs
@@ -0,0 +1,134 @@
+//@ add-core-stubs
+//@ assembly-output: emit-asm
+//@ compile-flags: -Copt-level=3 --target loongarch64-unknown-linux-gnu
+//@ needs-llvm-components: loongarch
+
+#![feature(no_core, lang_items)]
+#![no_std]
+#![no_core]
+#![crate_type = "lib"]
+
+extern crate minicore;
+use minicore::*;
+
+#[repr(C, align(64))]
+struct Aligned(f64);
+
+#[repr(C)]
+struct Padded(u8, Aligned);
+
+#[repr(C, packed)]
+struct Packed(u8, f32);
+
+impl Copy for Aligned {}
+impl Copy for Padded {}
+impl Copy for Packed {}
+
+extern "C" {
+    fn take_padded(x: Padded);
+    fn get_padded() -> Padded;
+    fn take_packed(x: Packed);
+    fn get_packed() -> Packed;
+}
+
+// CHECK-LABEL: pass_padded
+#[unsafe(no_mangle)]
+extern "C" fn pass_padded(out: &mut Padded, x: Padded) {
+    // CHECK: st.b $a1, $a0, 0
+    // CHECK-NEXT: fst.d $fa0, $a0, 64
+    // CHECK-NEXT: ret
+    *out = x;
+}
+
+// CHECK-LABEL: ret_padded
+#[unsafe(no_mangle)]
+extern "C" fn ret_padded(x: &Padded) -> Padded {
+    // CHECK: fld.d $fa0, $a0, 64
+    // CHECK-NEXT: ld.b $a0, $a0, 0
+    // CHECK-NEXT: ret
+    *x
+}
+
+#[unsafe(no_mangle)]
+extern "C" fn call_padded(x: &Padded) {
+    // CHECK: fld.d $fa0, $a0, 64
+    // CHECK-NEXT: ld.b $a0, $a0, 0
+    // CHECK-NEXT: pcaddu18i $t8, %call36(take_padded)
+    // CHECK-NEXT: jr $t8
+    unsafe {
+        take_padded(*x);
+    }
+}
+
+#[unsafe(no_mangle)]
+extern "C" fn receive_padded(out: &mut Padded) {
+    // CHECK: addi.d $sp, $sp, -16
+    // CHECK-NEXT: .cfi_def_cfa_offset 16
+    // CHECK-NEXT: st.d $ra, $sp, [[#%d,RA_SPILL:]]
+    // CHECK-NEXT: st.d [[TEMP:.*]], $sp, [[#%d,TEMP_SPILL:]]
+    // CHECK-NEXT: .cfi_offset 1, [[#%d,RA_SPILL - 16]]
+    // CHECK-NEXT: .cfi_offset [[#%d,TEMP_NUM:]], [[#%d,TEMP_SPILL - 16]]
+    // CHECK-NEXT: move [[TEMP]], $a0
+    // CHECK-NEXT: pcaddu18i $ra, %call36(get_padded)
+    // CHECK-NEXT: jirl $ra, $ra, 0
+    // CHECK-NEXT: st.b $a0, [[TEMP]], 0
+    // CHECK-NEXT: fst.d $fa0, [[TEMP]], 64
+    // CHECK-NEXT: ld.d [[TEMP]], $sp, [[#%d,TEMP_SPILL]]
+    // CHECK-NEXT: ld.d $ra, $sp, [[#%d,RA_SPILL]]
+    // CHECK: addi.d $sp, $sp, 16
+    // CHECK: ret
+    unsafe {
+        *out = get_padded();
+    }
+}
+
+// CHECK-LABEL: pass_packed
+#[unsafe(no_mangle)]
+extern "C" fn pass_packed(out: &mut Packed, x: Packed) {
+    // CHECK: st.b $a1, $a0, 0
+    // CHECK-NEXT: fst.s $fa0, $a0, 1
+    // CHECK-NEXT: ret
+    *out = x;
+}
+
+// CHECK-LABEL: ret_packed
+#[unsafe(no_mangle)]
+extern "C" fn ret_packed(x: &Packed) -> Packed {
+    // CHECK: fld.s $fa0, $a0, 1
+    // CHECK-NEXT: ld.b $a0, $a0, 0
+    // CHECK-NEXT: ret
+    *x
+}
+
+#[unsafe(no_mangle)]
+extern "C" fn call_packed(x: &Packed) {
+    // CHECK: fld.s $fa0, $a0, 1
+    // CHECK-NEXT: ld.b $a0, $a0, 0
+    // CHECK-NEXT: pcaddu18i $t8, %call36(take_packed)
+    // CHECK-NEXT: jr $t8
+    unsafe {
+        take_packed(*x);
+    }
+}
+
+#[unsafe(no_mangle)]
+extern "C" fn receive_packed(out: &mut Packed) {
+    // CHECK: addi.d $sp, $sp, -16
+    // CHECK-NEXT: .cfi_def_cfa_offset 16
+    // CHECK-NEXT: st.d $ra, $sp, [[#%d,RA_SPILL:]]
+    // CHECK-NEXT: st.d [[TEMP:.*]], $sp, [[#%d,TEMP_SPILL:]]
+    // CHECK-NEXT: .cfi_offset 1, [[#%d,RA_SPILL - 16]]
+    // CHECK-NEXT: .cfi_offset [[#%d,TEMP_NUM:]], [[#%d,TEMP_SPILL - 16]]
+    // CHECK-NEXT: move [[TEMP]], $a0
+    // CHECK-NEXT: pcaddu18i $ra, %call36(get_packed)
+    // CHECK-NEXT: jirl $ra, $ra, 0
+    // CHECK-NEXT: st.b $a0, [[TEMP]], 0
+    // CHECK-NEXT: fst.s $fa0, [[TEMP]], 1
+    // CHECK-NEXT: ld.d [[TEMP]], $sp, [[#%d,TEMP_SPILL]]
+    // CHECK-NEXT: ld.d $ra, $sp, [[#%d,RA_SPILL]]
+    // CHECK: addi.d $sp, $sp, 16
+    // CHECK: ret
+    unsafe {
+        *out = get_packed();
+    }
+}