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:
fe2119a7b0/clang/lib/CodeGen/Targets/PPC.cpp (L878-L884)
fe2119a7b0/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.

compiler/rustc_codegen_llvm/src/abi.rs

@@ -150,7 +150,7 @@ impl LlvmType for CastTarget {
         // Simplify to a single unit or an array if there's no prefix.
         // This produces the same layout, but using a simpler type.
         if self.prefix.iter().all(|x| x.is_none()) {
-            if rest_count == 1 {
+            if rest_count == 1 && !self.rest.force_array {
                 return rest_ll_unit;
             }
 

compiler/rustc_target/src/abi/call/aarch64.rs

@@ -31,7 +31,7 @@ where
             RegKind::Vector => size.bits() == 64 || size.bits() == 128,
         };
 
-        valid_unit.then_some(Uniform { unit, total: size })
+        valid_unit.then_some(Uniform { unit, total: size, force_array: false })
     })
 }
 
@@ -60,7 +60,7 @@ where
     let size = ret.layout.size;
     let bits = size.bits();
     if bits <= 128 {
-        ret.cast_to(Uniform { unit: Reg::i64(), total: size });
+        ret.cast_to(Uniform { unit: Reg::i64(), total: size, force_array: false });
         return;
     }
     ret.make_indirect();
@@ -100,9 +100,9 @@ where
     };
     if size.bits() <= 128 {
         if align.bits() == 128 {
-            arg.cast_to(Uniform { unit: Reg::i128(), total: size });
+            arg.cast_to(Uniform { unit: Reg::i128(), total: size, force_array: false });
         } else {
-            arg.cast_to(Uniform { unit: Reg::i64(), total: size });
+            arg.cast_to(Uniform { unit: Reg::i64(), total: size, force_array: false });
         }
         return;
     }

compiler/rustc_target/src/abi/call/arm.rs

@@ -21,7 +21,7 @@ where
             RegKind::Vector => size.bits() == 64 || size.bits() == 128,
         };
 
-        valid_unit.then_some(Uniform { unit, total: size })
+        valid_unit.then_some(Uniform { unit, total: size, force_array: false })
     })
 }
 
@@ -49,7 +49,7 @@ where
     let size = ret.layout.size;
     let bits = size.bits();
     if bits <= 32 {
-        ret.cast_to(Uniform { unit: Reg::i32(), total: size });
+        ret.cast_to(Uniform { unit: Reg::i32(), total: size, force_array: false });
         return;
     }
     ret.make_indirect();
@@ -78,7 +78,11 @@ where
 
     let align = arg.layout.align.abi.bytes();
     let total = arg.layout.size;
-    arg.cast_to(Uniform { unit: if align <= 4 { Reg::i32() } else { Reg::i64() }, total });
+    arg.cast_to(Uniform {
+        unit: if align <= 4 { Reg::i32() } else { Reg::i64() },
+        total,
+        force_array: false,
+    });
 }
 
 pub fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)

compiler/rustc_target/src/abi/call/csky.rs

@@ -18,7 +18,7 @@ fn classify_ret<Ty>(arg: &mut ArgAbi<'_, Ty>) {
         if total.bits() > 64 {
             arg.make_indirect();
         } else if total.bits() > 32 {
-            arg.cast_to(Uniform { unit: Reg::i32(), total });
+            arg.cast_to(Uniform { unit: Reg::i32(), total, force_array: false });
         } else {
             arg.cast_to(Reg::i32());
         }
@@ -38,7 +38,7 @@ fn classify_arg<Ty>(arg: &mut ArgAbi<'_, Ty>) {
     if arg.layout.is_aggregate() {
         let total = arg.layout.size;
         if total.bits() > 32 {
-            arg.cast_to(Uniform { unit: Reg::i32(), total });
+            arg.cast_to(Uniform { unit: Reg::i32(), total, force_array: false });
         } else {
             arg.cast_to(Reg::i32());
         }

compiler/rustc_target/src/abi/call/loongarch.rs

@@ -195,7 +195,11 @@ where
         if total.bits() <= xlen {
             arg.cast_to(xlen_reg);
         } else {
-            arg.cast_to(Uniform { unit: xlen_reg, total: Size::from_bits(xlen * 2) });
+            arg.cast_to(Uniform {
+                unit: xlen_reg,
+                total: Size::from_bits(xlen * 2),
+                force_array: false,
+            });
         }
         return false;
     }
@@ -281,6 +285,7 @@ fn classify_arg<'a, Ty, C>(
             arg.cast_to(Uniform {
                 unit: if align_regs { double_xlen_reg } else { xlen_reg },
                 total: Size::from_bits(xlen * 2),
+                force_array: false,
             });
         }
         if align_regs && is_vararg {

compiler/rustc_target/src/abi/call/mips.rs

@@ -27,7 +27,10 @@ where
 
     if arg.layout.is_aggregate() {
         let pad_i32 = !offset.is_aligned(align);
-        arg.cast_to_and_pad_i32(Uniform { unit: Reg::i32(), total: size }, pad_i32);
+        arg.cast_to_and_pad_i32(
+            Uniform { unit: Reg::i32(), total: size, force_array: false },
+            pad_i32,
+        );
     } else {
         arg.extend_integer_width_to(32);
     }

compiler/rustc_target/src/abi/call/mips64.rs

@@ -68,7 +68,7 @@ where
         }
 
         // Cast to a uniform int structure
-        ret.cast_to(Uniform { unit: Reg::i64(), total: size });
+        ret.cast_to(Uniform { unit: Reg::i64(), total: size, force_array: false });
     } else {
         ret.make_indirect();
     }
@@ -139,7 +139,7 @@ where
     let rest_size = size - Size::from_bytes(8) * prefix_index as u64;
     arg.cast_to(CastTarget {
         prefix,
-        rest: Uniform { unit: Reg::i64(), total: rest_size },
+        rest: Uniform { unit: Reg::i64(), total: rest_size, force_array: false },
         attrs: ArgAttributes {
             regular: ArgAttribute::default(),
             arg_ext: ArgExtension::None,

compiler/rustc_target/src/abi/call/mod.rs

@@ -255,11 +255,14 @@ pub struct Uniform {
     ///   for 64-bit integers with a total size of 20 bytes. When the argument is actually passed,
     ///   this size will be rounded up to the nearest multiple of `unit.size`.
     pub total: Size,
+
+    /// Force the use of an array, even if there is only a single element.
+    pub force_array: bool,
 }
 
 impl From<Reg> for Uniform {
     fn from(unit: Reg) -> Uniform {
-        Uniform { unit, total: unit.size }
+        Uniform { unit, total: unit.size, force_array: false }
     }
 }
 

compiler/rustc_target/src/abi/call/nvptx64.rs

@@ -35,7 +35,7 @@ where
             16 => Reg::i128(),
             _ => unreachable!("Align is given as power of 2 no larger than 16 bytes"),
         };
-        arg.cast_to(Uniform { unit, total: Size::from_bytes(2 * align_bytes) });
+        arg.cast_to(Uniform { unit, total: Size::from_bytes(2 * align_bytes), force_array: false });
     } else {
         // FIXME: find a better way to do this. See https://github.com/rust-lang/rust/issues/117271.
         arg.make_direct_deprecated();

compiler/rustc_target/src/abi/call/powerpc64.rs

@@ -2,7 +2,7 @@
 // Alignment of 128 bit types is not currently handled, this will
 // need to be fixed when PowerPC vector support is added.
 
-use crate::abi::call::{ArgAbi, FnAbi, Reg, RegKind, Uniform};
+use crate::abi::call::{Align, ArgAbi, FnAbi, Reg, RegKind, Uniform};
 use crate::abi::{Endian, HasDataLayout, TyAbiInterface};
 use crate::spec::HasTargetSpec;
 
@@ -37,7 +37,7 @@ where
             RegKind::Vector => arg.layout.size.bits() == 128,
         };
 
-        valid_unit.then_some(Uniform { unit, total: arg.layout.size })
+        valid_unit.then_some(Uniform { unit, total: arg.layout.size, force_array: false })
     })
 }
 
@@ -81,7 +81,7 @@ where
             Reg::i64()
         };
 
-        ret.cast_to(Uniform { unit, total: size });
+        ret.cast_to(Uniform { unit, total: size, force_array: false });
         return;
     }
 
@@ -108,18 +108,21 @@ where
     }
 
     let size = arg.layout.size;
-    let (unit, total) = if size.bits() <= 64 {
+    if size.bits() <= 64 {
         // Aggregates smaller than a doubleword should appear in
         // the least-significant bits of the parameter doubleword.
-        (Reg { kind: RegKind::Integer, size }, size)
+        arg.cast_to(Reg { kind: RegKind::Integer, size })
     } else {
-        // Aggregates larger than a doubleword should be padded
-        // at the tail to fill out a whole number of doublewords.
-        let reg_i64 = Reg::i64();
-        (reg_i64, size.align_to(reg_i64.align(cx)))
+        // Aggregates larger than i64 should be padded at the tail to fill out a whole number
+        // of i64s or i128s, depending on the aggregate alignment. Always use an array for
+        // this, even if there is only a single element.
+        let reg = if arg.layout.align.abi.bytes() > 8 { Reg::i128() } else { Reg::i64() };
+        arg.cast_to(Uniform {
+            unit: reg,
+            total: size.align_to(Align::from_bytes(reg.size.bytes()).unwrap()),
+            force_array: true,
+        })
     };
-
-    arg.cast_to(Uniform { unit, total });
 }
 
 pub fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)

compiler/rustc_target/src/abi/call/riscv.rs

@@ -201,7 +201,11 @@ where
         if total.bits() <= xlen {
             arg.cast_to(xlen_reg);
         } else {
-            arg.cast_to(Uniform { unit: xlen_reg, total: Size::from_bits(xlen * 2) });
+            arg.cast_to(Uniform {
+                unit: xlen_reg,
+                total: Size::from_bits(xlen * 2),
+                force_array: false,
+            });
         }
         return false;
     }
@@ -287,6 +291,7 @@ fn classify_arg<'a, Ty, C>(
             arg.cast_to(Uniform {
                 unit: if align_regs { double_xlen_reg } else { xlen_reg },
                 total: Size::from_bits(xlen * 2),
+                force_array: false,
             });
         }
         if align_regs && is_vararg {

compiler/rustc_target/src/abi/call/sparc.rs

@@ -27,7 +27,10 @@ where
 
     if arg.layout.is_aggregate() {
         let pad_i32 = !offset.is_aligned(align);
-        arg.cast_to_and_pad_i32(Uniform { unit: Reg::i32(), total: size }, pad_i32);
+        arg.cast_to_and_pad_i32(
+            Uniform { unit: Reg::i32(), total: size, force_array: false },
+            pad_i32,
+        );
     } else {
         arg.extend_integer_width_to(32);
     }

compiler/rustc_target/src/abi/call/sparc64.rs

@@ -192,7 +192,7 @@ where
 
                 arg.cast_to(CastTarget {
                     prefix: data.prefix,
-                    rest: Uniform { unit: Reg::i64(), total: rest_size },
+                    rest: Uniform { unit: Reg::i64(), total: rest_size, force_array: false },
                     attrs: ArgAttributes {
                         regular: data.arg_attribute,
                         arg_ext: ArgExtension::None,
@@ -205,7 +205,7 @@ where
         }
     }
 
-    arg.cast_to(Uniform { unit: Reg::i64(), total });
+    arg.cast_to(Uniform { unit: Reg::i64(), total, force_array: false });
 }
 
 pub fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'a, Ty>)

compiler/rustc_target/src/abi/call/wasm.rs

@@ -1,4 +1,4 @@
-use crate::abi::call::{ArgAbi, FnAbi, Uniform};
+use crate::abi::call::{ArgAbi, FnAbi};
 use crate::abi::{HasDataLayout, TyAbiInterface};
 
 fn unwrap_trivial_aggregate<'a, Ty, C>(cx: &C, val: &mut ArgAbi<'a, Ty>) -> bool
@@ -10,7 +10,7 @@ where
         if let Some(unit) = val.layout.homogeneous_aggregate(cx).ok().and_then(|ha| ha.unit()) {
             let size = val.layout.size;
             if unit.size == size {
-                val.cast_to(Uniform { unit, total: size });
+                val.cast_to(unit);
                 return true;
             }
         }

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);
+}