Fix C aggregate-passing ABI on powerpc

The existing code (which looks like it was copied from MIPS) passes
aggregates by value in registers. This is wrong. According to the SVR4
powerpc psABI, all aggregates are passed indirectly.

See #64259 for more discussion, which addresses the ABI for the special
case of ZSTs (empty structs).

src/librustc_target/abi/call/mod.rs

@@ -554,7 +554,7 @@ impl<'a, Ty> FnAbi<'a, Ty> {
             "arm" => arm::compute_abi_info(cx, self),
             "mips" => mips::compute_abi_info(cx, self),
             "mips64" => mips64::compute_abi_info(cx, self),
-            "powerpc" => powerpc::compute_abi_info(cx, self),
+            "powerpc" => powerpc::compute_abi_info(self),
             "powerpc64" => powerpc64::compute_abi_info(cx, self),
             "s390x" => s390x::compute_abi_info(cx, self),
             "msp430" => msp430::compute_abi_info(self),

src/librustc_target/abi/call/powerpc.rs

@@ -1,49 +1,28 @@
-use crate::abi::call::{ArgAbi, FnAbi, Reg, Uniform};
-use crate::abi::{HasDataLayout, LayoutOf, Size, TyLayoutMethods};
+use crate::abi::call::{ArgAbi, FnAbi};
 
-fn classify_ret<'a, Ty, C>(cx: &C, ret: &mut ArgAbi<'_, Ty>, offset: &mut Size)
-    where Ty: TyLayoutMethods<'a, C>, C: LayoutOf<Ty = Ty> + HasDataLayout
-{
-    if !ret.layout.is_aggregate() {
-        ret.extend_integer_width_to(32);
-    } else {
+fn classify_ret<Ty>(ret: &mut ArgAbi<'_, Ty>) {
+    if ret.layout.is_aggregate() {
         ret.make_indirect();
-        *offset += cx.data_layout().pointer_size;
+    } else {
+        ret.extend_integer_width_to(32);
     }
 }
 
-fn classify_arg<'a, Ty, C>(cx: &C, arg: &mut ArgAbi<'_, Ty>, offset: &mut Size)
-    where Ty: TyLayoutMethods<'a, C>, C: LayoutOf<Ty = Ty> + HasDataLayout
-{
-    let dl = cx.data_layout();
-    let size = arg.layout.size;
-    let align = arg.layout.align.max(dl.i32_align).min(dl.i64_align).abi;
-
+fn classify_arg<Ty>(arg: &mut ArgAbi<'_, Ty>) {
     if arg.layout.is_aggregate() {
-        arg.cast_to(Uniform {
-            unit: Reg::i32(),
-            total: size
-        });
-        if !offset.is_aligned(align) {
-            arg.pad_with(Reg::i32());
-        }
+        arg.make_indirect();
     } else {
         arg.extend_integer_width_to(32);
     }
-
-    *offset = offset.align_to(align) + size.align_to(align);
 }
 
-pub fn compute_abi_info<'a, Ty, C>(cx: &C, fn_abi: &mut FnAbi<'_, Ty>)
-    where Ty: TyLayoutMethods<'a, C>, C: LayoutOf<Ty = Ty> + HasDataLayout
-{
-    let mut offset = Size::ZERO;
+pub fn compute_abi_info<Ty>(fn_abi: &mut FnAbi<'_, Ty>) {
     if !fn_abi.ret.is_ignore() {
-        classify_ret(cx, &mut fn_abi.ret, &mut offset);
+        classify_ret(&mut fn_abi.ret);
     }
 
     for arg in &mut fn_abi.args {
         if arg.is_ignore() { continue; }
-        classify_arg(cx, arg, &mut offset);
+        classify_arg(arg);
     }
 }