implement va_arg for powerpc

This actually fixes a bug where before only 20 arguments could be passed. As far as I can tell, an arbitrary number of arguments is now supported

compiler/rustc_codegen_llvm/src/va_arg.rs

@@ -237,6 +237,150 @@ fn emit_aapcs_va_arg<'ll, 'tcx>(
     val
 }
 
+fn emit_powerpc_va_arg<'ll, 'tcx>(
+    bx: &mut Builder<'_, 'll, 'tcx>,
+    list: OperandRef<'tcx, &'ll Value>,
+    target_ty: Ty<'tcx>,
+) -> &'ll Value {
+    let dl = bx.cx.data_layout();
+
+    // struct __va_list_tag {
+    //   unsigned char gpr;
+    //   unsigned char fpr;
+    //   unsigned short reserved;
+    //   void *overflow_arg_area;
+    //   void *reg_save_area;
+    // };
+    let va_list_addr = list.immediate();
+
+    // Peel off any newtype wrappers.
+    let layout = {
+        let mut layout = bx.cx.layout_of(target_ty);
+
+        while let Some((_, inner)) = layout.non_1zst_field(bx.cx) {
+            layout = inner;
+        }
+
+        layout
+    };
+
+    // Rust does not currently support any powerpc softfloat targets.
+    let target = &bx.cx.tcx.sess.target;
+    let is_soft_float_abi = target.abi == "softfloat";
+    assert!(!is_soft_float_abi);
+
+    // All instances of VaArgSafe are passed directly.
+    let is_indirect = false;
+
+    let (is_i64, is_int, is_f64) = match layout.layout.backend_repr() {
+        BackendRepr::Scalar(scalar) => match scalar.primitive() {
+            rustc_abi::Primitive::Int(integer, _) => (integer.size().bits() == 64, true, false),
+            rustc_abi::Primitive::Float(float) => (false, false, float.size().bits() == 64),
+            rustc_abi::Primitive::Pointer(_) => (false, true, false),
+        },
+        _ => unreachable!("all instances of VaArgSafe are represented as scalars"),
+    };
+
+    let num_regs_addr = if is_int || is_soft_float_abi {
+        va_list_addr // gpr
+    } else {
+        bx.inbounds_ptradd(va_list_addr, bx.const_usize(1)) // fpr
+    };
+
+    let mut num_regs = bx.load(bx.type_i8(), num_regs_addr, dl.i8_align.abi);
+
+    // "Align" the register count when the type is passed as `i64`.
+    if is_i64 || (is_f64 && is_soft_float_abi) {
+        num_regs = bx.add(num_regs, bx.const_u8(1));
+        num_regs = bx.and(num_regs, bx.const_u8(0b1111_1110));
+    }
+
+    let max_regs = 8u8;
+    let use_regs = bx.icmp(IntPredicate::IntULT, num_regs, bx.const_u8(max_regs));
+
+    let in_reg = bx.append_sibling_block("va_arg.in_reg");
+    let in_mem = bx.append_sibling_block("va_arg.in_mem");
+    let end = bx.append_sibling_block("va_arg.end");
+
+    bx.cond_br(use_regs, in_reg, in_mem);
+
+    let reg_addr = {
+        bx.switch_to_block(in_reg);
+
+        let reg_safe_area_ptr = bx.inbounds_ptradd(va_list_addr, bx.cx.const_usize(1 + 1 + 2 + 4));
+        let mut reg_addr = bx.load(bx.type_ptr(), reg_safe_area_ptr, dl.pointer_align.abi);
+
+        // Floating-point registers start after the general-purpose registers.
+        if !is_int && !is_soft_float_abi {
+            reg_addr = bx.inbounds_ptradd(reg_addr, bx.cx.const_usize(32))
+        }
+
+        // Get the address of the saved value by scaling the number of
+        // registers we've used by the number of.
+        let reg_size = if is_int || is_soft_float_abi { 4 } else { 8 };
+        let reg_offset = bx.mul(num_regs, bx.cx().const_u8(reg_size));
+        let reg_addr = bx.inbounds_ptradd(reg_addr, reg_offset);
+
+        // Increase the used-register count.
+        let reg_incr = if is_i64 || (is_f64 && is_soft_float_abi) { 2 } else { 1 };
+        let new_num_regs = bx.add(num_regs, bx.cx.const_u8(reg_incr));
+        bx.store(new_num_regs, num_regs_addr, dl.i8_align.abi);
+
+        bx.br(end);
+
+        reg_addr
+    };
+
+    let mem_addr = {
+        bx.switch_to_block(in_mem);
+
+        bx.store(bx.const_u8(max_regs), num_regs_addr, dl.i8_align.abi);
+
+        // Everything in the overflow area is rounded up to a size of at least 4.
+        let overflow_area_align = Align::from_bytes(4).unwrap();
+
+        let size = if !is_indirect {
+            layout.layout.size.align_to(overflow_area_align)
+        } else {
+            dl.pointer_size
+        };
+
+        let overflow_area_ptr = bx.inbounds_ptradd(va_list_addr, bx.cx.const_usize(1 + 1 + 2));
+        let mut overflow_area = bx.load(bx.type_ptr(), overflow_area_ptr, dl.pointer_align.abi);
+
+        // Round up address of argument to alignment
+        if layout.layout.align.abi > overflow_area_align {
+            overflow_area = round_pointer_up_to_alignment(
+                bx,
+                overflow_area,
+                layout.layout.align.abi,
+                bx.type_ptr(),
+            );
+        }
+
+        let mem_addr = overflow_area;
+
+        // Increase the overflow area.
+        overflow_area = bx.inbounds_ptradd(overflow_area, bx.const_usize(size.bytes()));
+        bx.store(overflow_area, overflow_area_ptr, dl.pointer_align.abi);
+
+        bx.br(end);
+
+        mem_addr
+    };
+
+    // Return the appropriate result.
+    bx.switch_to_block(end);
+    let val_addr = bx.phi(bx.type_ptr(), &[reg_addr, mem_addr], &[in_reg, in_mem]);
+    let val_type = layout.llvm_type(bx);
+    let val_addr = if is_indirect {
+        bx.load(bx.cx.type_ptr(), val_addr, dl.pointer_align.abi)
+    } else {
+        val_addr
+    };
+    bx.load(val_type, val_addr, layout.align.abi)
+}
+
 fn emit_s390x_va_arg<'ll, 'tcx>(
     bx: &mut Builder<'_, 'll, 'tcx>,
     list: OperandRef<'tcx, &'ll Value>,
@@ -740,17 +884,6 @@ pub(super) fn emit_va_arg<'ll, 'tcx>(
     let target = &bx.cx.tcx.sess.target;
 
     match &*target.arch {
-        // Windows x86
-        "x86" if target.is_like_windows => emit_ptr_va_arg(
-            bx,
-            addr,
-            target_ty,
-            PassMode::Direct,
-            SlotSize::Bytes4,
-            AllowHigherAlign::No,
-            ForceRightAdjust::No,
-        ),
-        // Generic x86
         "x86" => emit_ptr_va_arg(
             bx,
             addr,
@@ -773,6 +906,7 @@ pub(super) fn emit_va_arg<'ll, 'tcx>(
         }
         "aarch64" => emit_aapcs_va_arg(bx, addr, target_ty),
         "s390x" => emit_s390x_va_arg(bx, addr, target_ty),
+        "powerpc" => emit_powerpc_va_arg(bx, addr, target_ty),
         "powerpc64" | "powerpc64le" => emit_ptr_va_arg(
             bx,
             addr,