From 3e30ba3f20dce2d406253de3fc0eb86934a3eaa7 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Tue, 7 Jun 2022 20:51:14 -0700
Subject: stage2: better codegen for byte-aligned packed struct fields

 * Sema: handle overaligned packed struct field pointers
 * LLVM: handle byte-aligned packed struct field pointers
---
 src/type.zig | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

(limited to 'src/type.zig')

diff --git a/src/type.zig b/src/type.zig
index 14c613a947..8e5eaf0ec7 100644
--- a/src/type.zig
+++ b/src/type.zig
@@ -5591,6 +5591,27 @@ pub const Type = extern union {
         }
     }
 
+    pub fn packedStructFieldByteOffset(ty: Type, field_index: usize, target: Target) u32 {
+        const struct_obj = ty.castTag(.@"struct").?.data;
+        assert(struct_obj.layout == .Packed);
+        comptime assert(Type.packed_struct_layout_version == 2);
+
+        var bit_offset: u16 = undefined;
+        var running_bits: u16 = 0;
+        for (struct_obj.fields.values()) |f, i| {
+            if (!f.ty.hasRuntimeBits()) continue;
+
+            if (i == field_index) {
+                bit_offset = running_bits;
+            }
+            running_bits += @intCast(u16, f.ty.bitSize(target));
+        }
+        const host_size = (running_bits + 7) / 8;
+        _ = host_size; // TODO big-endian
+        const byte_offset = bit_offset / 8;
+        return byte_offset;
+    }
+
     pub const FieldOffset = struct {
         field: usize,
         offset: u64,
-- 
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