From 6e067dc0506c8d5342ddaa0934770f7339619d36 Mon Sep 17 00:00:00 2001
From: Veikka Tuominen <git@vexu.eu>
Date: Fri, 13 Jan 2023 17:52:54 +0200
Subject: [PATCH] llvm: do not offset packed struct field pointers if they have
 a host size

Closes #14261
---
 src/codegen/llvm.zig            | 15 ++++++++-------
 test/behavior/packed-struct.zig | 26 ++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/src/codegen/llvm.zig b/src/codegen/llvm.zig
index b7e1466a2b..05bc957bbb 100644
--- a/src/codegen/llvm.zig
+++ b/src/codegen/llvm.zig
@@ -3370,7 +3370,7 @@ pub const DeclGen = struct {
                     return llvm_int.constIntToPtr(try dg.lowerType(tv.ty));
                 },
                 .field_ptr, .opt_payload_ptr, .eu_payload_ptr, .elem_ptr => {
-                    return dg.lowerParentPtr(tv.val);
+                    return dg.lowerParentPtr(tv.val, tv.ty.ptrInfo().data.bit_offset % 8 == 0);
                 },
                 .null_value, .zero => {
                     const llvm_type = try dg.lowerType(tv.ty);
@@ -3378,7 +3378,7 @@ pub const DeclGen = struct {
                 },
                 .opt_payload => {
                     const payload = tv.val.castTag(.opt_payload).?.data;
-                    return dg.lowerParentPtr(payload);
+                    return dg.lowerParentPtr(payload, tv.ty.ptrInfo().data.bit_offset % 8 == 0);
                 },
                 else => |tag| return dg.todo("implement const of pointer type '{}' ({})", .{
                     tv.ty.fmtDebug(), tag,
@@ -3967,7 +3967,7 @@ pub const DeclGen = struct {
         return try dg.lowerDeclRefValue(.{ .ty = ptr_ty, .val = ptr_val }, decl_index);
     }
 
-    fn lowerParentPtr(dg: *DeclGen, ptr_val: Value) Error!*llvm.Value {
+    fn lowerParentPtr(dg: *DeclGen, ptr_val: Value, byte_aligned: bool) Error!*llvm.Value {
         const target = dg.module.getTarget();
         switch (ptr_val.tag()) {
             .decl_ref_mut => {
@@ -3996,7 +3996,7 @@ pub const DeclGen = struct {
             },
             .field_ptr => {
                 const field_ptr = ptr_val.castTag(.field_ptr).?.data;
-                const parent_llvm_ptr = try dg.lowerParentPtr(field_ptr.container_ptr);
+                const parent_llvm_ptr = try dg.lowerParentPtr(field_ptr.container_ptr, byte_aligned);
                 const parent_ty = field_ptr.container_ty;
 
                 const field_index = @intCast(u32, field_ptr.field_index);
@@ -4026,6 +4026,7 @@ pub const DeclGen = struct {
                     },
                     .Struct => {
                         if (parent_ty.containerLayout() == .Packed) {
+                            if (!byte_aligned) return parent_llvm_ptr;
                             const llvm_usize = dg.context.intType(target.cpu.arch.ptrBitWidth());
                             const base_addr = parent_llvm_ptr.constPtrToInt(llvm_usize);
                             // count bits of fields before this one
@@ -4072,7 +4073,7 @@ pub const DeclGen = struct {
             },
             .elem_ptr => {
                 const elem_ptr = ptr_val.castTag(.elem_ptr).?.data;
-                const parent_llvm_ptr = try dg.lowerParentPtr(elem_ptr.array_ptr);
+                const parent_llvm_ptr = try dg.lowerParentPtr(elem_ptr.array_ptr, true);
 
                 const llvm_usize = try dg.lowerType(Type.usize);
                 const indices: [1]*llvm.Value = .{
@@ -4083,7 +4084,7 @@ pub const DeclGen = struct {
             },
             .opt_payload_ptr => {
                 const opt_payload_ptr = ptr_val.castTag(.opt_payload_ptr).?.data;
-                const parent_llvm_ptr = try dg.lowerParentPtr(opt_payload_ptr.container_ptr);
+                const parent_llvm_ptr = try dg.lowerParentPtr(opt_payload_ptr.container_ptr, true);
                 var buf: Type.Payload.ElemType = undefined;
 
                 const payload_ty = opt_payload_ptr.container_ty.optionalChild(&buf);
@@ -4105,7 +4106,7 @@ pub const DeclGen = struct {
             },
             .eu_payload_ptr => {
                 const eu_payload_ptr = ptr_val.castTag(.eu_payload_ptr).?.data;
-                const parent_llvm_ptr = try dg.lowerParentPtr(eu_payload_ptr.container_ptr);
+                const parent_llvm_ptr = try dg.lowerParentPtr(eu_payload_ptr.container_ptr, true);
 
                 const payload_ty = eu_payload_ptr.container_ty.errorUnionPayload();
                 if (!payload_ty.hasRuntimeBitsIgnoreComptime()) {
diff --git a/test/behavior/packed-struct.zig b/test/behavior/packed-struct.zig
index 3baaaee3d8..e1237a578b 100644
--- a/test/behavior/packed-struct.zig
+++ b/test/behavior/packed-struct.zig
@@ -599,3 +599,29 @@ test "packed struct initialized in bitcast" {
     const t = @bitCast(u8, T{ .val = val });
     try expect(t == val);
 }
+
+test "pointer to container level packed struct field" {
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest;
+
+    const S = packed struct(u32) {
+        test_bit: bool,
+        someother_data: u12,
+        other_test_bit: bool,
+        someother_more_different_data: u12,
+        other_bits: packed struct(u6) {
+            enable_1: bool,
+            enable_2: bool,
+            enable_3: bool,
+            enable_4: bool,
+            enable_5: bool,
+            enable_6: bool,
+        },
+        var arr = [_]u32{0} ** 2;
+    };
+    @ptrCast(*S, &S.arr[0]).other_bits.enable_3 = true;
+    try expect(S.arr[0] == 0x10000000);
+}