Merge pull request #12177 from Vexu/packed-ptr

stage2 llvm: fix handling of pointer fields in packed structs

Author: andrewrk

src/codegen/llvm.zig

@@ -5149,6 +5149,11 @@ pub const FuncGen = struct {
                             const same_size_int = self.context.intType(elem_bits);
                             const truncated_int = self.builder.buildTrunc(shifted_value, same_size_int, "");
                             return self.builder.buildBitCast(truncated_int, elem_llvm_ty, "");
+                        } else if (field_ty.zigTypeTag() == .Pointer) {
+                            const elem_bits = @intCast(c_uint, field_ty.bitSize(target));
+                            const same_size_int = self.context.intType(elem_bits);
+                            const truncated_int = self.builder.buildTrunc(shifted_value, same_size_int, "");
+                            return self.builder.buildIntToPtr(truncated_int, elem_llvm_ty, "");
                         }
                         return self.builder.buildTrunc(shifted_value, elem_llvm_ty, "");
                     },
@@ -7999,7 +8004,10 @@ pub const FuncGen = struct {
                         const non_int_val = try self.resolveInst(elem);
                         const ty_bit_size = @intCast(u16, field.ty.bitSize(target));
                         const small_int_ty = self.dg.context.intType(ty_bit_size);
-                        const small_int_val = self.builder.buildBitCast(non_int_val, small_int_ty, "");
+                        const small_int_val = if (field.ty.zigTypeTag() == .Pointer)
+                            self.builder.buildPtrToInt(non_int_val, small_int_ty, "")
+                        else
+                            self.builder.buildBitCast(non_int_val, small_int_ty, "");
                         const shift_rhs = int_llvm_ty.constInt(running_bits, .False);
                         // If the field is as large as the entire packed struct, this
                         // zext would go from, e.g. i16 to i16. This is legal with

test/behavior/packed-struct.zig

@@ -413,3 +413,25 @@ test "byte-aligned field pointer offsets" {
     try S.doTheTest();
     comptime try S.doTheTest();
 }
+
+test "load pointer from packed struct" {
+    if (builtin.zig_backend == .stage2_c) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
+    if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest;
+
+    const A = struct {
+        index: u16,
+    };
+    const B = packed struct {
+        x: *A,
+        y: u32,
+    };
+    var a: A = .{ .index = 123 };
+    var b_list: []B = &.{.{ .x = &a, .y = 99 }};
+    for (b_list) |b| {
+        var i = b.x.index;
+        try expect(i == 123);
+    }
+}