llvm: fix load of packed struct that was initialized through pointers

src/codegen/llvm.zig

@@ -4,7 +4,6 @@ const assert = std.debug.assert;
 const Allocator = std.mem.Allocator;
 const log = std.log.scoped(.codegen);
 const math = std.math;
-const native_endian = builtin.cpu.arch.endian();
 const DW = std.dwarf;
 
 const Builder = @import("llvm/Builder.zig");
@@ -10722,7 +10721,21 @@ pub const FuncGen = struct {
             if (isByRef(elem_ty, mod)) {
                 return self.loadByRef(ptr, elem_ty, ptr_alignment, info.flags.is_volatile);
             }
-            return self.wip.load(ptr_kind, try o.lowerType(elem_ty), ptr, ptr_alignment, "");
+            const llvm_elem_ty = try o.lowerType(elem_ty);
+            const llvm_load_ty = if (elem_ty.isAbiInt(mod))
+                try o.builder.intType(@intCast(elem_ty.abiSize(mod) * 8))
+            else
+                llvm_elem_ty;
+            const loaded = try self.wip.load(ptr_kind, llvm_load_ty, ptr, ptr_alignment, "");
+            const shifted = if (llvm_elem_ty != llvm_load_ty and o.target.cpu.arch.endian() == .Big)
+                try self.wip.bin(.lshr, loaded, try o.builder.intValue(
+                    llvm_load_ty,
+                    (elem_ty.abiSize(mod) - (std.math.divCeil(u64, elem_ty.bitSize(mod), 8) catch
+                        unreachable)) * 8,
+                ), "")
+            else
+                loaded;
+            return self.wip.conv(.unneeded, shifted, llvm_elem_ty, "");
         }
 
         const containing_int_ty = try o.builder.intType(@intCast(info.packed_offset.host_size * 8));

test/behavior/packed-struct.zig

@@ -650,3 +650,18 @@ test "bitcast back and forth" {
     try expect(s.one == s2.one);
     try expect(s.two == s2.two);
 }
+
+test "field access of packed struct smaller than its abi size inside struct initialized with rls" {
+    const S = struct {
+        ps: packed struct { x: i2, y: i2 },
+
+        fn init(cond: bool) @This() {
+            return .{ .ps = .{ .x = 0, .y = if (cond) 1 else 0 } };
+        }
+    };
+
+    var s = S.init(true);
+    // note: this bug is triggered by the == operator, expectEqual will hide it
+    try expect(@as(i2, 0) == s.ps.x);
+    try expect(@as(i2, 1) == s.ps.y);
+}