x86_64: fix miscompilation regression in package fetching code

Author: jacobly0

src/arch/x86_64/CodeGen.zig

@@ -15050,10 +15050,11 @@ fn genSetMem(
                 .general_purpose, .segment, .x87 => @divExact(src_alias.bitSize(), 8),
                 .mmx, .sse => abi_size,
             });
+            const src_align = Alignment.fromNonzeroByteUnits(math.ceilPowerOfTwoAssert(u32, src_size));
             if (src_size > mem_size) {
                 const frame_index = try self.allocFrameIndex(FrameAlloc.init(.{
                     .size = src_size,
-                    .alignment = Alignment.fromNonzeroByteUnits(src_size),
+                    .alignment = src_align,
                 }));
                 const frame_mcv: MCValue = .{ .load_frame = .{ .index = frame_index } };
                 try (try self.moveStrategy(ty, src_alias.class(), true)).write(
@@ -15066,14 +15067,15 @@ fn genSetMem(
                 try self.genSetMem(base, disp, ty, frame_mcv, opts);
                 try self.freeValue(frame_mcv);
             } else try (try self.moveStrategy(ty, src_alias.class(), switch (base) {
-                .none => ty.abiAlignment(mod).check(@as(u32, @bitCast(disp))),
+                .none => src_align.check(@as(u32, @bitCast(disp))),
                 .reg => |reg| switch (reg) {
-                    .es, .cs, .ss, .ds => ty.abiAlignment(mod).check(@as(u32, @bitCast(disp))),
+                    .es, .cs, .ss, .ds => src_align.check(@as(u32, @bitCast(disp))),
                     else => false,
                 },
-                .frame => |frame_index| self.getFrameAddrAlignment(
-                    .{ .index = frame_index, .off = disp },
-                ).compare(.gte, ty.abiAlignment(mod)),
+                .frame => |frame_index| self.getFrameAddrAlignment(.{
+                    .index = frame_index,
+                    .off = disp,
+                }).compare(.gte, src_align),
                 .reloc => false,
             })).write(
                 self,