Sema: Fix some ptr alignment checks to handle a potential ISA tag bit.

Closes ziglang#23570.

Author: alexrp

src/Sema.zig

@@ -22614,8 +22614,16 @@ fn ptrFromIntVal(
  const addr = try operand_val.toUnsignedIntSema(pt);
  if (!ptr_ty.isAllowzeroPtr(zcu) and addr == 0)
  return sema.fail(block, operand_src, "pointer type '{}' does not allow address zero", .{ptr_ty.fmt(pt)});
- if (addr != 0 and ptr_align != .none and !ptr_align.check(addr))
- return sema.fail(block, operand_src, "pointer type '{}' requires aligned address", .{ptr_ty.fmt(pt)});
+ if (addr != 0 and ptr_align != .none) {
+ const masked_addr = if (ptr_ty.childType(zcu).fnPtrMaskOrNull(zcu)) |mask|
+ addr & mask
+ else
+ addr;
+
+ if (!ptr_align.check(masked_addr)) {
+ return sema.fail(block, operand_src, "pointer type '{}' requires aligned address", .{ptr_ty.fmt(pt)});
+ }
+ }
 
  return switch (ptr_ty.zigTypeTag(zcu)) {
  .optional => Value.fromInterned(try pt.intern(.{ .opt = .{
@@ -23131,7 +23139,12 @@ fn ptrCastFull(
 
  if (dest_align.compare(.gt, src_align)) {
  if (try ptr_val.getUnsignedIntSema(pt)) |addr| {
- if (!dest_align.check(addr)) {
+ const masked_addr = if (Type.fromInterned(dest_info.child).fnPtrMaskOrNull(zcu)) |mask|
+ addr & mask
+ else
+ addr;
+
+ if (!dest_align.check(masked_addr)) {
  return sema.fail(block, operand_src, "pointer address 0x{X} is not aligned to {d} bytes", .{
  addr,
  dest_align.toByteUnits().?,

test/behavior/align.zig

@@ -596,3 +596,13 @@ test "function pointer @intFromPtr/@ptrFromInt roundtrip" {
 
  try std.testing.expectEqual(nothing_ptr, nothing_ptr2);
 }
+
+test "function pointer align mask" {
+ if (!(builtin.cpu.arch.isArm() or builtin.cpu.arch.isMIPS())) return error.SkipZigTest;
+
+ const a: *const fn () callconv(.c) void = @ptrFromInt(0x20202021);
+ _ = &a;
+
+ const b: *align(16) const fn () callconv(.c) void = @alignCast(a);
+ _ = &b;
+}