From e6a71e9e7a6c9708f568bc8a024e91bdd027cae9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Mon, 14 Apr 2025 18:40:47 +0200
Subject: [PATCH] Sema: Fix some ptr alignment checks to handle a potential ISA
 tag bit.

Closes #23570.
---
 src/Sema.zig            | 19 ++++++++++++++++---
 test/behavior/align.zig | 10 ++++++++++
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/Sema.zig b/src/Sema.zig
index 39d748c9ce..030a7c299a 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -23235,8 +23235,16 @@ 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 = .{
@@ -23752,7 +23760,12 @@ 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().?,
diff --git a/test/behavior/align.zig b/test/behavior/align.zig
index 2e015ea11f..5454fcf756 100644
--- a/test/behavior/align.zig
+++ b/test/behavior/align.zig
@@ -635,3 +635,13 @@ 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;
+}