master: Correct some obsolete bit-masking steps

The branch "master" has been updated in SBCL:
       via  8f009e157941c12239e7ebc7a6af0cf61109f083 (commit)
      from  d3bd86dd8a65dc78e4900c539f0017ea02ad173e (commit)

- Log -----------------------------------------------------------------
commit 8f009e157941c12239e7ebc7a6af0cf61109f083
Author: Douglas Katzman <[email protected]>
Date:   Tue Apr 7 02:02:12 2026 -0400

    Correct some obsolete bit-masking steps
    
    They weren't wrong, but just overly complicated in light of earlier changes
---
 src/runtime/gencgc-impl.h    | 4 ++++
 src/runtime/immobile-space.c | 6 ++----
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/runtime/gencgc-impl.h b/src/runtime/gencgc-impl.h
index 2824a897f..3d92e3465 100644
--- a/src/runtime/gencgc-impl.h
+++ b/src/runtime/gencgc-impl.h
@@ -776,6 +776,10 @@ struct fixedobj_page { // 8 bytes per page
     union immobile_page_attr {
       int packed;
       struct {
+        // The only "flags" indicate the write-protect status. They used to
+        // also indicate the nature of objects stored on a page, distinguishing
+        // interned symbols from uninterned symbols for example.
+        // Revision 6a080ae2 did away with such usage.
         unsigned char flags;
         unsigned char obj_align; // object spacing expressed in lisp words
         unsigned char unused1;
diff --git a/src/runtime/immobile-space.c b/src/runtime/immobile-space.c
index 89038c6b5..2c603ad97 100644
--- a/src/runtime/immobile-space.c
+++ b/src/runtime/immobile-space.c
@@ -105,15 +105,13 @@ unsigned int immobile_scav_queue_count;
 #define WRITE_PROTECT_CLEARED 0x40
 
 // Packing and unpacking attributes
-// the low two flag bits are for write-protect status
 #define MAKE_ATTR(spacing) ((spacing)<<8)
 #define OBJ_SPACING(attr) ((attr>>8) & 0xFF)
 
 // Ignore the write-protect bits and the generations when comparing attributes
 #define ATTRIBUTES_MATCH_P(page_attr,specified_attr) \
-  ((page_attr & 0xFFFF3F) == specified_attr)
-#define SET_WP_FLAG(index,flag) \
-  fixedobj_pages[index].attr.parts.flags = (fixedobj_pages[index].attr.parts.flags & 0x3F) | flag
+  ((page_attr & 0xFFFF00) == specified_attr)
+#define SET_WP_FLAG(index,bits) fixedobj_pages[index].attr.parts.flags = bits
 
 #define set_page_full(i) fixedobj_pages[i].free_index = IMMOBILE_CARD_BYTES
 #define page_full_p(i) (fixedobj_pages[i].free_index >= (int)IMMOBILE_CARD_BYTES)

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