Merge pull request swiftlang#68675 from drexin/wip-remove-nul

[IRGen+Runtime] Remove unnecessary null terminator in layout strings

Author: drexin

lib/IRGen/TypeLayout.cpp

@@ -396,9 +396,6 @@ class LayoutStringBuilder {
     B.fillPlaceholderWithInt(sizePlaceholder, IGM.SizeTy, refCountBytes);
 
     B.addInt64(skip);
-
-    // NUL terminator
-    B.addInt64(0);
   }
 };
 }

stdlib/public/runtime/Enum.cpp

@@ -81,7 +81,7 @@ void swift::swift_initEnumMetadataSingleCaseWithLayoutString(
 
   auto refCountBytes = _swift_refCountBytesForMetatype(payloadType);
   const size_t fixedLayoutStringSize =
-      layoutStringHeaderSize + sizeof(uint64_t) * 2;
+      layoutStringHeaderSize + sizeof(uint64_t);
 
   uint8_t *layoutStr =
       (uint8_t *)MetadataAllocator(LayoutStringTag)
@@ -99,7 +99,6 @@ void swift::swift_initEnumMetadataSingleCaseWithLayoutString(
                                       previousFieldOffset);
 
   writer.writeBytes((uint64_t)previousFieldOffset);
-  writer.writeBytes((uint64_t)0);
 
   // we mask out HasRelativePointers, because at this point they have all been
   // resolved to metadata pointers
@@ -270,8 +269,7 @@ void swift::swift_initEnumMetadataSinglePayloadWithLayoutString(
                          sizeof(size_t);     // bytes to skip if no payload case
 
   const size_t fixedLayoutStringSize =
-      layoutStringHeaderSize +
-      sizeof(uint64_t) * 2; // Last skip bytes + NUL terminator
+      layoutStringHeaderSize + sizeof(uint64_t); // Last skip bytes
 
   uint8_t *layoutStr =
       (uint8_t *)MetadataAllocator(LayoutStringTag)
@@ -308,7 +306,6 @@ void swift::swift_initEnumMetadataSinglePayloadWithLayoutString(
                                       previousFieldOffset);
 
   writer.writeBytes((uint64_t)previousFieldOffset);
-  writer.writeBytes((uint64_t)0);
 
   writer.offset = skipBytesOffset;
   writer.writeBytes(size - previousFieldOffset);
@@ -488,10 +485,10 @@ void swift::swift_initEnumMetadataMultiPayloadWithLayoutString(
                                          sizeof(size_t) +           // Extra tag byte count
                                          sizeof(size_t) * 3;        // Payload count, ref count bytes, enum size
 
-    const size_t allocationSize = fixedLayoutHeaderSize +
-                                  (numPayloads * sizeof(size_t)) +  // Payload ref count offsets
-                                  payloadRefCountBytes +
-                                  sizeof(uint64_t) * 2;             // Last skip bytes + NUL terminator
+    const size_t allocationSize =
+        fixedLayoutHeaderSize +
+        (numPayloads * sizeof(size_t)) +         // Payload ref count offsets
+        payloadRefCountBytes + sizeof(uint64_t); // Last skip bytes
 
     uint8_t *layoutStr =
         (uint8_t *)MetadataAllocator(LayoutStringTag)
@@ -503,8 +500,8 @@ void swift::swift_initEnumMetadataMultiPayloadWithLayoutString(
     uint64_t tagAndOffset = ((uint64_t)RefCountingKind::MultiPayloadEnumGeneric)
                             << 56;
 
-    size_t refCountBytes = allocationSize - layoutStringHeaderSize -
-                           (sizeof(uint64_t) * 2);
+    size_t refCountBytes =
+        allocationSize - layoutStringHeaderSize - (sizeof(uint64_t));
     writer.writeBytes(refCountBytes);
     writer.writeBytes(tagAndOffset);
     writer.writeBytes(size_t(tagCounts.numTagBytes));
@@ -538,8 +535,6 @@ void swift::swift_initEnumMetadataMultiPayloadWithLayoutString(
 
     // Last skip bytes (always 0 for enums)
     writer.writeBytes<uint64_t>(0);
-    // NUL terminator
-    writer.writeBytes<uint64_t>(0);
 
     // we mask out HasRelativePointers, because at this point they have all been
     // resolved to metadata pointers

stdlib/public/runtime/Metadata.cpp

@@ -2711,8 +2711,8 @@ void swift::swift_initStructMetadataWithLayoutString(
     refCountBytes += _swift_refCountBytesForMetatype(fieldType);
   }
 
-  const size_t fixedLayoutStringSize = layoutStringHeaderSize +
-                                       sizeof(uint64_t) * 2;
+  const size_t fixedLayoutStringSize =
+      layoutStringHeaderSize + sizeof(uint64_t);
 
   uint8_t *layoutStr =
       (uint8_t *)MetadataAllocator(LayoutStringTag)
@@ -2758,7 +2758,6 @@ void swift::swift_initStructMetadataWithLayoutString(
   }
 
   writer.writeBytes((uint64_t)previousFieldOffset);
-  writer.writeBytes((uint64_t)0);
 
   // we mask out HasRelativePointers, because at this point they have all been
   // resolved to metadata pointers