Cleanup comments and ifdefs around this_OFFSET_FLAG (#99092)

Contributes to
#35748 (comment)

Author: jkotas

src/coreclr/inc/gcinfo.h

@@ -15,22 +15,21 @@
 #include "daccess.h"
 #include "windef.h"     // For BYTE
 
-// Some declarations in this file are used on non-x86 platforms, but most are x86-specific.
-
 // Use the lower 2 bits of the offsets stored in the tables
 // to encode properties
 
 const unsigned        OFFSET_MASK  = 0x3;  // mask to access the low 2 bits
 
 //
-//  Note for untracked locals the flags allowed are "pinned" and "byref"
-//   and for tracked locals the flags allowed are "this" and "byref"
 //  Note that these definitions should also match the definitions of
 //   GC_CALL_INTERIOR and GC_CALL_PINNED in VM/gc.h
 //
 const unsigned  byref_OFFSET_FLAG  = 0x1;  // the offset is an interior ptr
 const unsigned pinned_OFFSET_FLAG  = 0x2;  // the offset is a pinned ptr
-#if !defined(TARGET_X86) || !defined(FEATURE_EH_FUNCLETS)
+#if defined(TARGET_X86) && !defined(FEATURE_EH_FUNCLETS)
+// JIT32_ENCODER has additional restriction on x86 without funclets: 
+// - for untracked locals the flags allowed are "pinned" and "byref"
+// - for tracked locals the flags allowed are "this" and "byref"
 const unsigned   this_OFFSET_FLAG  = 0x2;  // the offset is "this"
 #endif
 

src/coreclr/jit/emit.cpp

@@ -8609,9 +8609,10 @@ void emitter::emitGCvarLiveSet(int offs, GCtype gcType, BYTE* addr, ssize_t disp
 
     desc->vpdNext = nullptr;
 
-#if !defined(JIT32_GCENCODER) || !defined(FEATURE_EH_FUNCLETS)
     /* the lower 2 bits encode props about the stk ptr */
+    CLANG_FORMAT_COMMENT_ANCHOR;
 
+#if defined(JIT32_GCENCODER) && !defined(FEATURE_EH_FUNCLETS)
     if (offs == emitSyncThisObjOffs)
     {
         desc->vpdVarNum |= this_OFFSET_FLAG;

src/coreclr/jit/gcencode.cpp

@@ -4698,7 +4698,7 @@ void GCInfo::gcMakeVarPtrTable(GcInfoEncoder* gcInfoEncoder, MakeRegPtrMode mode
     // unused by alignment
     C_ASSERT((OFFSET_MASK + 1) <= sizeof(int));
 
-#ifdef DEBUG
+#if defined(DEBUG) && defined(JIT32_GCENCODER) && !defined(FEATURE_EH_FUNCLETS)
     if (mode == MAKE_REG_PTR_MODE_ASSIGN_SLOTS)
     {
         // Tracked variables can't be pinned, and the encoding takes
@@ -4712,7 +4712,7 @@ void GCInfo::gcMakeVarPtrTable(GcInfoEncoder* gcInfoEncoder, MakeRegPtrMode mode
             assert((flags & this_OFFSET_FLAG) == 0);
         }
     }
-#endif // DEBUG
+#endif
 
     // Only need to do this once, and only if we have EH.
     if ((mode == MAKE_REG_PTR_MODE_ASSIGN_SLOTS) && compiler->ehAnyFunclets())