[Arm64] Revise per comments

Author: sdmaclea

src/jit/emit.cpp

@@ -1381,10 +1381,6 @@ void* emitter::emitAllocInstr(size_t sz, emitAttr opsz)
         id->idOpSize(EA_SIZE(opsz));
     }
 
-#ifdef _TARGET_ARM64_
-    id->idGCrefReg2(GCT_NONE);
-#endif
-
     // Amd64: ip-relative addressing is supported even when not generating relocatable ngen code
     if (EA_IS_DSP_RELOC(opsz)
 #ifndef _TARGET_AMD64_

src/jit/emit.h

@@ -655,9 +655,6 @@ class emitter
         // unnecessarily since the GC-ness of the second register is only needed for call instructions.
         // The instrDescCGCA struct's member keeping the GC-ness of the first return register is _idcSecondRetRegGCType.
         GCtype _idGCref : 2; // GCref operand? (value is a "GCtype")
-#ifdef _TARGET_ARM64_
-        GCtype _idGCref2 : 2;
-#endif
 
         // Note that we use the _idReg1 and _idReg2 fields to hold
         // the live gcrefReg mask for the call instructions on x86/x64
@@ -671,7 +668,7 @@ class emitter
         // x86:   30 bits
         // amd64: 38 bits
         // arm:   32 bits
-        // arm64: 32 bits
+        // arm64: 30 bits
         CLANG_FORMAT_COMMENT_ANCHOR;
 
 #if HAS_TINY_DESC
@@ -721,8 +718,8 @@ class emitter
 #define ID_EXTRA_BITFIELD_BITS (16)
 
 #elif defined(_TARGET_ARM64_)
-// For Arm64, we have used 18 bits from the second DWORD.
-#define ID_EXTRA_BITFIELD_BITS (18)
+// For Arm64, we have used 16 bits from the second DWORD.
+#define ID_EXTRA_BITFIELD_BITS (16)
 #elif defined(_TARGET_XARCH_) && !defined(LEGACY_BACKEND)
 // For xarch !LEGACY_BACKEND, we have used 14 bits from the second DWORD.
 #define ID_EXTRA_BITFIELD_BITS (14)
@@ -738,7 +735,7 @@ class emitter
         // x86:   38 bits  // if HAS_TINY_DESC is not defined (which it is)
         // amd64: 46 bits
         // arm:   48 bits
-        // arm64: 50 bits
+        // arm64: 48 bits
         CLANG_FORMAT_COMMENT_ANCHOR;
 
         unsigned _idCnsReloc : 1; // LargeCns is an RVA and needs reloc tag
@@ -751,7 +748,7 @@ class emitter
         // x86:   40 bits
         // amd64: 48 bits
         // arm:   50 bits
-        // arm64: 52 bits
+        // arm64: 50 bits
         CLANG_FORMAT_COMMENT_ANCHOR;
 
 #define ID_EXTRA_BITS (ID_EXTRA_RELOC_BITS + ID_EXTRA_BITFIELD_BITS)
@@ -767,7 +764,7 @@ class emitter
         // x86:   24 bits
         // amd64: 16 bits
         // arm:   14 bits
-        // arm64: 12 bits
+        // arm64: 14 bits
 
         unsigned _idSmallCns : ID_BIT_SMALL_CNS;
 
@@ -926,8 +923,10 @@ class emitter
             struct
             {
 #ifdef _TARGET_ARM64_
+                // For 64-bit architecture this 32-bit structure can pack with these unsigned bit fields
                 emitLclVarAddr iiaLclVar;
                 unsigned       _idReg3Scaled : 1; // Reg3 is scaled by idOpSize bits
+                GCtype         _idGCref2 : 2;
 #endif
                 regNumber _idReg3 : REGNUM_BITS;
                 regNumber _idReg4 : REGNUM_BITS;
@@ -1081,11 +1080,15 @@ class emitter
 #ifdef _TARGET_ARM64_
         GCtype idGCrefReg2() const
         {
-            return (GCtype)_idGCref2;
+            assert(!idIsTiny());
+            assert(!idIsSmallDsc());
+            return (GCtype)idAddr()->_idGCref2;
         }
         void idGCrefReg2(GCtype gctype)
         {
-            _idGCref2 = gctype;
+            assert(!idIsTiny());
+            assert(!idIsSmallDsc());
+            idAddr()->_idGCref2 = gctype;
         }
 #endif // _TARGET_ARM64_
 

src/jit/emitarm64.cpp

@@ -5368,19 +5368,18 @@ void emitter::emitIns_R_R_R_I(instruction ins,
     id->idReg2(reg2);
     id->idReg3(reg3);
 
+    // Record the attribute for the second register in the pair
+    id->idGCrefReg2(GCT_NONE);
     if (attrReg2 != EA_UNKNOWN)
     {
+        // Record the attribute for the second register in the pair
         assert((fmt == IF_LS_3B) || (fmt == IF_LS_3C));
         if (EA_IS_GCREF(attrReg2))
         {
-            /* A special value indicates a GCref pointer value */
-
             id->idGCrefReg2(GCT_GCREF);
         }
         else if (EA_IS_BYREF(attrReg2))
         {
-            /* A special value indicates a Byref pointer value */
-
             id->idGCrefReg2(GCT_BYREF);
         }
     }
@@ -6176,18 +6175,19 @@ void emitter::emitIns_R_R_S_S(
     id->idInsFmt(fmt);
     id->idInsOpt(INS_OPTS_NONE);
 
+    // Record the attribute for the second register in the pair
     if (EA_IS_GCREF(attr2))
     {
-        /* A special value indicates a GCref pointer value */
-
         id->idGCrefReg2(GCT_GCREF);
     }
     else if (EA_IS_BYREF(attr2))
     {
-        /* A special value indicates a Byref pointer value */
-
         id->idGCrefReg2(GCT_BYREF);
     }
+    else
+    {
+        id->idGCrefReg2(GCT_NONE);
+    }
 
     id->idReg1(reg1);
     id->idReg2(reg2);
@@ -6401,18 +6401,19 @@ void emitter::emitIns_S_S_R_R(
     id->idInsFmt(fmt);
     id->idInsOpt(INS_OPTS_NONE);
 
+    // Record the attribute for the second register in the pair
     if (EA_IS_GCREF(attr2))
     {
-        /* A special value indicates a GCref pointer value */
-
         id->idGCrefReg2(GCT_GCREF);
     }
     else if (EA_IS_BYREF(attr2))
     {
-        /* A special value indicates a Byref pointer value */
-
         id->idGCrefReg2(GCT_BYREF);
     }
+    else
+    {
+        id->idGCrefReg2(GCT_NONE);
+    }
 
     id->idReg1(reg1);
     id->idReg2(reg2);