Add arm64 support for EnC (dotnet#69679)

This adds support for EnC on arm64. A couple of notes on the
implementation compared to x64:
- On x64 we get the fixed stack size from unwind info. However, for the
  frames we set up on arm64 for EnC it is not possible to extract the
  frame size from there because their prologs generally look like

  stp fp, lr, [sp,#-16]!
  mov fp, sp
  sub sp, sp, dotnet#144

  with unwind codes like the following:

  set_fp; mov fp, sp

  save_fplr_x #1 (0x01); tp fp, lr, [sp, #-16]!

  As can be seen, it is not possible to get the fixed stack size from
  unwind info in this case. Instead we pass it through the GC info that
  already has a section for EnC data.

- On arm64 the JIT is required to place the PSPSym at the same offset
  from caller-SP for both the main function and for funclets. Due to
  this we try to allocate the PSPSym as early as possible in the main
  function and we must take some care in funclets.  However, this
  conflicts with the EnC frame header that the JIT uses to place values
  that must be preserved on EnC transitions. This is currently
  callee-saved registers and the MonitorAcquired boolean.

  Before this change we were allocating PSPSym above (before) the
  monitor acquired boolean, but we now have to allocate MonitorAcquired
  first, particularly because the size of the preserved header cannot
  change on EnC transitions, while the PSPSym can disappear or appear.
  This changes frame allocation slightly for synchronized functions.

Author: jakobbotsch

docs/design/coreclr/botr/clr-abi.md

@@ -653,41 +653,46 @@ Edit and Continue (EnC) is a special flavor of un-optimized code. The debugger h
 
 In the current design, the JIT does not have access to the previous versions of the method and so it has to assume the worst case. EnC is designed for simplicity, not for performance of the generated code.
 
-EnC is currently enabled on x86 and x64 only, but the same principles would apply if it is ever enabled on other platforms.
+EnC is currently enabled on x86, x64 and ARM64 only, but the same principles would apply if it is ever enabled on other platforms.
 
 The following sections describe the various Edit and Continue code conventions that must be followed.
 
 ## EnC flag in GCInfo
 
-The JIT records the fact that it has followed conventions for EnC code in GC Info. On x64, this flag is implied by recording the size of the stack frame region preserved between EnC edits (`GcInfoEncoder::SetSizeOfEditAndContinuePreservedArea`). For normal methods on JIT64, the size of this region is 2 slots (saved `RBP` and return address). On RyuJIT/AMD64, the size of this region is increased to include `RSI` and `RDI`, so that `rep stos` can be used for block initialization and block moves.
+The JIT records the fact that it has followed conventions for EnC code in GC Info. On x64/ARM64, this flag is implied by recording the size of the stack frame region preserved between EnC edits (`GcInfoEncoder::SetSizeOfEditAndContinuePreservedArea`). For x64 the size of this region is increased to include `RSI` and `RDI`, so that `rep stos` can be used for block initialization and block moves. ARM64 saves only the FP and LR registers when EnC is enabled and does not use other callee saved registers.
+
+To successfully perform EnC transitions the runtime needs to know the size of the stack frames it is transitioning between. For x64 code the size can be extracted from unwind codes. This is not possible for arm64 code as the frames are set up in such a way that the unwind codes do not allow to retrieve this value. Therefore, on ARM64 the GC info contains also the size of the fixed stack frame to be used for EnC purposes.
 
 ## Allocating local variables backward
 
 This is required to preserve addresses of the existing locals when an EnC edit appends new ones. In other words, the first local must be allocated at the highest stack address. Special care has to be taken to deal with alignment. The total size of the method frame can either grow (more locals added) or shrink (fewer temps needed) after the edit. The VM zeros out newly added locals.
 
 ## Fixed set of callee-saved registers
 
-This eliminates need to deal with the different sets in the VM, and makes preservation of local addresses easier. On x64, we choose to always save `RBP` only. There are plenty of volatile registers and so lack of non-volatile registers does not impact quality of non-optimized code.
+This eliminates need to deal with the different sets in the VM, and makes preservation of local addresses easier. There are plenty of volatile registers and so lack of non-volatile registers does not heavily impact quality of non-optimized code.
+x64 currently saves RBP, RSI and RDI while ARM64 saves just FP and LR.
 
 ## EnC is supported for methods with EH
 
 However, EnC remap is not supported inside funclets. The stack layout of funclets does not matter for EnC.
 
-## Initial RSP == RBP == PSPSym
+## Considerations with regards to PSPSym
 
-This invariant allows VM to compute new value of `RBP` and PSPSym after the edit without any additional information. Location of PSPSym is found via GC info.
+As explained previously in this document, on x64 we have Initial RSP == PSPSym. For EnC methods, as we disallow remappings after localloc (see below), we furthermore have RBP == PSPSym.
+For ARM64 we have Caller SP == PSPSym and the FP points to the previously saved FP/LR pair. For EnC the JIT always sets up the stack frame so that the FP/LR pair is at Caller SP - 16 and does not save any additional callee saves.
+These invariants allow the VM to compute new value of the frame pointer and PSPSym after the edit without any additional information. Note that the frame pointer and PSPSym do not change values or location on ARM64. However, EH may be added to a function in which case a new PSPSym needs to be materialized, even on ARM64. Location of PSPSym is found via GC info.
 
 ## Localloc
 
-Localloc is allowed in EnC code, but remap is disallowed after the method has executed a localloc instruction. VM uses the invariant above (`RSP == RBP`) to detect whether localloc was executed by the method.
+Localloc is allowed in EnC code, but remap is disallowed after the method has executed a localloc instruction. VM uses the invariants above (`RSP == RBP` on x64, `FP + 16 == SP + stack size` on ARM64) to detect whether localloc was executed by the method.
 
 ## Security object
 
-This does not require any special handling by the JIT on x64. (Different from x86). The security object is copied over by the VM during remap if necessary. Location of security object is found via GC info.
+This does not require any special handling by the JIT on x64/arm64. (Different from x86). The security object is copied over by the VM during remap if necessary. Location of security object is found via GC info.
 
 ## Synchronized methods
 
-The extra state created by the JIT for synchronized methods (original `this` and lock taken flag) must be preserved during remap. The JIT stores this state in the preserved region, and increases the size of the preserved region reported in GC info accordingly.
+The extra state created by the JIT for synchronized methods (lock taken flag) must be preserved during remap. The JIT stores this state in the preserved region, and increases the size of the preserved region reported in GC info accordingly.
 
 ## Generics
 

src/coreclr/clrdefinitions.cmake

@@ -56,11 +56,11 @@ endif(CLR_CMAKE_HOST_WIN32)
 if (NOT (CLR_CMAKE_TARGET_ARCH_I386 AND CLR_CMAKE_TARGET_UNIX))
   add_compile_definitions(EnC_SUPPORTED)
 endif()
-if(CLR_CMAKE_TARGET_ARCH_AMD64 OR (CLR_CMAKE_TARGET_ARCH_I386 AND CLR_CMAKE_TARGET_WIN32))
+if(CLR_CMAKE_TARGET_ARCH_AMD64 OR CLR_CMAKE_TARGET_ARCH_I386 OR CLR_CMAKE_TARGET_ARCH_ARM64)
   if(CLR_CMAKE_TARGET_WIN32)
     add_compile_definitions(FEATURE_ENC_SUPPORTED)
   endif(CLR_CMAKE_TARGET_WIN32)
-endif(CLR_CMAKE_TARGET_ARCH_AMD64 OR (CLR_CMAKE_TARGET_ARCH_I386 AND CLR_CMAKE_TARGET_WIN32))
+endif(CLR_CMAKE_TARGET_ARCH_AMD64 OR CLR_CMAKE_TARGET_ARCH_I386 OR CLR_CMAKE_TARGET_ARCH_ARM64)
 
 # Features - please keep them alphabetically sorted
 if(CLR_CMAKE_TARGET_WIN32)

src/coreclr/debug/ee/arm64/arm64walker.cpp

@@ -127,15 +127,22 @@ BYTE*  NativeWalker::SetupOrSimulateInstructionForPatchSkip(T_CONTEXT * context,
             offset = offset | 0xFFFFFFFFFFE00000;
         }
 
+        PCODE finalAddr;
         if ((opcode & 0x80000000) != 0) //ADRP
         {
             offset = offset << 12;
-            LOG((LF_CORDB, LL_INFO100000, "Arm64Walker::Simulate opcode: %x to ADRP X%d %p\n", opcode, RegNum, offset));
+            finalAddr = (PCODE)(address + offset) & ~0xFFF;
+            LOG((LF_CORDB, LL_INFO100000, "Arm64Walker::Simulate opcode: %x to ADRP X%d %p finalAddr = %p\n", opcode, RegNum, offset, finalAddr));
         }
         else
         {
-            LOG((LF_CORDB, LL_INFO100000, "Arm64Walker::Simulate opcode: %x to ADR X%d %p\n", opcode, RegNum, offset));
+            finalAddr = (PCODE)(address + offset);
+            LOG((LF_CORDB, LL_INFO100000, "Arm64Walker::Simulate opcode: %x to ADR X%d %p finalAddr = %p\n", opcode, RegNum, offset, finalAddr));
         }
+
+        CORDbgSetInstruction((CORDB_ADDRESS_TYPE *)patchBypass, 0xd503201f); //Add Nop in buffer
+        SetReg(context, RegNum, finalAddr);
+        return patchBypass;
     }
 
     else if ((opcode & 0x3B000000) == 0x18000000) //LDR Literal (General or SIMD)

src/coreclr/gcinfo/gcinfoencoder.cpp

@@ -344,7 +344,7 @@ GcInfoSize& GcInfoSize::operator+=(const GcInfoSize& other)
     NumUntracked += other.NumUntracked;
     NumTransitions += other.NumTransitions;
     SizeOfCode += other.SizeOfCode;
-    EncPreservedSlots += other.EncPreservedSlots;
+    EncInfoSize += other.EncInfoSize;
 
     UntrackedSlotSize += other.UntrackedSlotSize;
     NumUntrackedSize += other.NumUntrackedSize;
@@ -392,7 +392,7 @@ void GcInfoSize::Log(DWORD level, const char * header)
         LogSpew(LF_GCINFO, level, "NumUntracked: %Iu\n", NumUntracked);
         LogSpew(LF_GCINFO, level, "NumTransitions: %Iu\n", NumTransitions);
         LogSpew(LF_GCINFO, level, "SizeOfCode: %Iu\n", SizeOfCode);
-        LogSpew(LF_GCINFO, level, "EncPreservedSlots: %Iu\n", EncPreservedSlots);
+        LogSpew(LF_GCINFO, level, "EncInfoSize: %Iu\n", EncInfoSize);
 
         LogSpew(LF_GCINFO, level, "---SIZES(bits)---\n");
         LogSpew(LF_GCINFO, level, "Total: %Iu\n", TotalSize);
@@ -484,6 +484,9 @@ GcInfoEncoder::GcInfoEncoder(
 
     m_StackBaseRegister = NO_STACK_BASE_REGISTER;
     m_SizeOfEditAndContinuePreservedArea = NO_SIZE_OF_EDIT_AND_CONTINUE_PRESERVED_AREA;
+#ifdef TARGET_ARM64
+    m_SizeOfEditAndContinueFixedStackFrame = 0;
+#endif
     m_ReversePInvokeFrameSlot = NO_REVERSE_PINVOKE_FRAME;
 #ifdef TARGET_AMD64
     m_WantsReportOnlyLeaf = false;
@@ -760,6 +763,13 @@ void GcInfoEncoder::SetSizeOfEditAndContinuePreservedArea( UINT32 slots )
     m_SizeOfEditAndContinuePreservedArea = slots;
 }
 
+#ifdef TARGET_ARM64
+void GcInfoEncoder::SetSizeOfEditAndContinueFixedStackFrame( UINT32 size )
+{
+    m_SizeOfEditAndContinueFixedStackFrame = size;
+}
+#endif
+
 #ifdef TARGET_AMD64
 void GcInfoEncoder::SetWantsReportOnlyLeaf()
 {
@@ -1157,7 +1167,10 @@ void GcInfoEncoder::Build()
 
     if (m_SizeOfEditAndContinuePreservedArea != NO_SIZE_OF_EDIT_AND_CONTINUE_PRESERVED_AREA)
     {
-        GCINFO_WRITE_VARL_U(m_Info1, m_SizeOfEditAndContinuePreservedArea, SIZE_OF_EDIT_AND_CONTINUE_PRESERVED_AREA_ENCBASE, EncPreservedSlots);
+        GCINFO_WRITE_VARL_U(m_Info1, m_SizeOfEditAndContinuePreservedArea, SIZE_OF_EDIT_AND_CONTINUE_PRESERVED_AREA_ENCBASE, EncInfoSize);
+#ifdef TARGET_ARM64
+        GCINFO_WRITE_VARL_U(m_Info1, m_SizeOfEditAndContinueFixedStackFrame, SIZE_OF_EDIT_AND_CONTINUE_FIXED_STACK_FRAME_ENCBASE, EncInfoSize);
+#endif
     }
 
     if (hasReversePInvokeFrame)

src/coreclr/inc/gcinfodecoder.h

@@ -238,7 +238,7 @@ enum GcInfoHeaderFlags
 #elif defined(TARGET_ARM) || defined(TARGET_ARM64) || defined(TARGET_LOONGARCH64)
     GC_INFO_HAS_TAILCALLS               = 0x80,
 #endif // TARGET_AMD64
-    GC_INFO_HAS_EDIT_AND_CONTINUE_PRESERVED_SLOTS = 0x100,
+    GC_INFO_HAS_EDIT_AND_CONTINUE_INFO = 0x100,
     GC_INFO_REVERSE_PINVOKE_FRAME = 0x200,
 
     GC_INFO_FLAGS_BIT_SIZE_VERSION_1    = 9,
@@ -547,6 +547,9 @@ class GcInfoDecoder
     UINT32  GetCodeLength();
     UINT32  GetStackBaseRegister();
     UINT32  GetSizeOfEditAndContinuePreservedArea();
+#ifdef TARGET_ARM64
+    UINT32  GetSizeOfEditAndContinueFixedStackFrame();
+#endif
     size_t  GetNumBytesRead();
 
 #ifdef FIXED_STACK_PARAMETER_SCRATCH_AREA
@@ -578,6 +581,9 @@ class GcInfoDecoder
     UINT32  m_CodeLength;
     UINT32  m_StackBaseRegister;
     UINT32  m_SizeOfEditAndContinuePreservedArea;
+#ifdef TARGET_ARM64
+    UINT32  m_SizeOfEditAndContinueFixedStackFrame;
+#endif
     ReturnKind m_ReturnKind;
 #ifdef PARTIALLY_INTERRUPTIBLE_GC_SUPPORTED
     UINT32  m_NumSafePoints;

src/coreclr/inc/gcinfoencoder.h

@@ -118,7 +118,7 @@ struct GcInfoSize
     size_t NumUntracked;
     size_t NumTransitions;
     size_t SizeOfCode;
-    size_t EncPreservedSlots;
+    size_t EncInfoSize;
 
     size_t UntrackedSlotSize;
     size_t NumUntrackedSize;
@@ -434,6 +434,9 @@ class GcInfoEncoder
 
     // Number of slots preserved during EnC remap
     void SetSizeOfEditAndContinuePreservedArea( UINT32 size );
+#ifdef TARGET_ARM64
+    void SetSizeOfEditAndContinueFixedStackFrame( UINT32 size );
+#endif
 
 #ifdef TARGET_AMD64
     // Used to only report a frame once for the leaf function/funclet
@@ -510,6 +513,9 @@ class GcInfoEncoder
     UINT32 m_CodeLength;
     UINT32 m_StackBaseRegister;
     UINT32 m_SizeOfEditAndContinuePreservedArea;
+#ifdef TARGET_ARM64
+    UINT32 m_SizeOfEditAndContinueFixedStackFrame;
+#endif
     INT32  m_ReversePInvokeFrameSlot;
     InterruptibleRange* m_pLastInterruptibleRange;
 

src/coreclr/inc/gcinfotypes.h

@@ -753,6 +753,7 @@ void FASTCALL decodeCallPattern(int         pattern,
 #define STACK_BASE_REGISTER_ENCBASE 2 // FP encoded as 0, SP as 2.
 #define SIZE_OF_STACK_AREA_ENCBASE 3
 #define SIZE_OF_EDIT_AND_CONTINUE_PRESERVED_AREA_ENCBASE 4
+#define SIZE_OF_EDIT_AND_CONTINUE_FIXED_STACK_FRAME_ENCBASE 4
 #define REVERSE_PINVOKE_FRAME_ENCBASE 6
 #define NUM_REGISTERS_ENCBASE 3
 #define NUM_STACK_SLOTS_ENCBASE 2

src/coreclr/jit/codegenarm.cpp

@@ -2454,12 +2454,16 @@ void CodeGen::genCaptureFuncletPrologEpilogInfo()
         unsigned preSpillRegArgSize                = genCountBits(regSet.rsMaskPreSpillRegs(true)) * REGSIZE_BYTES;
         genFuncletInfo.fiFunctionCallerSPtoFPdelta = preSpillRegArgSize + 2 * REGSIZE_BYTES;
 
-        regMaskTP rsMaskSaveRegs = regSet.rsMaskCalleeSaved;
-        unsigned  saveRegsCount  = genCountBits(rsMaskSaveRegs);
-        unsigned  saveRegsSize   = saveRegsCount * REGSIZE_BYTES; // bytes of regs we're saving
+        regMaskTP rsMaskSaveRegs  = regSet.rsMaskCalleeSaved;
+        unsigned  saveRegsCount   = genCountBits(rsMaskSaveRegs);
+        unsigned  saveRegsSize    = saveRegsCount * REGSIZE_BYTES; // bytes of regs we're saving
+        unsigned  saveSizeWithPSP = saveRegsSize + REGSIZE_BYTES /* PSP sym */;
+        if (compiler->lvaMonAcquired != BAD_VAR_NUM)
+        {
+            saveSizeWithPSP += TARGET_POINTER_SIZE;
+        }
         assert(compiler->lvaOutgoingArgSpaceSize % REGSIZE_BYTES == 0);
-        unsigned funcletFrameSize =
-            preSpillRegArgSize + saveRegsSize + REGSIZE_BYTES /* PSP slot */ + compiler->lvaOutgoingArgSpaceSize;
+        unsigned funcletFrameSize = preSpillRegArgSize + saveSizeWithPSP + compiler->lvaOutgoingArgSpaceSize;
 
         unsigned funcletFrameSizeAligned  = roundUp(funcletFrameSize, STACK_ALIGN);
         unsigned funcletFrameAlignmentPad = funcletFrameSizeAligned - funcletFrameSize;

src/coreclr/jit/codegenarm64.cpp

@@ -1692,6 +1692,14 @@ void CodeGen::genCaptureFuncletPrologEpilogInfo()
         saveRegsPlusPSPSize += MAX_REG_ARG * REGSIZE_BYTES;
     }
 
+    if (compiler->lvaMonAcquired != BAD_VAR_NUM && !compiler->opts.IsOSR())
+    {
+        // We furthermore allocate the "monitor acquired" bool between PSP and
+        // the saved registers because this is part of the EnC header.
+        // Note that OSR methods reuse the monitor bool created by tier 0.
+        saveRegsPlusPSPSize += compiler->lvaLclSize(compiler->lvaMonAcquired);
+    }
+
     unsigned const saveRegsPlusPSPSizeAligned = roundUp(saveRegsPlusPSPSize, STACK_ALIGN);
 
     assert(compiler->lvaOutgoingArgSpaceSize % REGSIZE_BYTES == 0);

src/coreclr/jit/codegenarmarch.cpp

@@ -4159,24 +4159,37 @@ void CodeGen::genCreateAndStoreGCInfo(unsigned codeSize,
     {
         // what we have to preserve is called the "frame header" (see comments in VM\eetwain.cpp)
         // which is:
-        //  -return address
-        //  -saved off RBP
-        //  -saved 'this' pointer and bool for synchronized methods
+        //  -return address (saved lr)
+        //  -saved off FP
+        //  -all callee-preserved registers in case of varargs
+        //  -saved bool for synchronized methods
 
-        // 4 slots for RBP + return address + RSI + RDI
-        int preservedAreaSize = 4 * REGSIZE_BYTES;
+        int preservedAreaSize = (2 + genCountBits(RBM_ENC_CALLEE_SAVED)) * REGSIZE_BYTES;
+
+        if (compiler->info.compIsVarArgs)
+        {
+            // Varargs save all int registers between saved registers and PSP.
+            preservedAreaSize += MAX_REG_ARG * REGSIZE_BYTES;
+        }
 
         if (compiler->info.compFlags & CORINFO_FLG_SYNCH)
         {
-            if (!(compiler->info.compFlags & CORINFO_FLG_STATIC))
-                preservedAreaSize += REGSIZE_BYTES;
+            // bool in synchronized methods that tracks whether the lock has been taken (takes a full pointer sized
+            // slot)
+            preservedAreaSize += TARGET_POINTER_SIZE;
 
-            preservedAreaSize += 1; // bool for synchronized methods
+            // Verify that MonAcquired bool is at the bottom of the frame header
+            assert(compiler->lvaGetCallerSPRelativeOffset(compiler->lvaMonAcquired) == -preservedAreaSize);
         }
 
         // Used to signal both that the method is compiled for EnC, and also the size of the block at the top of the
         // frame
         gcInfoEncoder->SetSizeOfEditAndContinuePreservedArea(preservedAreaSize);
+        gcInfoEncoder->SetSizeOfEditAndContinueFixedStackFrame(genTotalFrameSize());
+
+        JITDUMP("EnC info:\n");
+        JITDUMP("  EnC preserved area size = %d\n", preservedAreaSize);
+        JITDUMP("  Fixed stack frame size = %d\n", genTotalFrameSize());
     }
 
 #endif // TARGET_ARM64
@@ -4694,6 +4707,8 @@ void CodeGen::genPushCalleeSavedRegisters()
     //      |-----------------------|
     //      |Callee saved registers | // not including FP/LR; multiple of 8 bytes
     //      |-----------------------|
+    //      |    MonitorAcquired    |
+    //      |-----------------------|
     //      |        PSP slot       | // 8 bytes (omitted in NativeAOT ABI)
     //      |-----------------------|
     //      | locals, temps, etc.   |
@@ -4725,6 +4740,8 @@ void CodeGen::genPushCalleeSavedRegisters()
     //      |-----------------------|
     //      |Callee saved registers | // not including FP/LR; multiple of 8 bytes
     //      |-----------------------|
+    //      |    MonitorAcquired    |
+    //      |-----------------------|
     //      |        PSP slot       | // 8 bytes (omitted in NativeAOT ABI)
     //      |-----------------------|
     //      | locals, temps, etc.   |
@@ -4822,7 +4839,7 @@ void CodeGen::genPushCalleeSavedRegisters()
             maskSaveRegsInt &= ~(RBM_FP | RBM_LR);                        // We've already saved FP/LR
             offset = (int)compiler->compLclFrameSize + 2 * REGSIZE_BYTES; // 2 for FP/LR
         }
-        else if (totalFrameSize <= 512)
+        else if ((totalFrameSize <= 512) && !compiler->opts.compDbgEnC)
         {
             // Case #2.
             //
@@ -4956,6 +4973,7 @@ void CodeGen::genPushCalleeSavedRegisters()
             }
             else
             {
+                assert(!compiler->opts.compDbgEnC);
                 JITDUMP("Frame type 3 (save FP/LR at bottom). #outsz=%d; #framesz=%d; LclFrameSize=%d\n",
                         unsigned(compiler->lvaOutgoingArgSpaceSize), totalFrameSize, compiler->compLclFrameSize);
 
@@ -5110,15 +5128,23 @@ void CodeGen::genPushCalleeSavedRegisters()
         establishFramePointer = false;
 
         int remainingFrameSz = totalFrameSize - calleeSaveSpDelta;
-        assert(remainingFrameSz > 0);
-        assert((remainingFrameSz % 16) == 0); // this is guaranteed to be 16-byte aligned because each component --
-                                              // totalFrameSize and calleeSaveSpDelta -- is 16-byte aligned.
+        if (remainingFrameSz > 0)
+        {
+            assert((remainingFrameSz % 16) == 0); // this is guaranteed to be 16-byte aligned because each component --
+                                                  // totalFrameSize and calleeSaveSpDelta -- is 16-byte aligned.
 
-        JITDUMP("    remainingFrameSz=%d\n", remainingFrameSz);
+            JITDUMP("    remainingFrameSz=%d\n", remainingFrameSz);
 
-        // We've already established the frame pointer, so no need to report the stack pointer change to unwind info.
-        genStackPointerAdjustment(-remainingFrameSz, initReg, pInitRegZeroed, /* reportUnwindData */ false);
-        offset += remainingFrameSz;
+            // We've already established the frame pointer, so no need to report the stack pointer change to unwind
+            // info.
+            genStackPointerAdjustment(-remainingFrameSz, initReg, pInitRegZeroed, /* reportUnwindData */ false);
+            offset += remainingFrameSz;
+        }
+        else
+        {
+            // Should only have picked this frame type for EnC.
+            assert(compiler->opts.compDbgEnC);
+        }
     }
     else
     {