diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 91e187574b..50da166d93 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -770,6 +770,7 @@ add_executable( zdoom WIN32
 	timidity/resample.cpp
 	timidity/timidity.cpp
 	xlat/parse_xlat.cpp
+	zscript/vmbuilder.cpp
 	zscript/vmdisasm.cpp
 	zscript/vmexec.cpp
 	zscript/vmframe.cpp
diff --git a/src/zscript/vmbuilder.cpp b/src/zscript/vmbuilder.cpp
new file mode 100644
index 0000000000..d700b99086
--- /dev/null
+++ b/src/zscript/vmbuilder.cpp
@@ -0,0 +1,413 @@
+#include "vmbuilder.h"
+
+//==========================================================================
+//
+// VMFunctionBuilder - Constructor
+//
+//==========================================================================
+
+VMFunctionBuilder::VMFunctionBuilder()
+{
+	NumIntConstants = 0;
+	NumFloatConstants = 0;
+	NumAddressConstants = 0;
+	NumStringConstants = 0;
+	MaxParam = 0;
+	ActiveParam = 0;
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder - Destructor
+//
+//==========================================================================
+
+VMFunctionBuilder::~VMFunctionBuilder()
+{
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: MakeFunction
+//
+// Creates a new VMScriptFunction out of the data passed to this class.
+//
+//==========================================================================
+
+VMScriptFunction *VMFunctionBuilder::MakeFunction()
+{
+	VMScriptFunction *func = new VMScriptFunction;
+
+	// Copy code block.
+	memcpy(func->AllocCode(Code.Size()), &Code[0], Code.Size());
+
+	// Create constant tables.
+	if (NumIntConstants > 0)
+	{
+		FillIntConstants(func->AllocKonstD(NumIntConstants));
+	}
+	if (NumFloatConstants > 0)
+	{
+		FillFloatConstants(func->AllocKonstF(NumFloatConstants));
+	}
+	if (NumAddressConstants > 0)
+	{
+		func->AllocKonstA(NumAddressConstants);
+		FillAddressConstants(func->KonstA, func->KonstATags());
+	}
+	if (NumStringConstants > 0)
+	{
+		FillStringConstants(func->AllocKonstS(NumStringConstants));
+	}
+
+	// Assign required register space.
+	func->NumRegD = IntRegisters.MostUsed;
+	func->NumRegF = FloatRegisters.MostUsed;
+	func->NumRegA = AddressRegisters.MostUsed;
+	func->NumRegS = StringRegisters.MostUsed;
+	func->MaxParam = MaxParam;
+
+	// Technically, there's no reason why we can't end the function with
+	// entries on the parameter stack, but it means the caller probably
+	// did something wrong.
+	assert(ActiveParam == 0);
+
+	return func;
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: FillIntConstants
+//
+//==========================================================================
+
+void VMFunctionBuilder::FillIntConstants(int *konst)
+{
+	TMapIterator<int, int> it(IntConstants);
+	TMap<int, int>::Pair *pair;
+
+	while (it.NextPair(pair))
+	{
+		konst[pair->Value] = pair->Key;
+	}
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: FillFloatConstants
+//
+//==========================================================================
+
+void VMFunctionBuilder::FillFloatConstants(double *konst)
+{
+	TMapIterator<double, int> it(FloatConstants);
+	TMap<double, int>::Pair *pair;
+
+	while (it.NextPair(pair))
+	{
+		konst[pair->Value] = pair->Key;
+	}
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: FillAddressConstants
+//
+//==========================================================================
+
+void VMFunctionBuilder::FillAddressConstants(FVoidObj *konst, VM_ATAG *tags)
+{
+	TMapIterator<void *, AddrKonst> it(AddressConstants);
+	TMap<void *, AddrKonst>::Pair *pair;
+
+	while (it.NextPair(pair))
+	{
+		konst[pair->Value.KonstNum].v = pair->Key;
+		tags[pair->Value.KonstNum] = pair->Value.Tag;
+	}
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: FillStringConstants
+//
+//==========================================================================
+
+void VMFunctionBuilder::FillStringConstants(FString *konst)
+{
+	TMapIterator<FString, int> it(StringConstants);
+	TMap<FString, int>::Pair *pair;
+
+	while (it.NextPair(pair))
+	{
+		konst[pair->Value] = pair->Key;
+	}
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: GetConstantInt
+//
+// Returns a constant register initialized with the given value, or -1 if
+// there were no more constants free.
+//
+//==========================================================================
+
+int VMFunctionBuilder::GetConstantInt(int val)
+{
+	int *locp = IntConstants.CheckKey(val);
+	if (locp != NULL)
+	{
+		return *locp;
+	}
+	else
+	{
+		int loc = NumIntConstants++;
+		IntConstants.Insert(val, loc);
+		return loc;
+	}
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: GetConstantFloat
+//
+// Returns a constant register initialized with the given value, or -1 if
+// there were no more constants free.
+//
+//==========================================================================
+
+int VMFunctionBuilder::GetConstantFloat(double val)
+{
+	int *locp = FloatConstants.CheckKey(val);
+	if (locp != NULL)
+	{
+		return *locp;
+	}
+	else
+	{
+		int loc = NumFloatConstants++;
+		FloatConstants.Insert(val, loc);
+		return loc;
+	}
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: GetConstantString
+//
+// Returns a constant register initialized with the given value, or -1 if
+// there were no more constants free.
+//
+//==========================================================================
+
+int VMFunctionBuilder::GetConstantString(FString val)
+{
+	int *locp = StringConstants.CheckKey(val);
+	if (locp != NULL)
+	{
+		return *locp;
+	}
+	else
+	{
+		int loc = NumStringConstants++;
+		StringConstants.Insert(val, loc);
+		return loc;
+	}
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: GetConstantAddress
+//
+// Returns a constant register initialized with the given value, or -1 if
+// there were no more constants free.
+//
+//==========================================================================
+
+int VMFunctionBuilder::GetConstantAddress(void *ptr, VM_ATAG tag)
+{
+	AddrKonst *locp = AddressConstants.CheckKey(ptr);
+	if (locp != NULL)
+	{
+		// There should only be one tag associated with a memory location.
+		assert(locp->Tag == tag);
+		return locp->KonstNum;
+	}
+	else
+	{
+		AddrKonst loc = { NumAddressConstants++, tag };
+		AddressConstants.Insert(ptr, loc);
+		return loc.KonstNum;
+	}
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: ParamChange
+//
+// Adds delta to ActiveParam and keeps track of MaxParam.
+//
+//==========================================================================
+
+void VMFunctionBuilder::ParamChange(int delta)
+{
+	assert(delta > 0 || -delta <= ActiveParam);
+	ActiveParam += delta;
+	if (ActiveParam > MaxParam)
+	{
+		MaxParam = ActiveParam;
+	}
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: RegAvailability - Constructor
+//
+//==========================================================================
+
+VMFunctionBuilder::RegAvailability::RegAvailability()
+{
+	memset(Used, 0, sizeof(Used));
+	MostUsed = 0;
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: RegAvailibity :: GetReg
+//
+// Gets one or more unused registers. If getting multiple registers, they
+// will all be consecutive. Returns -1 if there were not enough consecutive
+// registers to satisfy the request.
+//
+// Preference is given to low-numbered registers in an attempt to keep
+// the maximum register count low so as to preserve VM stack space when this
+// function is executed.
+//
+//==========================================================================
+
+int VMFunctionBuilder::RegAvailability::GetReg(int count)
+{
+	VM_UWORD mask;
+	int i, firstbit;
+
+	// Getting fewer than one register makes no sense, and
+	// the algorithm used here can only obtain ranges of up to 32 bits.
+	if (count < 1 || count > 32)
+	{
+		return -1;
+	}
+
+	mask = count == 32 ? ~0u : (1 << count) - 1;
+
+	for (i = 0; i < 256/32; ++i)
+	{
+		// Find the first word with free registers
+		VM_UWORD bits = Used[i];
+		if (bits != ~0u)
+		{
+			// Are there enough consecutive bits to satisfy the request?
+			// Search by 16, then 8, then 1 bit at a time for the first
+			// free register.
+			if ((bits & 0xFFFF) == 0xFFFF)
+			{
+				firstbit = ((bits & 0xFF0000) == 0xFF0000) ? 24 : 16;
+			}
+			else
+			{
+				firstbit = ((bits & 0xFF) == 0xFF) ? 8 : 0;
+			}
+			for (; firstbit < 32; ++firstbit)
+			{
+				if (((bits >> firstbit) & mask) == 0)
+				{
+					if (firstbit + count <= 32)
+					{ // Needed bits all fit in one word, so we got it.
+						if (firstbit + count > MostUsed)
+						{
+							MostUsed = firstbit + count;
+						}
+						Used[i] |= mask << firstbit;
+						return i * 32 + firstbit;
+					}
+					// Needed bits span two words, so check the next word.
+					else if (i < 256/32 - 1)
+					{ // There is a next word.
+						if (((Used[i + 1]) & (mask >> (32 - firstbit))) == 0)
+						{ // The next word has the needed open space, too.
+							if (firstbit + count > MostUsed)
+							{
+								MostUsed = firstbit + count;
+							}
+							Used[i] |= mask << firstbit;
+							Used[i + 1] |= mask >> (32 - firstbit);
+							return i * 32 + firstbit;
+						}
+						else
+						{ // Skip to the next word, because we know we won't find
+						  // what we need if we stay inside this one. All bits
+						  // from firstbit to the end of the word are 0. If the
+						  // next word does not start with the x amount of 0's, we
+						  // need to satisfy the request, then it certainly won't
+						  // have the x+1 0's we would need if we started at
+						  // firstbit+1 in this one.
+							firstbit = 32;
+						}
+					}
+					else
+					{ // Out of words.
+						break;
+					}
+				}
+			}
+		}
+	}
+	// No room!
+	return -1;
+}
+
+//==========================================================================
+//
+// VMFunctionBuilder :: RegAvailibity :: ReturnReg
+//
+// Marks a range of registers as free again.
+//
+//==========================================================================
+
+void VMFunctionBuilder::RegAvailability::ReturnReg(int reg, int count)
+{
+	assert(count >= 1 && count <= 32);
+	assert(reg >= 0 && reg + count <= 256);
+
+	VM_UWORD mask, partialmask;
+	int firstword, firstbit;
+
+	mask = count == 32 ? ~0u : (1 << count) - 1;
+	firstword = reg / 32;
+	firstbit = reg & 31;
+
+	if (firstbit + count <= 32)
+	{ // Range is all in one word.
+		mask <<= firstbit;
+		// If we are trying to return registers that are already free,
+		// it probably means that the caller messed up somewhere.
+		assert((Used[firstword] & mask) == mask);
+		Used[firstword] &= ~mask;
+	}
+	else
+	{ // Range is in two words.
+		partialmask = mask << firstbit;
+		assert((Used[firstword] & partialmask) == partialmask);
+		Used[firstword] &= ~partialmask;
+
+		partialmask = mask >> (32 - firstbit);
+		assert((Used[firstword + 1] & partialmask) == partialmask);
+		Used[firstword + 1] &= ~partialmask;
+	}
+}
+
+void VMFunctionBuilder::RegAvailability::Dump()
+{
+	Printf("%032B %032B %032B %032B\n%032B %032B %032B %032B\n",
+		Used[0], Used[1], Used[2], Used[3], Used[4], Used[5], Used[6], Used[7]);
+}
diff --git a/src/zscript/vmbuilder.h b/src/zscript/vmbuilder.h
new file mode 100644
index 0000000000..95d6f9dd33
--- /dev/null
+++ b/src/zscript/vmbuilder.h
@@ -0,0 +1,77 @@
+#ifndef VMUTIL_H
+#define VMUTIL_H
+
+#include "vm.h"
+
+class VMFunctionBuilder
+{
+public:
+	// Keeps track of which registers are available by way of a bitmask table.
+	class RegAvailability
+	{
+	public:
+		RegAvailability();
+		int GetReg(int count);		// Returns the first register in the range
+		void ReturnReg(int reg, int count);
+		void Dump();
+
+	private:
+		VM_UWORD Used[256/32];		// Bitmap of used registers (bit set means reg is used)
+		int MostUsed;
+
+		friend class VMFunctionBuilder;
+	};
+
+	VMFunctionBuilder();
+	~VMFunctionBuilder();
+
+	VMScriptFunction *MakeFunction();
+
+	// Returns the constant register holding the value.
+	int GetConstantInt(int val);
+	int GetConstantFloat(double val);
+	int GetConstantAddress(void *ptr, VM_ATAG tag);
+	int GetConstantString(FString str);
+
+	// Returns the address of the newly-emitted instruction.
+	size_t Emit(int opcode, int opa, int opb, int opc);
+
+	// Write out complete constant tables.
+	void FillIntConstants(int *konst);
+	void FillFloatConstants(double *konst);
+	void FillAddressConstants(FVoidObj *konst, VM_ATAG *tags);
+	void FillStringConstants(FString *strings);
+
+	// PARAM increases ActiveParam; CALL decreases it.
+	void ParamChange(int delta);
+
+	// Track available registers.
+	RegAvailability IntRegisters;
+	RegAvailability FloatRegisters;
+	RegAvailability AddressRegisters;
+	RegAvailability StringRegisters;
+
+private:
+	struct AddrKonst
+	{
+		int KonstNum;
+		VM_ATAG Tag;
+	};
+	// These map from the constant value to its position in the constant table.
+	TMap<int, int> IntConstants;
+	TMap<double, int> FloatConstants;
+	TMap<void *, AddrKonst> AddressConstants;
+	TMap<FString, int> StringConstants;
+
+	int NumIntConstants;
+	int NumFloatConstants;
+	int NumAddressConstants;
+	int NumStringConstants;
+
+	int MaxParam;
+	int ActiveParam;
+
+	TArray<VM_UBYTE> Code;
+};
+
+#endif
diff --git a/zdoom.vcproj b/zdoom.vcproj
index cbe559734b..9e7256cb30 100644
--- a/zdoom.vcproj
+++ b/zdoom.vcproj
@@ -6449,6 +6449,14 @@
 				RelativePath=".\src\zscript\vm.h"
 				>
 			</File>
+			<File
+				RelativePath=".\src\zscript\vmbuilder.cpp"
+				>
+			</File>
+			<File
+				RelativePath=".\src\zscript\vmbuilder.h"
+				>
+			</File>
 			<File
 				RelativePath=".\src\zscript\vmdisasm.cpp"
 				>