From 6f1df5b5abd9b9abd82971f40a1ad8e9465fcd8d Mon Sep 17 00:00:00 2001
From: "alexey.lysiuk" <alexey.lysiuk@gmail.com>
Date: Sat, 1 Jun 2019 16:54:24 +0300
Subject: [PATCH] - added implicit initialization of reused register variables
 in ZScript

---
 src/scripting/backend/codegen.cpp   | 47 +++++++++++++++++++++++++++--
 src/scripting/backend/vmbuilder.cpp |  4 +++
 src/scripting/backend/vmbuilder.h   |  8 +++++
 3 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/src/scripting/backend/codegen.cpp b/src/scripting/backend/codegen.cpp
index cfff89412a..c0dd7db916 100644
--- a/src/scripting/backend/codegen.cpp
+++ b/src/scripting/backend/codegen.cpp
@@ -11350,8 +11350,51 @@ ExpEmit FxLocalVariableDeclaration::Emit(VMFunctionBuilder *build)
 		{
 			if (RegNum == -1)
 			{
-				if (!(VarFlags & VARF_Out)) RegNum = build->Registers[ValueType->GetRegType()].Get(RegCount);
-				else RegNum = build->Registers[REGT_POINTER].Get(1);
+				if (!(VarFlags & VARF_Out))
+				{
+					const int regType = ValueType->GetRegType();
+					assert(regType <= REGT_TYPE);
+
+					auto& registers = build->Registers[regType];
+					RegNum = registers.Get(RegCount);
+
+					for (int reg = RegNum, end = RegNum + RegCount; reg < end; ++reg)
+					{
+						if (!registers.IsDirty(reg))
+						{
+							continue;
+						}
+
+						ScriptPosition.Message(MSG_DEBUGMSG, "Implicit initialization of variable %s\n", Name.GetChars());
+
+						switch (regType)
+						{
+						case REGT_INT:
+							build->Emit(OP_LI, reg, 0, 0);
+							break;
+
+						case REGT_FLOAT:
+							build->Emit(OP_LKF, reg, build->GetConstantFloat(0.0));
+							break;
+
+						case REGT_STRING:
+							build->Emit(OP_LKS, reg, build->GetConstantString(nullptr));
+							break;
+
+						case REGT_POINTER:
+							build->Emit(OP_LKP, reg, build->GetConstantAddress(nullptr));
+							break;
+
+						default:
+							assert(false);
+							break;
+						}
+					}
+				}
+				else
+				{
+					RegNum = build->Registers[REGT_POINTER].Get(1);
+				}
 			}
 		}
 		else
diff --git a/src/scripting/backend/vmbuilder.cpp b/src/scripting/backend/vmbuilder.cpp
index 2b3b547c59..1c27a597e6 100644
--- a/src/scripting/backend/vmbuilder.cpp
+++ b/src/scripting/backend/vmbuilder.cpp
@@ -367,6 +367,7 @@ void VMFunctionBuilder::ParamChange(int delta)
 VMFunctionBuilder::RegAvailability::RegAvailability()
 {
 	memset(Used, 0, sizeof(Used));
+	memset(Dirty, 0, sizeof(Dirty));
 	MostUsed = 0;
 }
 
@@ -493,16 +494,19 @@ void VMFunctionBuilder::RegAvailability::Return(int reg, int count)
 		// because for that case it pushes the self pointer a second time without reallocating, so it gets freed twice.
 		//assert((Used[firstword] & mask) == mask);
 		Used[firstword] &= ~mask;
+		Dirty[firstword] |= mask;
 	}
 	else
 	{ // Range is in two words.
 		partialmask = mask << firstbit;
 		assert((Used[firstword] & partialmask) == partialmask);
 		Used[firstword] &= ~partialmask;
+		Dirty[firstword] |= partialmask;
 
 		partialmask = mask >> (32 - firstbit);
 		assert((Used[firstword + 1] & partialmask) == partialmask);
 		Used[firstword + 1] &= ~partialmask;
+		Dirty[firstword + 1] |= partialmask;
 	}
 }
 
diff --git a/src/scripting/backend/vmbuilder.h b/src/scripting/backend/vmbuilder.h
index 28b6798d51..856e2afca3 100644
--- a/src/scripting/backend/vmbuilder.h
+++ b/src/scripting/backend/vmbuilder.h
@@ -37,8 +37,16 @@ public:
 		void Return(int reg, int count);
 		bool Reuse(int regnum);
 
+		bool IsDirty(int reg) const
+		{
+			const int firstword = reg / 32;
+			const int firstbit = reg & 31;
+			return Dirty[firstword] & (1 << firstbit);
+		}
+
 	private:
 		VM_UWORD Used[256/32];		// Bitmap of used registers (bit set means reg is used)
+		VM_UWORD Dirty[256/32];
 		int MostUsed;
 
 		friend class VMFunctionBuilder;