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scriptcomp: Merge multiple MODIFY_STACK_POINTER instructions (#78)
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When the codegen produces multiple MODIFY_STACK_POINTER instructions in
a row, we instead just keep the one and modify the value. Plus some
scaffolding to make this and future changes easier

Partial fix for #70

## Testing

Test script:
```nss
void main() {
    if (1) {
        string s = "AAA";
    }
}
```
Before this change, it compiles as
```
     0  JSR, 8                                  
     6  RET                                     
     8  CONSTANT, TYPE_INTEGER, 1               
    14  JZ, 41                                  
    20  RUNSTACK_ADD, TYPE_STRING               
    22  CONSTANT, TYPE_STRING, "AAA"            
    29  ASSIGNMENT, TYPE_VOID, -8, 4            
    37  MODIFY_STACK_POINTER, -4                
    43  MODIFY_STACK_POINTER, -4                
    49  JMP, 6                                  
    55  RET 
```
and after:
```
     0  JSR, 8                                  
     6  RET                                     
     8  CONSTANT, TYPE_INTEGER, 1               
    14  JZ, 35                                  
    20  RUNSTACK_ADD, TYPE_STRING               
    22  CONSTANT, TYPE_STRING, "AAA"            
    29  ASSIGNMENT, TYPE_VOID, -8, 4            
    37  MODIFY_STACK_POINTER, -8                
    43  JMP, 6                                  
    49  RET  
```

No changelog entry for now, as it's minor on its own, but other such
things will come.

## Licence

- [x] I am licencing my change under the project's MIT licence,
including all changes to GPL-3.0 licenced parts of the codebase.
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@mtijanic
mtijanic authored Jul 15, 2023
1 parent 362e948 commit 49e66b8
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2 changes: 1 addition & 1 deletion neverwinter/nwscript/compilerapi.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ extern "C" CScriptCompiler* scriptCompApiNewCompiler(
api.TlkResolve = TlkResolve;
CScriptCompiler* instance = new CScriptCompiler(src, bin, dbg, api);
instance->SetGenerateDebuggerOutput(writeDebug);
instance->SetOptimizeBinaryCodeLength(0);
instance->SetOptimizeBinaryCodeLength(!writeDebug);
instance->SetCompileConditionalOrMain(1);
instance->SetIdentifierSpecification(lang);
instance->SetOutputAlias("scriptout");
Expand Down
5 changes: 5 additions & 0 deletions neverwinter/nwscript/native/scriptcomp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -386,6 +386,11 @@ class CScriptCompiler
int32_t InVisitGenerateCode(CScriptParseTreeNode *pNode);
int32_t PostVisitGenerateCode(CScriptParseTreeNode *pNode);

void WriteByteSwap32(char *buffer, int32_t value);
int32_t ReadByteSwap32(char *buffer);
char *EmitInstruction(uint8_t nOpCode, uint8_t nAuxCode = 0, int32_t nDataSize = 0);
void EmitModifyStackPointer(int32_t nModifyBy);

CExoString **m_ppsParseTreeFileNames;
int32_t m_nNextParseTreeFileName;
int32_t m_nCurrentParseTreeFileName;
Expand Down
157 changes: 53 additions & 104 deletions neverwinter/nwscript/native/scriptcompfinalcode.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2214,17 +2214,7 @@ int32_t CScriptCompiler::InVisitGenerateCode(CScriptParseTreeNode *pNode)

if (pNode->nIntegerData != 0)
{
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_OPCODE_LOCATION] = CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER;
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_AUXCODE_LOCATION] = 0;

// Enter the location of the variable to write to.
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_EXTRA_DATA_LOCATION] = (char) (((pNode->nIntegerData) >> 24) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+1] = (char) (((pNode->nIntegerData) >> 16) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+2] = (char) (((pNode->nIntegerData) >> 8) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+3] = (char) (((pNode->nIntegerData)) & 0x0ff);

m_nOutputCodeLength += CVIRTUALMACHINE_OPERATION_BASE_SIZE + 4;
m_aOutputCodeInstructionBoundaries.push_back(m_nOutputCodeLength);
EmitModifyStackPointer(pNode->nIntegerData);
}

if (pNode->nOperation == CSCRIPTCOMPILER_OPERATION_STATEMENT)
Expand Down Expand Up @@ -3490,17 +3480,7 @@ int32_t CScriptCompiler::PostVisitGenerateCode(CScriptParseTreeNode *pNode)

if (nStackModifier != 0)
{
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_OPCODE_LOCATION] = CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER;
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_AUXCODE_LOCATION] = 0;

// Enter the location of the variable to write to.
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_EXTRA_DATA_LOCATION] = (char) (((nStackModifier) >> 24) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+1] = (char) (((nStackModifier) >> 16) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+2] = (char) (((nStackModifier) >> 8) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+3] = (char) (((nStackModifier)) & 0x0ff);

m_nOutputCodeLength += CVIRTUALMACHINE_OPERATION_BASE_SIZE + 4;
m_aOutputCodeInstructionBoundaries.push_back(m_nOutputCodeLength);
EmitModifyStackPointer(nStackModifier);
}

// At this point we should have had the same state that we saved earlier. If we
Expand Down Expand Up @@ -4945,17 +4925,7 @@ int32_t CScriptCompiler::PostVisitGenerateCode(CScriptParseTreeNode *pNode)

if (nStackModifier != 0)
{
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_OPCODE_LOCATION] = CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER;
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_AUXCODE_LOCATION] = 0;

// Enter the location of the variable to write to.
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_EXTRA_DATA_LOCATION] = (char) (((nStackModifier) >> 24) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+1] = (char) (((nStackModifier) >> 16) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+2] = (char) (((nStackModifier) >> 8) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+3] = (char) (((nStackModifier)) & 0x0ff);

m_nOutputCodeLength += CVIRTUALMACHINE_OPERATION_BASE_SIZE + 4;
m_aOutputCodeInstructionBoundaries.push_back(m_nOutputCodeLength);
EmitModifyStackPointer(nStackModifier);
}

// MGB - August 22, 2002 - For Scripting Debugger
Expand Down Expand Up @@ -5128,19 +5098,7 @@ int32_t CScriptCompiler::PostVisitGenerateCode(CScriptParseTreeNode *pNode)


// Add the "modify stack pointer" statement so that the return value is never used again.
int32_t nStackPointer = -4;

m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_OPCODE_LOCATION] = CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER;
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_AUXCODE_LOCATION] = 0;

// Enter the location of the variable to write to.
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_EXTRA_DATA_LOCATION] = (char) (((nStackPointer) >> 24) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+1] = (char) (((nStackPointer) >> 16) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+2] = (char) (((nStackPointer) >> 8) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+3] = (char) (((nStackPointer)) & 0x0ff);

m_nOutputCodeLength += CVIRTUALMACHINE_OPERATION_BASE_SIZE + 4;
m_aOutputCodeInstructionBoundaries.push_back(m_nOutputCodeLength);
EmitModifyStackPointer(-4);
}

//////////////////////////////////////////////////
Expand All @@ -5167,17 +5125,7 @@ int32_t CScriptCompiler::PostVisitGenerateCode(CScriptParseTreeNode *pNode)
// to be moved at all!
if (nStackPointer != 0)
{
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_OPCODE_LOCATION] = CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER;
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_AUXCODE_LOCATION] = 0;

// Enter the location of the variable to write to.
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_EXTRA_DATA_LOCATION] = (char) (((nStackPointer) >> 24) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+1] = (char) (((nStackPointer) >> 16) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+2] = (char) (((nStackPointer) >> 8) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+3] = (char) (((nStackPointer)) & 0x0ff);

m_nOutputCodeLength += CVIRTUALMACHINE_OPERATION_BASE_SIZE + 4;
m_aOutputCodeInstructionBoundaries.push_back(m_nOutputCodeLength);
EmitModifyStackPointer(nStackPointer);
}

//////////////////////////////////////////////////
Expand Down Expand Up @@ -5502,17 +5450,7 @@ int32_t CScriptCompiler::PostVisitGenerateCode(CScriptParseTreeNode *pNode)

if (pNode->nIntegerData != 0)
{
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_OPCODE_LOCATION] = CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER;
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_AUXCODE_LOCATION] = 0;

// Enter the location of the variable to write to.
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_EXTRA_DATA_LOCATION] = (char) (((pNode->nIntegerData) >> 24) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+1] = (char) (((pNode->nIntegerData) >> 16) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+2] = (char) (((pNode->nIntegerData) >> 8) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+3] = (char) (((pNode->nIntegerData)) & 0x0ff);

m_nOutputCodeLength += CVIRTUALMACHINE_OPERATION_BASE_SIZE + 4;
m_aOutputCodeInstructionBoundaries.push_back(m_nOutputCodeLength);
EmitModifyStackPointer(pNode->nIntegerData);
}

// And, finally, write the JMP statement.
Expand Down Expand Up @@ -5750,18 +5688,7 @@ int32_t CScriptCompiler::PostVisitGenerateCode(CScriptParseTreeNode *pNode)
if (m_nLoopStackDepth != m_nStackCurrentDepth)
{
int32_t nStackChange = (m_nLoopStackDepth - m_nStackCurrentDepth) * 4;

m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_OPCODE_LOCATION] = CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER;
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_AUXCODE_LOCATION] = 0;

// Enter the location of the variable to write to.
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_EXTRA_DATA_LOCATION] = (char) (((nStackChange) >> 24) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+1] = (char) (((nStackChange) >> 16) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+2] = (char) (((nStackChange) >> 8 ) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+3] = (char) (((nStackChange) ) & 0x0ff);

m_nOutputCodeLength += CVIRTUALMACHINE_OPERATION_BASE_SIZE + 4;
m_aOutputCodeInstructionBoundaries.push_back(m_nOutputCodeLength);
EmitModifyStackPointer(nStackChange);
}
}
// MGB - November 8, 2002 - Start Change
Expand All @@ -5772,18 +5699,7 @@ int32_t CScriptCompiler::PostVisitGenerateCode(CScriptParseTreeNode *pNode)
if ((m_nSwitchStackDepth + 1) != m_nStackCurrentDepth)
{
int32_t nStackChange = ((m_nSwitchStackDepth + 1) - m_nStackCurrentDepth) * 4;

m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_OPCODE_LOCATION] = CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER;
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_AUXCODE_LOCATION] = 0;

// Enter the location of the variable to write to.
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_EXTRA_DATA_LOCATION] = (char) (((nStackChange) >> 24) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+1] = (char) (((nStackChange) >> 16) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+2] = (char) (((nStackChange) >> 8 ) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+3] = (char) (((nStackChange) ) & 0x0ff);

m_nOutputCodeLength += CVIRTUALMACHINE_OPERATION_BASE_SIZE + 4;
m_aOutputCodeInstructionBoundaries.push_back(m_nOutputCodeLength);
EmitModifyStackPointer(nStackChange);
}
}
// MGB - November 8, 2002 - End Change
Expand All @@ -5810,18 +5726,7 @@ int32_t CScriptCompiler::PostVisitGenerateCode(CScriptParseTreeNode *pNode)
if (m_nLoopStackDepth != m_nStackCurrentDepth)
{
int32_t nStackChange = (m_nLoopStackDepth - m_nStackCurrentDepth) * 4;

m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_OPCODE_LOCATION] = CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER;
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_AUXCODE_LOCATION] = 0;

// Enter the location of the variable to write to.
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_EXTRA_DATA_LOCATION] = (char) (((nStackChange) >> 24) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+1] = (char) (((nStackChange) >> 16) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+2] = (char) (((nStackChange) >> 8 ) & 0x0ff);
m_pchOutputCode[m_nOutputCodeLength+CVIRTUALMACHINE_EXTRA_DATA_LOCATION+3] = (char) (((nStackChange) ) & 0x0ff);

m_nOutputCodeLength += CVIRTUALMACHINE_OPERATION_BASE_SIZE + 4;
m_aOutputCodeInstructionBoundaries.push_back(m_nOutputCodeLength);
EmitModifyStackPointer(nStackChange);
}
// MGB - October 15, 2002 - End Change

Expand Down Expand Up @@ -7060,3 +6965,47 @@ int32_t CScriptCompiler::WriteDebuggerOutputToFile(CExoString sFileName)
}
return 0;
}


void CScriptCompiler::WriteByteSwap32(char *buffer, int32_t value)
{
buffer[0] = (char)((value >> 24) & 0xff);
buffer[1] = (char)((value >> 16) & 0xff);
buffer[2] = (char)((value >> 8) & 0xff);
buffer[3] = (char)((value) & 0xff);
}
int32_t CScriptCompiler::ReadByteSwap32(char *buffer)
{
return ((int32_t)buffer[0] << 24) | ((int32_t)buffer[1] << 16) | ((int32_t)buffer[2] << 8) | (int32_t)buffer[3];
}

char *CScriptCompiler::EmitInstruction(uint8_t nOpCode, uint8_t nAuxCode, int32_t nDataSize)
{
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_OPCODE_LOCATION] = nOpCode;
m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_AUXCODE_LOCATION] = nAuxCode;

char *ret = &m_pchOutputCode[m_nOutputCodeLength + CVIRTUALMACHINE_EXTRA_DATA_LOCATION];

m_nOutputCodeLength += CVIRTUALMACHINE_OPERATION_BASE_SIZE + nDataSize;
m_aOutputCodeInstructionBoundaries.push_back(m_nOutputCodeLength);

return ret;
}

void CScriptCompiler::EmitModifyStackPointer(int32_t nModifyBy)
{
if (m_bOptimizeBinarySpace) // TODO: Rename or add separate toggle?
{
int32_t last = m_aOutputCodeInstructionBoundaries[m_aOutputCodeInstructionBoundaries.size()-2];
if (m_pchOutputCode[last + CVIRTUALMACHINE_OPCODE_LOCATION] == CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER)
{
int32_t mod = ReadByteSwap32(&m_pchOutputCode[last + CVIRTUALMACHINE_EXTRA_DATA_LOCATION]);
mod += nModifyBy;
WriteByteSwap32(&m_pchOutputCode[last + CVIRTUALMACHINE_EXTRA_DATA_LOCATION], mod);
return;
}
}

char *buf = EmitInstruction(CVIRTUALMACHINE_OPCODE_MODIFY_STACK_POINTER, 0, 4);
WriteByteSwap32(buf, nModifyBy);
}

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