refactor: centralize libc declarations, move '&' concat into StringHandler

CodeGen declares its own MallocFunc in SetupExternalFunctions and uses
it for char->STRING coercion and INPUT STRING buffers, removing two bare
getFunction("malloc") calls that null-deref'd if no handler happened to
declare malloc first. The CHR branch reuses the char->STRING coercion
path instead of a second hand-rolled heap wrapper.

String concatenation moves from ArithmeticHandler (which re-declared
four externs per '&' and was the LLVM 19 build-pin root cause) to
StringHandler::emitConcat; ArithmeticHandler no longer touches the
Module. Dead FreeFunc declarations removed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

4 files changed, 33 insertions, 55 deletions

diff --git a/lib/CodeGen/ArithmeticHandler.cc b/lib/CodeGen/ArithmeticHandler.cc
index b909abc..bfee395 100644
--- a/lib/CodeGen/ArithmeticHandler.cc
+++ b/lib/CodeGen/ArithmeticHandler.cc
@@ -11,32 +11,6 @@ Value *ArithmeticHandler::emitBinaryOp(int Op, Value *LHS, Value *RHS, int Line)
     bool LIsDouble = LHS->getType()->isDoubleTy();
     bool RIsDouble = RHS->getType()->isDoubleTy();
 
-    if (Op == '&') {
-        Module *M = Builder.GetInsertBlock()->getParent()->getParent();
-
-        FunctionType *StrLenTy = FunctionType::get(Type::getInt64Ty(Context), {PointerType::getUnqual(Context)}, false);
-        FunctionCallee StrLenF = M->getOrInsertFunction("strlen", StrLenTy);
-
-        FunctionType *MallocTy = FunctionType::get(PointerType::getUnqual(Context), {Type::getInt64Ty(Context)}, false);
-        FunctionCallee MallocF = M->getOrInsertFunction("malloc", MallocTy);
-
-        FunctionType *StrCpyTy = FunctionType::get(PointerType::getUnqual(Context), {PointerType::getUnqual(Context), PointerType::getUnqual(Context)}, false);
-        FunctionCallee StrCpyF = M->getOrInsertFunction("strcpy", StrCpyTy);
-        FunctionCallee StrCatF = M->getOrInsertFunction("strcat", StrCpyTy);
-
-        Value *LLen = Builder.CreateCall(StrLenF, {LHS}, "llen");
-        Value *RLen = Builder.CreateCall(StrLenF, {RHS}, "rlen");
-        Value *TotalLen = Builder.CreateAdd(LLen, RLen, "totallen");
-        Value *AllocSize = Builder.CreateAdd(TotalLen, ConstantInt::get(Type::getInt64Ty(Context), 1), "allocsize");
-
-        Value *NewStr = Builder.CreateCall(MallocF, {AllocSize}, "concat_str");
-
-        Builder.CreateCall(StrCpyF, {NewStr, LHS});
-        Builder.CreateCall(StrCatF, {NewStr, RHS});
-
-        return NewStr;
-    }
-
     if (Op == '/') {
         Value *LVal = LHS;
         Value *RVal = RHS;
diff --git a/lib/CodeGen/ArrayHandler.cc b/lib/CodeGen/ArrayHandler.cc
index aa7230a..af16692 100644
--- a/lib/CodeGen/ArrayHandler.cc
+++ b/lib/CodeGen/ArrayHandler.cc
@@ -32,11 +32,6 @@ void ArrayHandler::setupExternalFunctions() {
 
     FunctionType *MallocType = FunctionType::get(PointerType::getUnqual(*TheContext), MallocArgs, false);
     MallocFunc = TheModule->getOrInsertFunction("malloc", MallocType);
-
-    std::vector<Type*> FreeArgs;
-    FreeArgs.push_back(PointerType::getUnqual(*TheContext));
-    FunctionType *FreeType = FunctionType::get(Type::getVoidTy(*TheContext), FreeArgs, false);
-    FreeFunc = TheModule->getOrInsertFunction("free", FreeType);
 }
 
 const ArrayMetadata *ArrayHandler::getMetadata(const std::string &Name) const {
diff --git a/lib/CodeGen/CodeGen.cc b/lib/CodeGen/CodeGen.cc
index 1c019d9..de64a15 100644
--- a/lib/CodeGen/CodeGen.cc
+++ b/lib/CodeGen/CodeGen.cc
@@ -99,6 +99,11 @@ void CodeGen::SetupExternalFunctions() {
     FunctionType *ScanfType = FunctionType::get(Type::getInt32Ty(*TheContext), PrintfArgs, true);
     ScanfFunc = TheModule->getOrInsertFunction("scanf", ScanfType);
 
+    FunctionType *MallocType = FunctionType::get(PointerType::getUnqual(*TheContext),
+                                                 {Type::getInt64Ty(*TheContext)},
+                                                 false);
+    MallocFunc = TheModule->getOrInsertFunction("malloc", MallocType);
+
     PrintfFormatStr = Builder->CreateGlobalStringPtr("%lld\n", "fmt_nl", 0, TheModule.get());
     PrintfFloatFormatStr = Builder->CreateGlobalStringPtr("%f\n", "fmt_flt", 0, TheModule.get());
     PrintfStringFormatStr = Builder->CreateGlobalStringPtr("%s\n", "fmt_str", 0, TheModule.get());
@@ -291,17 +296,7 @@ Value *CodeGen::coerceValueToType(Value *Val, const TypeInfo *TargetInfo) {
                 return StrConvHandler->emitNumToStr(Val, true);
             }
             if (Val->getType()->isIntegerTy(8)) {
-                Function *MallocF = TheModule->getFunction("malloc");
-                if (!MallocF) {
-                    FunctionType *MallocTy = FunctionType::get(PointerType::getUnqual(*TheContext),
-                                                               {Type::getInt64Ty(*TheContext)},
-                                                               false);
-                    MallocF = Function::Create(MallocTy,
-                                               Function::ExternalLinkage,
-                                               "malloc",
-                                               TheModule.get());
-                }
-                Value *Mem = Builder->CreateCall(MallocF,
+                Value *Mem = Builder->CreateCall(MallocFunc,
                                                  ConstantInt::get(*TheContext, APInt(64, 2)),
                                                  "char_str");
                 Builder->CreateStore(Val, Mem);
@@ -511,6 +506,9 @@ Value *CodeGen::emitExpr(ExprAST *Expr) {
         Value *L = emitExpr(Bin->getLHS());
         Value *R = emitExpr(Bin->getRHS());
         if (!L || !R) return nullptr;
+        if (Bin->getOp() == '&') {
+            return StrHandler->emitConcat(L, R);
+        }
         return ArithHandler->emitBinaryOp(Bin->getOp(), L, R, Bin->getLine());
     }
 
@@ -565,14 +563,7 @@ Value *CodeGen::emitExpr(ExprAST *Expr) {
         if (Name == "CHR") {
             Value *IntVal = coerceValueToType(emitExpr(Call->getArgs()[0].get()), resolveType("INTEGER"));
             Value *CharVal = ChrHandler->emitChr(IntVal);
-            Function *MallocF = TheModule->getFunction("malloc");
-            Value *Mem = Builder->CreateCall(MallocF, ConstantInt::get(*TheContext, APInt(64, 2)));
-            Builder->CreateStore(CharVal, Mem);
-            Value *NullPtr = Builder->CreateInBoundsGEP(Type::getInt8Ty(*TheContext),
-                                                        Mem,
-                                                        ConstantInt::get(*TheContext, APInt(64, 1)));
-            Builder->CreateStore(ConstantInt::get(Type::getInt8Ty(*TheContext), 0), NullPtr);
-            return Mem;
+            return coerceValueToType(CharVal, resolveType("STRING"));
         }
         if (Name == "IS_NUM") {
             return StrConvHandler->emitIsNum(emitExpr(Call->getArgs()[0].get()));
@@ -873,8 +864,7 @@ void CodeGen::emitStmt(StmtAST *Stmt) {
             Value *BoolVal = Builder->CreateICmpNE(Val, ConstantInt::get(*TheContext, APInt(64, 0)), "bool_cast");
             Builder->CreateStore(BoolVal, Info->Storage);
         } else if (TypeInfo->isString()) {
-            Function *MallocF = TheModule->getFunction("malloc");
-            Value *Mem = Builder->CreateCall(MallocF, ConstantInt::get(*TheContext, APInt(64, 1024)), "input_str");
+            Value *Mem = Builder->CreateCall(MallocFunc, ConstantInt::get(*TheContext, APInt(64, 1024)), "input_str");
             Args.push_back(ScanfStringFormatStr);
             Args.push_back(Mem);
             Builder->CreateCall(ScanfFunc, Args);
diff --git a/lib/CodeGen/StringHandler.cc b/lib/CodeGen/StringHandler.cc
index e5971d0..56b5aea 100644
--- a/lib/CodeGen/StringHandler.cc
+++ b/lib/CodeGen/StringHandler.cc
@@ -16,9 +16,6 @@ void StringHandler::setupExternalFunctions() {
     FunctionType *MallocType = FunctionType::get(PointerType::getUnqual(Context), {Type::getInt64Ty(Context)}, false);
     MallocFunc = Module.getOrInsertFunction("malloc", MallocType);
 
-    FunctionType *FreeType = FunctionType::get(Type::getVoidTy(Context), {PointerType::getUnqual(Context)}, false);
-    FreeFunc = Module.getOrInsertFunction("free", FreeType);
-
     FunctionType *StrLenType = FunctionType::get(Type::getInt64Ty(Context), {PointerType::getUnqual(Context)}, false);
     StrLenFunc = Module.getOrInsertFunction("strlen", StrLenType);
 
@@ -26,6 +23,12 @@ void StringHandler::setupExternalFunctions() {
     FunctionType *MemCpyType = FunctionType::get(PointerType::getUnqual(Context), MemCpyArgs, false);
     MemCpyFunc = Module.getOrInsertFunction("memcpy", MemCpyType);
 
+    FunctionType *StrCpyType = FunctionType::get(PointerType::getUnqual(Context),
+                                                 {PointerType::getUnqual(Context), PointerType::getUnqual(Context)},
+                                                 false);
+    StrCpyFunc = Module.getOrInsertFunction("strcpy", StrCpyType);
+    StrCatFunc = Module.getOrInsertFunction("strcat", StrCpyType);
+
     FunctionType *CharCaseType = FunctionType::get(Type::getInt32Ty(Context), {Type::getInt32Ty(Context)}, false);
     ToUpperFunc = Module.getOrInsertFunction("toupper", CharCaseType);
     ToLowerFunc = Module.getOrInsertFunction("tolower", CharCaseType);
@@ -50,6 +53,22 @@ Value *StringHandler::emitLength(Value *Str) {
     return Builder.CreateCall(StrLenFunc, Str, "len");
 }
 
+Value *StringHandler::emitConcat(Value *LHS, Value *RHS) {
+    if (!LHS || !RHS) return nullptr;
+
+    Value *LLen = Builder.CreateCall(StrLenFunc, {LHS}, "llen");
+    Value *RLen = Builder.CreateCall(StrLenFunc, {RHS}, "rlen");
+    Value *TotalLen = Builder.CreateAdd(LLen, RLen, "totallen");
+    Value *AllocSize = Builder.CreateAdd(TotalLen, ConstantInt::get(Type::getInt64Ty(Context), 1), "allocsize");
+
+    Value *NewStr = Builder.CreateCall(MallocFunc, {AllocSize}, "concat_str");
+
+    Builder.CreateCall(StrCpyFunc, {NewStr, LHS});
+    Builder.CreateCall(StrCatFunc, {NewStr, RHS});
+
+    return NewStr;
+}
+
 Value *StringHandler::emitMid(Value *Str, Value *Start, Value *Len) {
     
     Value *FullLen = emitLength(Str);