Working with stack

2 files changed, 46 insertions, 20 deletions

diff --git a/c_compiler/src/bindings.cpp b/c_compiler/src/bindings.cpp
index ba3fdfd..7be0173 100644
--- a/c_compiler/src/bindings.cpp
+++ b/c_compiler/src/bindings.cpp
@@ -48,7 +48,7 @@ int VariableStackBindings::stackPosition(const std::string &id) const
     else return 0;
 }
 
-unsigned VariableStackBindings::currentExpressionStackPosition() const
+int VariableStackBindings::currentExpressionStackPosition() const
 {
     return expression_stack_;
 }
diff --git a/c_compiler/src/expression.cpp b/c_compiler/src/expression.cpp
index 7c0bd8b..31595b1 100644
--- a/c_compiler/src/expression.cpp
+++ b/c_compiler/src/expression.cpp
@@ -38,19 +38,23 @@ AssignmentExpression::AssignmentExpression(Expression* lhs, Expression* rhs)
 
 VariableStackBindings AssignmentExpression::printAsm(VariableStackBindings bindings) const
 {
-    // TODO
-    // the lhs is forced to have a stack position due to it being a function, array or other type of variable
-    // unsigned current_stack = bindings.currentRegister();
-    // std::cout << "Current Register: " << current_reg << std::endl;
-    // bindings.increaseRegister();
-    
+    // TODO add stack and store results in there, also for addition and multiplication.
+
+    // get the current location of lhs in the stack so that I can store result there
     int store_stack_position = lhs_->postfixStackPosition(bindings);
-    
+
+    // get the current available stack position
+    int expression_stack_position = bindings.currentExpressionStackPosition();
+
+    // evaluate rhs and get the result back at the stack position I assigned
+    // don't have to change the stack position as there is no lhs to evaluate
     rhs_->printAsm(bindings);
 
+    // now the result of the rhs will be in that stack position, so we can load it into $2
+    std::cout << "\tlw\t$2," << expression_stack_position << "($fp)" << std::endl;
+
     // we are assigning so we don't have to evaluate the lhs as it will be overwritten anyways
-    std::cout << "\tsw\t$" << 2 << "," << store_stack_position
-    << "($fp)" << std::endl;
+    std::cout << "\tsw\t$2," << store_stack_position << "($fp)" << std::endl;
     return bindings;
 }
 
@@ -63,24 +67,34 @@ AdditiveExpression::AdditiveExpression(Expression* lhs, const std::string& opera
 
 VariableStackBindings AdditiveExpression::printAsm(VariableStackBindings bindings) const
 {
+    // I can just evaluate the lhs with the same entry stack position
     lhs_->printAsm(bindings);
 
-    // move the rhs out of the way to be able to evaluate the lhs
-    std::cout << "\tmove\t$3,$2" << std::endl;
+    // store this stack position
+    int lhs_stack_position = bindings.currentExpressionStackPosition();
 
+    // now have to increase the expression stack position for the rhs
+    bindings.nextExpressionStackPosition();
     rhs_->printAsm(bindings);
 
-    // then perform the right operation
+    // now I have them evaluated at two positions in the stack and can load both into registers
+    // $2 and $3
+
+    std::cout << "\tlw\t$2," << lhs_stack_position << "($fp)" << std::endl;
+    std::cout << "\tlw\t$3," << bindings.currentExpressionStackPosition() << "($fp)" << std::endl;
     
-    // currently using signed and sub because I only have signed numbers implemented
+    // TODO currently using signed and sub because I only have signed numbers implemented
     // must update this as I add more types
     if(operation_ == "+")
-	std::cout << "\tadd\t$2,$3,$2" << std::endl;
+	std::cout << "\tadd\t$2,$2,$3" << std::endl;
     else if(operation_ == "-")
-	std::cout << "\tsub\t$2,$3,$2" << std::endl;
+	std::cout << "\tsub\t$2,$2,$3" << std::endl;
     else
 	std::cerr << "Don't recognize symbol: '" << operation_ << "'" << std::endl;
 
+    // now I have to store it back into the original stack position
+    std::cout << "\tsw\t$2," << lhs_stack_position << "($fp)" << std::endl;
+
     return bindings;
 }
 
@@ -94,17 +108,24 @@ MultiplicativeExpression::MultiplicativeExpression(Expression* lhs, const std::s
 
 VariableStackBindings MultiplicativeExpression::printAsm(VariableStackBindings bindings) const
 {
+    // I can just evaluate lhs without increasing stack count
     lhs_->printAsm(bindings);
 
-    std::cout << "\tmove\t$3,$2" << std::endl;
+    // store current stack position
+    int lhs_stack_position = bindings.currentExpressionStackPosition();
 
+    // increase stack position to store next result in
+    bindings.nextExpressionStackPosition();
     rhs_->printAsm(bindings);
 
+    std::cout << "\tlw\t$2," << lhs_stack_position << "($fp)" << std::endl;
+    std::cout << "\tlw\t$3," << bindings.currentExpressionStackPosition() << "($fp)" << std::endl;
+
     // then perform the right operation
     if(operation_ == "*")
-	std::cout << "\tmul\t$2,$3,$2" << std::endl;
+	std::cout << "\tmul\t$2,$2,$3" << std::endl;
     else if(operation_ == "/" || operation_ == "%") {
-	std::cout << "\tdiv\t$3,$2" << std::endl;
+	std::cout << "\tdiv\t$2,$3" << std::endl;
 	if(operation_ == "/")
 	    std::cout << "\tmflo\t$2" << std::endl;
 	else
@@ -112,6 +133,9 @@ VariableStackBindings MultiplicativeExpression::printAsm(VariableStackBindings b
     } else
 	std::cerr << "Don't recognize symbol '" << operation_ << "'" << std::endl;
 
+    // finally store result back into the stack position
+    std::cout << "\tsw\t$2," << lhs_stack_position << "($fp)" << std::endl;    
+
     return bindings;
 }
 
@@ -128,6 +152,8 @@ VariableStackBindings Identifier::printAsm(VariableStackBindings bindings) const
 	std::cout << "\tlw\t$2," << bindings.stackPosition(id_) << "($fp)" << std::endl;
     else
 	std::cerr << "Can't find identifier '" << id_ << "' in current scope binding" << std::endl;
+
+    std::cout << "\tsw\t$2," << bindings.currentExpressionStackPosition() << "($fp)" << std::endl;
 	
     return bindings;
 }
@@ -152,7 +178,7 @@ VariableStackBindings Constant::printAsm(VariableStackBindings bindings) const
 {
     // constant only has to load to $2 because the other expression will take care of the rest
     std::cout << "\tli\t$2," << constant_ << std::endl;
-
+    std::cout << "\tsw\t$2," << bindings.currentExpressionStackPosition() << "($fp)" << std::endl;
     return bindings;
 }