Simple Code Generation
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Code Generation: Generating JVM Code for Simple Expressions and Assignments, Study notes of Computer Science
An overview of the code generation process for simple expressions and assignments in the context of java virtual machine (jvm) code. It covers the generation of code for various types of expressions, including conditionals, variable declarations, and assignments. The document also includes examples of jvm code for simple arithmetic operations and conditional statements.
Typology: Study notes
Pre 2010
1 / 8
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Simple Code Generation
“Translation”
1.Evaluate
(^) Exp .
2.If (^) Exp (^) is zero go to step 5.
3.Evaluate
(^) ans (^) ← (^) Exp .
5.Evaluate4.Go to step 6.
(^) ans (^) ← (^) Exp .
6.Use the value computed in
(^) ans (^) as the result of the conditional expression.
Exp
Exp
ConditionalExprNode
Exp
Exp
Exp
Exp
Code Generation Support Routines
GenLoadLiteral(Result, Type, Value)GenLoadLocal(Result, Type, Offset),GenLoadGlobal(Result, Type, Label)FreeTemp(Address1, Adress2, ...) GetTemp(Type)
- IdentifierNode.CodeGen ( ) if Address.AccessMode = Global
then Result
(^) GenLoadGlobal(Result, Type, Address.Label)
elsif Address.AccessMode = Local
then Result
(^) GenLoadLocal(Result, Type, Address.Offset)
elsif Address.AccessMode = Literal
then if Result
(^) ≠ (^) null
then Result
(^) GenLoadLiteral(Result, Type, Address.Value)
else Result
(^) AddressNode(Literal, Address.Value)
CodeGen Example
- PlusNode.CodeGen ( ) LeftOperand.CodeGen()
RightOperand.CodeGen()
Result (^) ← (^) GenAdd(Result, Type, LeftOperand.Result, RightOperand.Result)
- FreeTemp(LeftOperand.Result, RightOperand.Result)
Following
(^) is (^) JVM (^) code (^) for (^) A+B+
(^) where (^) A is a global integer variable
with a label of
L
(^) in class (^) C and (^) B is a local integer variable assigned a local index
(an offset within the frame) of 4:
JVM Code
Comments
Generated By
getstatic
(^) C/L (^) I stackPush static integer field onto
GenLoadGlobal
iload (^4)
stackPush integer local 4 onto
GenLoadLocal
iadd
Add top two stack locations
(^) GenAdd
iconst_
stackPush integer literal 3 onto
GenLoadLiteral
iadd
Add top two stack locations
(^) GenAdd
Assignment
- AsgNode.CodeGen ( ) Source.CodeGen()
if Source.Result.AccessMode
{JumpIfTrue, JumpIfFalse}
then Result
(^) ConvertFromJumpCode (Result, Source.Result.AccessMode, Source.Result.Label)
else Result
(^) Source.Result
if Target.Address.AccessMode = Global
then GenStoreGlobal(Result, Type, Target.Address.Label, IsExpr)
else GenStoreLocal(Result, Type, Target.Address.Offset, IsExpr)
Target
Source
AsgNode
Exp
IdentifierNode
IsExpr
Assignment Example
Consider
(^) A = (^) B (^) = C (^) + (^1) where (^) A, (^) B and (^) C are local integers with frame indices of
1, 2 and 3 respectively. First,
C
(^) is evaluated. Since
B
= C
(^1) is used as an
expression, the value of
C
(^) is duplicated (and thereby preserved) so that it can
also be assigned to
(^) A. The JVM code generatde is:
iload (^) 3 ; (^) Push (^) local
(^) # (^) (C) (^) onto (^) the (^) stack
iconst_1 ;
(^) Push (^1) (^) onto (^) the (^) stack
iadd
Compute
(^) C (^) +
dup
Duplicate
C
(^) for (^) second
(^) store
istore 2 ;
(^) Store
(^) top (^) of (^) stack
(^) into (^) local
(^) # (^) (B)
istore 1 ;
(^) Store
(^) top
(^) of (^) stack
(^) into
(^) local
(^) # (^) (A)