Lecture 20 Types Offsets Revisited

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Lecture 20 Types / Offsets Revisited
CSCE 531 Compiler Construction

• Topics
• Procedural Abstraction
• Activation records
• Readings 8.2

March 29, 2006
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Overview

• Last Time
• Review Semantics actions for function invocation
• Review Semantics actions for arglist
• Attribute placeList list of identifiers
• Handling Function Definitions
• Todays Lecture
• Final reductions of statement lists in
  programs/functions/procedures
• Passing Parameters
• Array.c
• Nested Scope
• Nested.c
• References Section 8.2
• Homework

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Test 2 - TIME CHANGE !!!!!

• Test 2 - TIME CHANGE !!!!!
• Wednesday April 5 700PM
• First Robotics Volunteers Friday March 31,
  500-700PM
• Graduate Assistants - I need to see after class!
• AARONS,
• AL-ABRI,
• BYRNES,
• GARRETT,
• GREGORY,
• KODUR,
• SAXENA,
• TEMLYAKOV,
• VARGHESE,
• TALATAM

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Some Email Questions

• How do we handle running out of pace in quad
  arrays? Again with corrections
• When an if-then statement is last statement in
  program (or function) how do we backpatch?

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Question on size of code arrays

• What happens when you run out of space?
• Nextquad gt arraySize

void gen(int op) static int opcodeNULL
static int arraySize 0 static int nextquad
0 if (nextquad gt arraySize)
arraySize ARRAY_INCREMENT opcode (int
) realloc(opcode, arraySize)
opcodenextquad op
Need to be a globals Why?
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Final reductions of statement lists
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Precedence of Operators

• Dear Dr. Matthews
• About the operator precedence, if I have
• a b c,
• What will be the order?
• Is that first evaluate bc then a
• (bc) or first a b then (ab) c?
• Best

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C type booleans Not for Project 4!!!

• The grammar for handling the logical operator
  not
• Is B ? NOT B
• Not B ? '!' E , which would be fine in C
• /CODE FOR THE ('not' B)
  EXPRESSION/

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Parameter Passing

• Call by value
• Call by reference
• Copy-restore
• Call by name
• Logically the procedure is treated as a macro
  with the arguments substituted for the formal
  parameters
• Actually code passed for evaluating the argument
  is passed to the functions

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Declarations within Functions/Procedures

• Figure 8.11 differences in approaches
• P ? offset 0 D // place code instead
  of marker
• D ? D D
• D ? ID T enter(id.place, T.type,
  offset)
• offset offset T.width

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Types within the Declarations

• T ? integer T.type INTEGER T.width 4
• double T.type double T.width 8
  
• array num of T1
• T.type array(num.val, T1.type)
• T.width num.val T1.width
• T1 T.type pointer(T1.type)
• T.width 4

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Representing Type Information

• Type tree
• Nodes
• Leaves Base types int, float
• Interior Nodes Type Constructors
• Array (size, dimensions, type)
• or maybe array of array for 2 dimensions
• Pointer ( targetType)
• FuncReturning
• Record ( componentTypeList )

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Type Example
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Type Encoding

• Base types
• boolean 0000
• char 0001
• int 0010
• double 0011
• Type constructor encodings -
• pointer 01
• array 10
• freturns 11
• Why encode at all?

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Handling Records
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Structural and Name Equivalence of Types

• Two identifiers are name equivalent if the types
  have the same name.
• Two identifiers are structurally equivalent if
  the types have the same structure (type tree).