datainit.txt

来自「开放源码的编译器open watcom 1.6.0版的源代码」· 文本 代码 · 共 313 行

Plan For Data Initialization:
=============================

Initial Assumptions:
--------------------
- don't worry about array[] of size zero
- don't worry about special requirements for aggregate class initialization
- don't worry about emitting excess zeros
- treat aggregate lists as several independent initializations plus a copy
- don't worry about bit fields
- don't worry about ``char a[] = "abc";''
- don't worry about absence of braces, assume all will be provided


Combinations Of Cases To Consider:
----------------------------------
cd  = code inside function
fcd = flag once only code inside function
ecd = code outside function
dt  = initialize data
sdt = allocate special storage
zdt = initialize data to zero

                  +-----------------+-----------------+-----------------+
                  |      Scalar     |       Ctor      |    Aggregate    |
                  |  Data  |  Code  |  Data  |  Code  |  Data  |  Code  |
+-----------------+--------+--------+--------+--------+--------+--------+
| Internal Auto   |   cd   |   cd   |   cd   |   cd   | cd+sdt | cd+sdt |
+-----------------+--------+--------+--------+--------+--------+--------+
| Internal Static |   dt   | zdt+fcd|   dt   | zdt+fcd|   dt   | zdt+fcd|
+-----------------+--------+--------+--------+--------+--------+--------+
| External Static |   dt   | zdt+ecd|   dt   | zdt+ecd|   dt   | zdt+ecd|
+-----------------+--------+--------+--------+--------+--------+--------+

Distinct Cases To Implement:
----------------------------
cd 	- emit code to do init
dt	- init data
cd+sdt	- allocate special data,
	  init special data,
	  copy special data to data,
	  emit code to do init
zdt+fcd	- init data to zero,
	  allocate flag,
	  emit code to check flag,
	  emit code to set flag and do init if not flag
zdt+ecd	- init data to zero,
	  open data init function
	  emit code to do init
	  close data init function

Entry Points From Parser:
-------------------------
DataInitInit( void );
    - start of compilation
DataInitFini( void );
    - end of compilation
DataInitStart( INITIALIZE_DATA *init, DECL_INFO *dinfo );
    - start of an initialization unit
    - init is area to save initialization information
    - dinfo is declaration information about thing being inititialized
DataInitFinish( void );
    - end of an initialization unit
DataInitSimple( PTREE expr );
    - initialization of simple object
    - i.e. type-spec symbol = expression;
DataInitConstructorParms( PTREE expression-list );
    - ctor style initialization
    - i.e. type-spec symbol( expression-list );
DataInitFirst( PTREE expression );
    - start aggregate list initialization
    - i.e. type-spec symbol = { expression, expression, ... };
    - called for first expression in expression-list
DataInitNext( PTREE expression );
    - continue aggregate list initialization
    - called for each next expression in expression-list
DataInitPush( void );
    - start another level of brace nesting
DataInitPop( void );
    - end a level of brace nesting
    
   
Philosophy Of Implementation:
-----------------------------
- analysis of expressions handled by AnalyseDataInitExpr()
- allocation of special data handled by ??
- allocation of flag for once only handled by ??
- generation of code handled as follows:
	cd  = tweak parse tree and invoke EffectCtor()
	fcd = generate parse tree ?? and invoke EffectCtor()
	ecd = change function, tweak parse tree and invoke EffectCtor()
- initialization of data handled by primitives in DGFRONT.C
    DgZeroBytes( sym, offset, n	)
    	- pad n bytes of zero at sym+offset
    DgStore??( sym, value )
    	- store value of type ?? at sym
    
   
Algorithm For DataInitStart:
----------------------------
    fill in currInit structure
    allocate init structure
    set offset and size
    
    if( data item aggregate )
	target = aggregate
	state = expecting open brace
    else
	target = scalar
	state = expecting expression
    end
    
    if( within function )
	if( symbol is static )
	    form = InternalStatic;
	else
	    form = InternalAuto;
	end
    else
	form = ExternalStatic;
    end


Algorithm For DataInitFinish:
-----------------------------
    verify state expectancy
    if( nestdepth != 0 )
	abandon initialization
    end
    state = completed
    free nest
    clear currInit pointer
    

Algorithm For DataInitSimple:
-----------------------------
    verify state expectancy
    analyse expression
    switch( form )
	case InternalAuto:
	    emit code for assignment
	    break;
	case InternalStatic:
	    if( linker constant )
		emit data
	    else
		set storage to zero
		allocate bss flag storage
		emit flag once only code
		emit code for assignment
	    end
	    break;
	case ExternalStatic:
	    if( linker constant )
		emit data
	    else
		set storage to zero
		CgFrontModuleInitOpen()
		emit code for assignment
		CgFrontModuleInitClose()
	    end
	    break;
    end
    state = expecting finish;
	

Algorithm For DataInitConstructorParms:
---------------------------------------
    verify state expectancy
    analyse expression
    switch( form )
	case InternalAuto:
	    emit code for assignment
	    break;
	case InternalStatic:
	    if( linker constant )
		emit data
	    else
		set storage to zero
		allocate bss flag storage
		emit flag once only code
		emit code for assignment
	    end
	    break;
	case ExternalStatic:
	    if( linker constant )
		emit data
	    else
		set storage to zero
		CgFrontModuleInitOpen()
		emit code for assignment
		CgFrontModuleInitClose()
	    end
	    break;
    end
    state = expecting finish;


Algorithm For DataInitFirst:
----------------------------
    verify state expectancy
    analyse expression
    switch( form )
	case InternalAuto:
	    if( linker constant )
		emit data into special
		emit code for copy from special to local
	    else
		emit zero into special
		emit code for assignment to local
	    end
	    break;
	case InternalStatic:
	    if( linker constant )
		emit data
	    else
		set storage to zero
		allocate bss flag storage
		emit flag once only code
		emit code for assignment
	    end
	    break;
	case ExternalStatic:
	    if( linker constant )
		emit data
	    else
		set storage to zero
		CgFrontModuleInitOpen()
		emit code for assignment
		CgFrontModuleInitClose()
	    end
	    break;
    end
    update offset
    if( offset < size )
	state = expecting next expression;
    else
	state = expecting close brace;
    end


Algorithm For DataInitNext:
---------------------------
    verify state expectancy
    analyse expression
    switch( form )
	case InternalAuto:
	    if( linker constant )
		emit data into special
		emit code for copy from special to local
	    else
		emit zero into special
		emit code for assignment to local
	    end
	    break;
	case InternalStatic:
	    if( linker constant )
		emit data
	    else
		set storage to zero
		allocate bss flag storage
		emit flag once only code
		emit code for assignment
	    end
	    break;
	case ExternalStatic:
	    if( linker constant )
		emit data
	    else
		set storage to zero
		CgFrontModuleInitOpen()
		emit code for assignment
		CgFrontModuleInitClose()
	    end
	    break;
    end
    update offset
    if( offset < size )
	state = expecting next expression;
    else
	state = expecting close brace;
    end


Algorithm For DataInitPush:
---------------------------
    verify state expectancy
    allocate newinit structure
    set newinit size and offset based on existing init
    push existing init
    state = expecting first expression


Algorithm For DataInitPop:
--------------------------
    verify state expectancy
    pad any required zeros
    free init structure
    pop init structure
    update init structure offset
    
    if( offset < size )
	state = expecting first expression
    else
	if( nesting > 1 )
	    state = expecting close brace
	else
	    state = expecting finish
	end
    end