第6章 中间代码生成ppt课件.ppt

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1、中间代码生成1编译器的前端与后端2Methodusedfortranslationintointermediatecode:syntaxdirectedtranslation.Wewilltranslatetheconstructsofthelanguage:Declarations;AssignmentsFlow-of-controlstatementsIntermediaterepresentationintheliteratureinclude:syntaxtree(section5.2)postfix

2、(section2.3)threeaddresscode(chap.8)others(AST,DAG,ControlFlowGraphs(CFG),ProgramdependenceGraph(PDG),StaticSingleAssignmentForm,stackcode)3语法树,DAG后缀表达式可以看做语法树的一种线性表示abcuminus*bcuminus*+assign4语法树能通过语法制导定义（SDD）生成.E.g:56三地址代码形如:x:=yopz;Othertypesofthree-addr

3、essstatement7翻译时生成临时变量:x+y*zt1:=y*zt2:=x+t1DAG8生成三地址语句9表达式的三地址代码10newtemp()生成临时变量:t1,t2,…gen()生成中间代码11生成四元式ATASisanabstractformofintermediatecode.Incompiler,thesestatementscanbeimplementedasrecordshavingfieldsforoperatorandtheoperands.Recordrepresentationso

4、fthisformcomprisesquadruples,triplesandindirecttriplesTriplesareusedinordertoavoidtheenteringtemporarynamesintosymboltables.Wecanrefertoatemporaryvaluebythispositioninthestatement12E.g.Ternaryoperationx[i]:=yrequirestwoentriesinthetriplestructureandx:=y[i]r

5、equirestwooperations.13Otherrepresentations.IndirecttriplesusealistofpointerstotriplesinsteadoftriplethemselvesTheusageofdifferentrepresentationisamatterofhowmuchindirectionwewanttouseinourcompilerItcouldbeaproblemwhenweuseoptimizationinoutputcode.Movingate

6、mporarythatrepresentsastatementrequirestochangeallthereferencesinthetriples14过程声明AsymboltableentryiscreatedforeverydeclarednameInformationincludesname,type,relativeaddressofstorage,etc.Relativeaddressconsistsofanoffset:Offsetisfromthebaseofthestaticdataarea

7、forglobals,orOffsetisfromthefieldforlocaldatainanactivationrecordforlocalstoproceduresTypesareassignedattributestypeandwidthBecomesmorecomplexifweneedtodealwithnestedproceduresorrecords15Integershavewidth=4andrealshavethewidth=816KeepingTrackofscopeInformat

8、ionSomelanguageshavenestedproceduresspecification.Inthiscasewecanassignlocalnamesasinpreviousapproach.Whenisseeanestedprocedure,theprocessingofdeclarationistemporarilysuspendedPDDD;D

9、id:T

10、procid;D;SA