Chapter9CodeOptimizationOverviewPurposeofCodeOptimizerPlacesforPotentialImprovementsPlacesforPotentialImprovementsOrganizationofthecodeOptimizerBasicblocksAnExampleTheUseofaNameLivevariablePartitionintoBasicBlocksDeterminationofLeadersofBasicBlocksPartitionintoBasicBlocksAnExample(1)ReadX(2)ReadYFlowgraphFlowGraphFlowGraphFlowGraphLoopsLoopsLoopsDominator一棵开花的树(作者：席慕容)BackEdgeFindAlltheLoopsinaFlowGraphFindAlltheLoopsinaFlowGraphFindAlltheLoopsinaFlowGraphOptimizationofBasicBlocksCommonSubexpressionEliminationAnExample(1)Pi:=3.14(2)T1:=6.28(3)T2:=R+r(4)A:=T1*T2(5)B:=A(6)T3:=6.28(7)T4:=R+r(8)T5:=T3*T4(9)T6:=R-r(10)B:=T5*T6CopyPropagationCopyPropagation(1)Pi:=3.14(2)T1:=6.28(3)T2:=R+r(4)A:=T1*T2(5)B:=A(6)T3:=T1(7)T4:=T2(8)T5:=T1*T2(9)T6:=R-r(10)B:=T5*T6DeadCodeElimination(1)Pi:=3.14(2)T1:=6.28(3)T2:=R+r(4)A:=T1*T2(5)B:=A(6)T3:=T1(7)T4:=T2(8)T5:=T1*T2(9)T6:=R-r(10)B:=T5*T6DAGDAGDAGDAGDAGAnExamplen1FindingLocalCommonSubexpressionsAnExampleDeadCodeEliminationRepresentationofArrayReferencesRepresentationofArrayReferencesRepresentationofArrayReferencesRepresentationofArrayReferencesRepresentationofArrayReferencesAnExampleAnExampleGeneratingCodefromDagsHeuristicOrderCodeOptimizationinaLoopPre-HeadersStrengthReductionInductionVariablesInductionVariablesAnExample(1)j:=1(2)i:=1(1)j:=1(2)i:=1(1)j:=1(2)i:=1(1)j:=1(2)i:=1(1)j:=1(2)i:=1AnotherExampleAnotherExampleIntroductiontoData-FlowAnalysisProgramPointProgramPointExecutionPathExecutionPathAnExampleProgramAnalysisAnExampleTheData-FlowAnalysisSchemaTheData-FlowAnalysisSchemaTheData-FlowAnalysisSchemaTransferFunctionsData-FlowSchemasonBasicBlocksData-FlowSchemasonBasicBlocksReachingDefinitionsReachingDefinitionsDetectingPossibleUsesBeforeDefinitionDetectingPossibleUsesBeforeDefinitionInaccuracybytraversingAllPathesConservatisminData-FlowAnalysisConservatisminData-FlowAnalysisConservatisminData-FlowAnalysisTransferEquationsforReachingDefinitionsTheTransferFunctionofaBasicBlockTheTransferFunctionofaBa