Live Variables Analysis PDF
Preview Live Variables Analysis
Live Variables Analysis Uday Khedker (www.cse.iitb.ac.in/˜uday) Department of Computer Science and Engineering, Indian Institute of Technology, Bombay Dec 2017 WSSE Pune Liveness Analysis: Outline 1/25 Outline • Live Variables Analysis • Strongly Live Variables Analysis • Some Observations Dec 2017 IIT Bombay Part 1 Live Variables Analysis WSSE Pune Liveness Analysis: Live Variables Analysis 2/25 Defining Live Variables Analysis A variable v is live at a program point p, if some path from p to program exit contains an r-value oc- currence of v which is not preceded by an l-value occurrence of v. Start Start Start p p p v =a∗b v =a∗b a=v+2 v =a+2 vv==v +2 End End End Dec 2017 IIT Bombay WSSE Pune Liveness Analysis: Live Variables Analysis 2/25 Defining Live Variables Analysis A variable v is live at a program point p, if some path from p to program exit contains an r-value oc- currence of v which is not preceded by an l-value occurrence of v. v is live at p Start Start Start p p p v =a∗b v =a∗b a=v+2 v =a+2 vv==v +2 End End End Dec 2017 IIT Bombay WSSE Pune Liveness Analysis: Live Variables Analysis 2/25 Defining Live Variables Analysis A variable v is live at a program point p, if some path from p to program exit contains an r-value oc- currence of v which is not preceded by an l-value occurrence of v. v is live at p v is not live at p Start Start Start p p p v =a∗b v =a∗b a=v+2 v =a+2 vv==v +2 End End End Dec 2017 IIT Bombay WSSE Pune Liveness Analysis: Live Variables Analysis 2/25 Defining Live Variables Analysis A variable v is live at a program point p, if some path from p to program exit contains an r-value oc- currence of v which is not preceded by an l-value occurrence of v. v is live at p v is not live at p v is live at p Start Start Start p p p v =a∗b v =a∗b a=v+2 v =a+2 vv==v +2 End End End Dec 2017 IIT Bombay WSSE Pune Liveness Analysis: Live Variables Analysis 2/25 Defining Live Variables Analysis A variable v is live at a program point p, if some path from p to program exit contains an r-value oc- Path based currence of v which is not preceded by an l-value specification occurrence of v. v is live at p v is not live at p v is live at p Start Start Start p p p v =a∗b v =a∗b a=v+2 v =a+2 vv==v +2 End End End Dec 2017 IIT Bombay WSSE Pune Liveness Analysis: Live Variables Analysis 3/25 Defining Data Flow Analysis for Live Variables Analysis INk = Genk ∪ (OUTk − Kill k) Genk , Kill k OUTk = INi ∪ INj INi INj Geni , Kill i Genj , Kill j OUTi OUTj Dec 2017 IIT Bombay WSSE Pune Liveness Analysis: Live Variables Analysis 3/25 Defining Data Flow Analysis for Live Variables Analysis Single statements or Maximal groups Basic Blocks ≡ of sequentially executed statements INk = Genk ∪ (OUTk − Kill k) Genk , Kill k OUTk = INi ∪ INj INi INj Geni , Kill i Genj , Kill j OUTi OUTj Dec 2017 IIT Bombay
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