Basic Block & CFG PQ - 1

Duration: 24 min

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Inside: a video lesson and guided study material.

Module outline

  1. About Course: UPPSC Course Overview
  2. Interview Preparation & Guidance: Interview Preparation
  3. Paper 1 | General Hindi: भाषा, लिपि, ध्वनि, वर्ण, अक्षर, स्वर, व्यंजन, मात्रा और संयुक्ताक्षर, वर्तनी, वर्ण-विन्यास, अनुस्वार, अनुनासिक, चंद्रबिंदु और ‘र’ के रूप, शब्द, पद और शब्द-भेद, संज्ञा और सर्वनाम, विशेषण और क्रिया, लिंग, वचन, पुरुष और कारक, काल, वाच्य, वाक्य और वाक्य-भेद, वर्णमाला, समास, संधि, Multi-Topic Content (Cross-Concept Material), हिन्दी की ध्वनि और स्वनिम व्यवस्था, प्राचीन और मध्यकालीन भारतीय आर्यभाषाएँ, काव्य के लक्षण, हेतु और प्रयोजन, हिन्दी की रूप रचना, हिन्दी शब्द रचना, हिन्दी साहित्येतिहास दर्शन, भक्तिकालीन काव्यधाराएँ, भारतीय काव्यशास्त्र की परंपरा, भारतीय नवजागरण और स्वाधीनता आंदोलन, अन्य गद्य विधाएँ एवं प्रवासी साहित्य, निर्धारित उपन्यासों का तुलनात्मक अध्ययन, गोदान, हिन्दी कहानी का विकास, स्वातंत्र्योत्तर और नयी कहानी, हिन्दी निबंध का विकास, शुक्लोत्तर निबंध, द्विवेदी और शुक्ल युग के निबंध, हिन्दी की संवैधानिक स्थिति, आधुनिक भारतीय आर्यभाषाएँ और हिन्दी का उद्भव, हिन्दी भाषा प्रयोग के विविध रूप, रीतिकाल, जीवनी, द्विवेदी युग और छायावाद, रीति, वक्रोक्ति और औचित्य सिद्धान्त, शब्दशक्ति और ध्वनि सिद्धान्त, रस सिद्धान्त और साधारणीकरण, उत्तर आधुनिकतावाद, लोहिया दर्शन, हिन्दी उपन्यास का विकास, हिन्दी नवजागरण, अंबेडकर दर्शन, आदिकाल, प्रयोगवाद और नयी कविता, छायावादी काव्य: प्रसाद और निराला, प्रगतिवाद से समकालीन कविता, निर्गुण भक्ति काव्य, द्विवेदीयुगीन काव्य, रीतिकालीन काव्य, आरंभिक हिन्दी उपन्यास, स्वातंत्र्योत्तर उपन्यास, आत्मकथा, स्वाधीनता-पूर्व प्रेमचंदोत्तर उपन्यास, निर्धारित कहानियों का तुलनात्मक अध्ययन, साठोत्तरी नाटक, प्रसाद और प्रसादोत्तर युग के नाटक, भारतेन्दु युगीन नाटक, स्वातंत्र्योत्तर नाटक, भारतेन्दु युगीन निबंध, संस्मरण और रेखाचित्र, व्यंग्य, एक साहित्यिक की डायरी, संस्कृति के चार अध्याय, सगुण भक्ति काव्य, हिन्दी नाटक, एकांकी और रंगमंच, आधुनिक गद्य और हिन्दी नवजागरण, अलंकार सिद्धान्त, हिन्दी आलोचना का विकास, भक्ति आंदोलन, कल्पना, बिम्ब, प्रतीक, मिथक और फंतासी, नयी कविता का विस्तार और साठोत्तरी कविता, उत्तर-छायावादी और प्रगतिवादी काव्य, काव्यगुण और काव्यदोष, प्लेटो, अरस्तू और पाश्चात्य परंपरा, मार्क्सवाद, स्वच्छन्दतावादी काव्यशास्त्र, आधुनिक पाश्चात्य आलोचना, भाषा और भाषा परिवार, देवनागरी लिपि
  4. Paper 2 | General Studies: State Wise GK, Polity, Geography, History, GK- Current Affairs
  5. Paper 1 | Programming Language: Language Design, C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling, OOPS with C++
  6. Paper 1 | Database Management Systems: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, File Organization & Indexing, Relational Algebra, SQL, Relational Calculus, Transaction Management, Concurrency Control, ORDBMS, NoSQL
  7. Paper 1 | Cyber Security: Society, Law & Ethics, Cyber Threats and Malware Attacks, Role of Internet and Web Services, Security in Mobile and Wireless Computing, Electronic Data Interchange and E-Commerce, Physical Security and Cryptography Basics, Intrusion Detection Systems (IDS), Cyber Safety and Security, Ethical Hacking, कंप्यूटर की मूल बातें और हार्डवेयर / Computer Fundamentals and Hardware, प्रत्यक्ष बोध / Literal Comprehension, कंप्यूटर सॉफ्टवेयर / Computer Software, निष्कर्षात्मक बोध / Inferential Comprehension, आलोचनात्मक बोध / Critical Comprehension, इंटरनेट और वर्ल्ड वाइड वेब / Internet and World Wide Web, ई-मेल और ऑनलाइन संचार / Email and Online Communication, साइबर सुरक्षा / Cyber Security, अपशिष्ट प्रबंधन / Waste Management, डिजिटल नैतिकता, बौद्धिक संपदा और समाज / Digital Ethics, IPR and Society, डिजिटल एवं नव माध्यम / Digital and New Media, क्लाउड और वितरित कंप्यूटिंग / Cloud and Distributed Computing, शोध नैतिकता / Research Ethics, उभरती प्रौद्योगिकियाँ / Emerging Technologies, शिक्षा और शासन में ICT / ICT in Education and Governance
  8. Paper 1 | Computer Organization and Architecture: Basics of COA, Programming the Basic Computer, Cache Memory Organization, Input Output Organisation, Instr Formats & Modes, Register Transfer and Microoperations, Control Unit Design
  9. Paper 1 | Computer Networks: Introduction to CN, Data Communication, DLL: Access Control, DLL: Flow Control, DLL: Error Control, DLL: Framing, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Net Layer:Routing Protocol, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware basics, Network Security
  10. Paper 1 | Design and Analysis of Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos, Advanced Algorithms
  11. Paper 1 | Data Structures: Introduction to DS, Array, Linked List, Stack, Queue, Tree, Graphs, Hashing
  12. Paper 1 | Discrete Structures and Theory of Logic: क्रमचय, संचय एवं प्रायिकता / Permutation, Combination and Probability, Set Theory, Relations, Functions, Propositional and Predicate Logic, Graph Theory, Group Theory
  13. Paper 1 | Software Project Management: Software Project Management
  14. Paper 2 | Operating Systems: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, Disc Scheduling, File Management, Unix OS, Linux OS, Security
  15. Paper 2 | Compiler Design: Intro to Compilers, Lexical Analysis, Grammar & CFG, Syntax Analysis: Top-Down, Syntax Analysis: Bottom-Up, Semantic Analysis & SDT, Intermediate Code Gen, Code Optimization, Run Time Environment, Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Pushdown Automata & CFG, Complexity Theory
  16. Paper 2 | Artificial Intelligence & High Performance Computing: Approaches to AI, Search Algorithms, Game Playing, Knowledge Representation, Planning, Multi Agent Systems, Natural Language Processing, Emerging Tech Trends
  17. Paper 2 | Image Processing: Digital Image Fundamentals, Image Enhancement, Image Restoration, Color Image Processing, Image Compression
  18. Paper 2 | Software Engineering: Fundamentals of Software Engineering, Software Requirements and Quality Assurance, Software Design, Estimation and Metrics, Software Testing, Software Maintenance and Configuration Management
  19. Paper 2 | Computer Graphics: Basics of Computer Graphics, 2-D Geometrical Transforms and Viewing, 3-D Object Representation, Geometric Transformations and Viewing
  20. Paper 2 | Web Technologies: Website, Browser & Services, Internet Fundamentals, Web Design & Development, Protocols & Services, Web Publishing & Hosting, Server Side & Security, Emerging Technologies, HTML Basics, JavaScript-Basics, Java
  21. Paper 2 | Soft Computing: Fuzzy Sets, Artificial Neural Networks, Genetic Algorithms
  22. Paper 2 | Distributed System: Distributed Systems
  23. UPPSC Live Class Recordings: UPPSC Polytechnic Lecturer 2025 (CS)
  24. Previous Year Papers:
  25. Mock Test:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This lecture provides a comprehensive tutorial on constructing Control Flow Graphs (CFG) from three-address code, focusing on the identification of leaders and the division of code into basic blocks. The instructor systematically demonstrates how to locate leaders—specific instructions that begin a new block, such as the first statement of the program, any target of a conditional or unconditional jump, and the instruction immediately following a jump. Through multiple worked examples involving arithmetic operations, conditional checks like 'if d > 0 goto', and unconditional jumps, the instructor illustrates how to group sequential instructions into rectangular nodes labeled B1, B2, etc. The session transitions from identifying leaders to drawing the CFG by connecting these blocks with directed edges that represent the flow of control, explicitly labeling branches for 'True' and 'False' outcomes of conditional statements. The visual progression moves from raw code analysis to the final graphical representation, emphasizing the structural relationship between linear code segments and their execution paths.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The lecture begins with the instructor presenting a three-address code problem on screen, asking students to identify leaders and divide the sequence into basic blocks. Visible text displays a problem statement: 'Q. Consider the three-address code:' followed by lines such as '1. a = b + c' and '3. if d > 0 goto 7'. The instructor points to specific lines, notably line 3 containing a conditional jump, and writes 'Leaders: 1' on the screen to initiate the identification process. This initial phase establishes the foundational rule that the first statement of any code sequence is always a leader, setting the stage for subsequent analysis of jump targets.

  2. 2:00 – 5:00 02:00-05:00

    The instructor continues solving the problem by circling 'goto' statements to identify potential leaders within the code sequence. He lists the identified leader line numbers as 1, 3, 7, and 8 on the screen. The instructor then begins drawing a box to represent the first basic block, labeled B1, which contains lines 1, 2, and 3. He proceeds to identify subsequent leaders for blocks B2 and B3, writing the corresponding statement numbers into rectangular boxes representing each block. This section demonstrates the grouping of sequential instructions between leaders into single blocks, visually separating them to prepare for graph construction.

  3. 5:00 – 10:00 05:00-10:00

    The instructor analyzes a sample problem with labels B1, B2, etc., identifying leaders at lines 1, 7, 8, and 4. He then moves to a new example starting with 'goto 5' and identifies leaders as 1, 5, and 2. The visible text shows code snippets like '1. a=b+c' and '3. if d>0 goto 6'. The instructor emphasizes the rules for identifying leaders in control flow graphs, focusing on jump targets and first statements. This segment reinforces the methodology of scanning code for unconditional jumps and conditional branches to determine where new basic blocks must begin, ensuring all execution paths are accounted for in the block division.

  4. 10:00 – 15:00 10:00-15:00

    The instructor constructs a Control Flow Graph (CFG) based on the previously identified basic blocks. He starts by drawing an arrow from a 'Start' node to block B1, which contains the instruction 'goto 5'. He then draws an arrow from B1 to block B3, which contains the instruction 'print(a)', indicating a fall-through or sequential flow. Finally, he begins to draw block B2 to the right of B3. The on-screen text lists instructions like '1. goto 5' and '5. print(a)'. This phase transitions from code analysis to visual mapping, showing how basic blocks are connected by directed edges that represent the flow of control between different sections of the program.

  5. 15:00 – 20:00 15:00-20:00

    The instructor explains the construction of a Control Flow Graph (CFG) from a sequence of basic blocks, demonstrating how to handle conditional jumps ('if' statements) and unconditional jumps ('goto') by drawing branches labeled 'True' and 'False'. The process involves mapping code lines to nodes (B1, B2, etc.) and connecting them based on the flow of execution. Visible text includes '1. a = b + c' and '2. if 10 > 20 goto 5'. The instructor draws a CFG structure with nodes B1, B2, B3 and labels the branching logic for conditional statements. This section highlights the critical step of visualizing jump targets in a control flow diagram, ensuring that both the success and failure paths of conditional logic are explicitly represented.

  6. 20:00 – 24:18 20:00-24:18

    The instructor concludes by explaining the construction of a Control Flow Graph (CFG) from three-address code, identifying leaders in the code sequence and grouping them into basic blocks B1, B2, B3, and B4. He draws the CFG nodes and edges to visualize the flow of execution based on conditional jumps like 'if 10 > 20 goto 5'. The visible text lists leaders as 'Leaders: 1, 5, 7' and shows code lines such as '4. goto 7'. The instructor analyzes the final graph, counting nodes and edges to verify the structure. This final segment reinforces the complete workflow from leader identification to graph construction, emphasizing the relationship between code structure and control flow visualization.

The lecture systematically guides students through the process of converting three-address code into a Control Flow Graph. The core methodology involves identifying leaders, which are specific instructions that mark the beginning of a new basic block. These include the first statement of the program, any target of a jump instruction (conditional or unconditional), and the instruction immediately following a jump. Once leaders are identified, sequential instructions between them are grouped into basic blocks, typically denoted as B1, B2, etc. The instructor uses multiple examples to illustrate this, ranging from simple arithmetic sequences to those containing conditional logic like 'if d > 0 goto'. The visual representation involves drawing rectangular nodes for each block and connecting them with directed edges. Crucially, conditional jumps are handled by creating two outgoing edges from the block containing the condition: one labeled 'True' pointing to the jump target, and another labeled 'False' pointing to the next sequential block. Unconditional jumps create a single edge from the current block to the target block. The final output is a graph that accurately reflects all possible execution paths within the code, providing a clear structural overview for compiler optimization and analysis.

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