Optimizations provided by a compiler includes inlining small functions,code hoisting,dead store elimination,eliminating common subexpressions, loop unrolling, loop optimizations. A fragment of code that resides in the loop and computes the same value at each iteration is called a loop invariant code. Other optimizations may have to be triggered using explicit compiletime options. Data flow analysis flow graph, data flow equation, global optimization, redundant sub. Interval analysis, compiler loop optimization, algorithmic.
Identification of the 10% of the code is not possible for a compiler it is the job of a profiler. Cs3300 compiler design introduction to optimizations cseiitm. Code optimization during various phases i language features that produce poor code or inhibit various optimizations. Figure 2 shows an optimization known as loop unswitching. It becomes necessary to optimize the loops in order to save cpu cycles and memory. After generating intermediate code, the compiler can modify the intermediate code by address calculations and improving loops. Algorithms for two machineindependent optimizations. Ullman lecture37 dead code elimination, loop optimizations, code motion, induction variables and reduction in strength.
Compiler design cd notes pdf free download 2020 sw. The important loop optimizations are elimination of loop invariant computations and elimination of induction variables. Machineindependent optimizations 6 machineindependent optimization algorithms y. Loop speci c optimizations better performance because they alter the structure of the loop or make improvements that require many iterations to be e cient due to a large overhead. It plays an important role in improving cache performance and making effective use of parallel processing capabilities. Decreasing the number of instructions in an inner loop improves the running time of a program even if the amount of code outside that loop is increased.
I byname parameters i function that have side e ects, which may make code elimination or code movement impossible i alias creation, which can make redundant expression analysis very di cult i exceptions, which can cause unexpected and invisible jumps to handlers. The classic example of strength reduction converts strong multiplications inside a loop into weaker additions something that frequently occurs in array addressing. In this paper we present compiler optimizations with the aim of minimizing energy consumption of embedded applications. The second part, advanced topics, which includes the advanced chapters, covers the compilation of objectoriented and functional languages, garbage collection, loop optimizations, ssa form, loop scheduling, and optimization. A typical loop improvement is to move a computation that produces the same result each time around the loop to a point, in the program just before the loop is entered. Watch video lectures by visiting our youtube channel learnvidfun. Loops can be optimized by the following techniques. We will describe a loop optimization infrastructure based on improved induction variable, scalar. Compiler design 10 a compiler can broadly be divided into two phases based on the way they compile. Compiler design 9 loader loader is a part of operating system and is responsible for loading executable files into memory and execute them. The gcc optimization pipeline since 2017, members of the community have started adding some of the missing transformations to the compiler, e.
Optimization of basic blocks, loops in flow graph, introduction to global data flow analysis. Loop optimization is the most valuable machineindependent optimization because a programs inner loops are good candidates for improvement. Pdf loops in programs are the source of many optimizat ions for. Analysis phase known as the frontend of the compiler, the analysis phase of the compiler reads the source program, divides it into core parts, and then checks for lexical, grammar, and syntax errors. Krishna nandivada iit madras cs3300 aug 2019 25 30 example.
If we decrease the number of instructions in an inner loop then the running time of a program may be improved even if we increase the amount of code outside that loop. Introduction to machineindependent optimizations 1 nptel. We discuss loop optimization strategies and then, using directed test cases, analyze how gcc and clang use those techniques to optimize at di erent levels. In compiler theory, loop optimization is the process of increasing execution speed and reducing the overheads associated with loops. A program can have various constructs as basic blocks, like ifthenelse, switchcase conditional statements and loops such as dowhile, for, and. Download handwritten notes here get more notes and other study material of compiler design. For example, the memory architecture may provide better performance if two arrays are initialized in separate loops, rather than initializing both arrays. Ullman lecture38 optimization of basic blocks, loops in flow graph, introduction to global. Furthermore, unlike a traditional compiler, intended for desktop. Loop optimization is a machine independent optimization.
The loop independent code executes only once, instead of many times the loop might. Another important source of optimization concerns about increasing the speed of loops. This textbook is useful for computer science engineering cse. Loop optimizations contd induction variable elimination variables that are locked to the iteration of the loop. Although loop fusion reduces loop overhead, it does not always improve runtime performance, and may reduce runtime performance. In computing, an optimizing compiler is a compiler that tries to minimize or maximize some attributes of an executable computer program. Reduce code size achieved through code transformation while preserving semantics. Code optimization techniques in compiler design pdf gate. Compiler design frank pfenning lecture 17 october 22, 20 1 introduction optimizing loops is particularly important in compilation, since loops and in particular the inner loops account for much of the executions times of many programs. Optimization, on the other hand, still retains a sizable measure of mysticism.
Loop body optimizations procedure optimizations register allocation instruction scheduling control flow optimizations cache optimizations vectorization and parallelization advanced compiler design implementation. As you contemplate making manual changes, look carefully at which of these optimizations can be done by the compiler. Finally, in section 4, we survey the latest research papers in the eld of loop optimizations. Compiler optimization and code generation lecture 1 developed by. Code optimization and data flow analysis 09 periods code optimization consideration for optimization, scope of optimization, local optimization, loop optimization, frequency reduction, folding, dag representation. Generating code via macro expansion 2 code generation april, 2011. Nov 21, 2019 loop optimization is a machine independent optimization. Code optimization the stanford suif compiler group. This paper deals with the comparative study on various compiler optimization techniques. Threeaddress intermediate code each instruction is of the form x.
We illustrate our algorithm to synthesize weakest preconditions for compiler optimizations on a simple example. Cs3300 compiler design introduction to optimizations. Common requirements are to minimize a programs execution time, memory footprint, storage size, and power consumption the last three being popular for portable computers compiler optimization is generally implemented using a sequence of optimizing. Modular design supports multiple architectures list of supported backends latest stable release 6. This comprises loop optimizations for exploitation of simd instructions and.
Loop fusion is not commonly supported by c compilers. In frequency reduction, the amount of code in loop is decreased. Code motion, induction variable elimination, and reduction in strength. Pdf the new trends in compiler analysis and optimizations. Like other optimizations, loop optimizations are best applied to a control flow graph ir other opts may create opportunities for loop opts and vice versa, so it makes sense to alternate between them. Compilers often have to rewrite code to take maximal advantage of these design.
On the design of intermediate representations for loop nest optimization key. Loop tiling same as stripmining for nestedloops and convex shaped iteration space x loop collapsing two nested loops that refers to arrays be collapsed into single loop x loop coalescing same as loop collapsing but the loop limits do not match x loop unrolling duplicate the body of the loop multiple times and reduce the loop count. Loop optimization most programs run as a loop in the system. Puntambekar pdf free download for jntu books name of the book.
An induction variable is any variable whose value can be represented as a function of. To gain better understanding about code optimization techniques, watch this video lecture. Code optimization is the fifth phase in compiler design. Srikant department of computer science and automation indian institute of science bangalore 560 012 nptel course on principles of compiler design y. While advance compiler designs in computer architectural designs, there is a need to also employs data flow analysis among other improve on the code size, instruction execution methods, their mode of application is different speed, etc. Control flow optimization in loops using interval analysis. This textbook is useful for computer science engineering cse students belongs. The first part of the book, fundamentals of compilation, is suitable for a onesemester first course in compiler design.
The lexical analyzer reads the stream of characters making up the source program and groups the characters into meaningful sequences called lexemes. Loop optimization in compiler design geeksforgeeks. The tasks of the frontend scanning, parsing, semantic analysis are well understood and unoptimized code generation is relatively straightforward. Optimization is misnomer typically no guarantee transformations will improve performance, nor that compilation will produce optimal code this course. The class of loop optimizations which were considering in this post are centered on special variables called induction variables ivs. Data flow analysis flow graph, data flow equation, global optimization. Introduction to machineindependent optimizations 6. Frequency reduction code motion in frequency reduction, the amount of code in loop is decreased. Since tailrecursive functions are usually also turned into loops, the. Oct 23, 2019 induction variables loops are well known targets for optimization since they execute repeatedly and significant execution time is spent in loop bodies.
Optimizing compilers compiler structure optimization optimization. Loop optimization can be viewed as the application of a sequence of specific loop transformations listed below or in compiler transformations for highperformance computing to the source code or intermediate representation, with each transformation having an associated test for legality. On programming language design and implementation, pp. The moral of this story is that most often you should write code that is. Loop optimizations program hot spots often occur in loops especially inner loops not always. This paper will present a design for loop optimizations using highlevel loop transformations.
O2 more aggressive size and speed optimization o3 favor speed over size os like o2 but does not enable opt passed which increase size ofast o3 plus inaccurate math og optimize for debugging experience clang has oz which optimizes for size more aggressively disables loop vectorization. Like other optimizations, loop optimizations are best applied to a control flow graph ir other opts may create opportunities for loop opts and vice versa, so it makes sense to alternate between them loops may be hard to recognize at the cfg ir level many kinds of loops. Optimization is the field where most compiler research is done today. Can find pipelininglevel parallelism across loop iterations. Common requirements are to minimize a programs execution time, memory footprint, storage size, and power consumption the last three being popular for portable computers.
E liminating a few expensive operations inside an inner loop can speed your program more than days working on other parts. Chapters 12 19 historical origins of compiler optimization. Loop optimization loop optimization is most valuable machineindependent optimization because programs inner loop takes bulk to time of a programmer. But, many modern compilers emit the same object code for both, by use of clever techniques in particular, 2 this one is called loop induction variable elimination that work particularly well on idiomatic usage. Most execution time of a scientific program is spent on loops. Compilers often have to rewrite code to take maximal advantage of these designs. In this optimization, the compiler takes in the intermediate code and. Optimization via a sequence of loop transformations. Weakest precondition synthesis for compiler optimizations. Typically loop unrolling is performed as part of the normal compiler optimizations. What is code optimization what are advantages of code optimization. It calculates the size of a program instructions and data and. In compiler construction, strength reduction is a compiler optimization where expensive operations are replaced with equivalent but less expensive operations.
118 50 298 967 972 855 1611 1071 976 1167 352 890 1134 667 1082 592 1281 1660 1730 162 753 141 525 1709 1431 781 34 417 981 1287 1066 191 280