Introduction to Advanced Topics Chapter 1 Text Book: Advanced compiler Design implementation By Steven S Muchnick (Elsevier)

Outline Review of compiler structure Advanced issues in elementary topics The importance of optimizations Structure of optimizing compilers Placement of optimizations Advanced topics

Compiler Structure String of characters Scanner tokens Parser Symbol table and access routines AST OS Interface Semantic analyzer IR Code Generator Object code

Advanced Issues in Elementary Topics Symbol table management(3) Efficiency Overloading Type Inference Intermediate Language Selection(4) Run-Time Support(5) Producing Code Generators (6)

Intermediate Language Selection Low Vs. High level control flow structures Flat Vs. Hierarchical (tree) Machine Vs. High level of instructions (Symbolic) Registers Vs. Stack Normal forms (SSA) Intermediate forms: Control Flow Graph, Call Graph, Program Dependence Graph Issues: Engineering, efficiency, portability, optimization level

IRs in the Book LIR MIR s2 s1 v v1 HIR s4  s3 t2  v2 L1: if s2 >s6 goto L2 s7  addr a s8  4*s9 s10  s7+s8 [s10]  2 s2  s2 + s4 goto L1 L2: MIR v v1 t2  v2 t3  v3 L1: if v >t3 goto L2 t4  addr a t5  4*i t6  t4+t5 *t6  2 v  v + t2 goto L1 L2: HIR for v v1 by v2 to v3 do a[i] :=2 endfor

Advanced Issues in Elementary Topics Symbol table management(3) Efficiency Overloading Type Inference Intermediate Language Selection(4) Run-Time Support(5) Producing Code Generators (6)

Run-Time Support Data representation and instructions Register usage Stack frames (activation records) Parameter passing disciplines Symbolic language support Garbage Collection

Advanced Issues in Elementary Topics Symbol table management(3) Efficiency Overloading Type Inference Intermediate Language Selection(4) Run-Time Support(5) Producing Code Generators (6)

The Importance of Optimizations One pass compilers produce slow code Much of the time spent in loops optimize loops Machines can be simpler and faster if optimizing compilers are used (RISC, VLIW) Programs are complex and general Compilers need to be modular

SPARC code C code ldw a, r1 ldw b, r2 add r1, r2, r3 Optimized stw r3, c ldw c, r3 add r3, 1, r4 stw r4, d Optimized SPARC code add r1, r2, r3 add r3, 1, r4 C code int a, b, c, d; c = a + b; d = c + 1; 2 cycles 10 cycles

Application Dependent Optimizations Functional programs replacement of recursion by loops (tail-calls elimination) replacement of heap by stack Object Oriented Programs Dead member elimination Replacement of virtual by static function Numeric Code Database Code

IR generator String Object Scanner Parser Semantic LIR generator Optimizer Fin. assembly Tokens AST LIR Object String Scanner Parser Semantic IR generator Optimizer Code generator Tokens AST MIR LIR Post. optimizer

Mixed vs. Low Level Optimizers Sun-SPARC, Dec. Alpha, SGI-MIPS, Intel’s 386 Easier to port More efficient compilation? Supports CISC Low Level HP-PA-RISC/IBM-Power PC More efficient code Conceptually simpler (in RISC) Used for multiple programming languages

Translation by Preprocessing Some programming languages are translated into C Elimination of includes, C++(cfront), Haskel Quick and portable solution C supports some indirect source level debugging Other examples: Fortran into “vector” Fortran program

Data-Cache Optimizations(20) String Scanner Tokens Parser AST Semantic HIR Data-cache optimizer MIR  Object

IBM PowerPC compiler String Scanner Tokens Parser AST Semantic Object Scanner Parser Semantic LIR generator Optimizer Fin. assembly Tokens AST LIR=XIL LIR Data-cache optimizer Low-to-High High-to-Low HIR=YIL

Outline Review of compiler structure Advanced issues in elementary topics The importance of optimizations Structure of optimizing compilers Placement of optimizations Advanced Topics

Scalar replacement of array references Data-cache optimizations Procedure integration Tail-call elimination Scalar replacement of aggregates Sparse constant propagation Interprocedural constant propagation Procedure specialization and cloning Sparse conditional constant propagation Inline expansion Leaf-routine optimizations Instruction Scheduling 1 Register allocation Instruction Scheduling 2 Intraprocedural I-cache optimizations Instruction prefetching Data prefertching Branch predication Global value numbering Local and global copy propagation Sparse conditional constant propagation Dead code elimination Common Subexpression Elimination Loop invariant code motion Interprocedural register allocation Interprocedural I-cache optimization Partial redundency Elimination