Lecture 1 CS 380C 1

380C

Last Time– Course

organization– Read Backus et al.

Announcements– Hadi lab Q&A Wed

1-2 in Painter 5.38N

– UT Texas Learning Center: 5 hours of free writing consultation, $13per hour

Today– Questions on

course organization?

– What’s a compiler?

– How does it work?

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What is a compiler?

• A program that translates a program in one language to another language– The essential interface between applications &

architectures• Typically lowers the level of abstraction

– analyzes and reasons about the program & architecture

• We expect the program to be optimized, i.e., better than the original– ideally exploiting architectural strengths and

hiding weaknesses

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When should we compile?

Ahead-of-time: before you run the program

Offline profiling: compile several times compile/run/profile.... then run again

Just-in-time: while you run the program required for dynamic class loading, i.e., Java, Python, etc.

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Aren’t compilers a solved problem?

“Optimization for scalar machines is a problem that was solved ten years ago.”

David Kuck, Fall 1990

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Aren’t compilers a solved problem?

“Optimization for scalar machines is a problem that was solved ten years ago.”

David Kuck, Fall 1990

• Architectures keep changing• Languages keep changing• Applications keep changing - SPEC CPU? • When to compile keeps changing

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Role of compilers

Bridge complexity and evolution in architecture, languages, & applications

Help programmers with correctness, reliability, program understanding

Compiler optimizations can significantly improve performance – 1 to 10x on conventional processors

Performance stability: one line change can dramatically alter performance– unfortunate, but true

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Optimization

What should it do?

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Optimization

What should it do?1. improve running time, or2. decrease space requirements3. decrease power consumption

How does it do it?

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Analysis

Scope of program analysis1. within a basic block (local)2. within a method (global)3. across methods (interprocedural)

Analysis1. control flow graph - dominators, loops, etc.2. dataflow analysis - flow of values3. static-single-assignment – transform

programs such that each variable has a unique definition

4. alias analysis - pointer memory usage5. dependence analysis - array memory

usage

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Example optimizations

Division of optimizations1. Machine independent2. Machine dependent

Faster code optimizations– common subexpression elimination– constant folding – dead code elimination– register allocation – scheduling – loop transformations

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Basic Compiler Structure

Program Machinecode

Higher to lower level representations, analyses, & transformations

Structural inlining

unrollingloop perm

Scalar cse

constantsexpressions

Memory scalar repl

ptrs

Reg. Alloc

Scheduling peephole

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Exciting times

New and changing architectures Hitting the microprocessor wall multicore, tiled architectures, tiled memory systems

Object-oriented languages becoming dominant paradigm Java and C# coming to your OS soon - Jnode, Singularity Security and reliability, ease of programming

Key challenges and approaches Latency & parallelism still key to performance Language & runtime implementation efficiency Orchestrating a new software/hardware dance Break down artificial system boundaries

CompilerProgrammer RuntimeCode Code

Specification Future behavior

Feedback H/S Profiling

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Questions?

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Programming Assignment #1

• 380C Lab 1• Due: Friday 9/11 5pm• Translate from 3 address code to C

– We provide a high-level language: • SC: a C-Subset that has functions, recursion, one type

of integer (long==8 bytes), arrays, structs, no floating point, no pointers, etc.

– We provide “csc” a C-subset compiler that translates from SC to valid 3 address code

– You translate it back to C code

• Hadi will be available for Q&A Wednesday 9/2 1-2pm (special location).

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Overview

Today– Introduction to

compilers

Next Time– program

representation – control flow– Read wiki--No

critique on wiki reading!