{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Lecture6 - Type-safety and Compilers CSE 501 Lecture 6 1...

Info icon This preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
Type-safety and Compilers CSE 501 Lecture 6 April 20, 2009 1
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Preliminaries Critiques? A Verifiable SSA Program Representation for Aggressive Compiler Optimization Fault-safe Code Motion for Type-safe Languages Questions on HW 1? HW 2 will be posted later today 2
Image of page 2
Type safety A property of a programming language: a language is type-safe if it guarantees the integrity of its data types: An int is a really an int. A String is really a String. A char[] is really a char[]. Implies memory safety 3
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Type-safe languages Unsafe languages: C, C++, ... Pointer arithmetic, casting, manual deallocation can generate pointers to invalid memory. Safe languages: Java, C#, Python, JavaScript, ML, ... Static checks: Deref. of an int won’t compile Dynamic checks: Null check on a field access Automatic garbage collection 4
Image of page 4
Example Java source if (a != null) while (!done) { b = (B) a; ... = ... b.x ...; ... } Java developer - compiles to bytecode - ships to client Client - verifies bytecode - compile to native code - executes Bytecode (simplified) ifnull a goto EXIT L: ifeq done, 0 goto EXIT b = checkcast a, B t1 = getfield b, B::x ... goto L EXIT: Verifiably type-safe - checkcast : - runtime type check - getfield : - statically typed - runtime null check 5
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Why type-safety? Security, reliability, debuggability Buffer overflows, etc., common exploits Untrusted code, e.g., in web browsers No seg faults or mysterious corruption Is our C subset type-safe? 6
Image of page 6
How does type safety impact compilation? For performance, optimizing compiler must: Eliminate null / type / bounds checks when possible Preserve the safety guarantees of the language - cannot just elide all checks!
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern