Difference: CS255Spring09Discussions (2 vs. 3)

Revision 32009-02-22 - JohnPershing

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CS255/455 Spring 2009 Discussion Board

Last year's discussion page was a success for people to discuss and share the project experience, especially their experience with GCC. So this year, we are going to continue with the discussion tradition. This page is intended for anyone to post questions and everyone to answer them. Please insert questions at the beginning and separate each question with a horizontal rule separator. For other formatting instructions read the answer to this question.


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Q: I had several questions that Bin answered via e-mail. He asked me to summarize them here. It was never really detailed in class exactly what you do when you find a redundant statement. My initial thought was to simply replace the right hand side of a redundant statement with the left hand side of the statement which it was repeating. I then noticed that the success benchmark in this class how many statements we could remove from a program, and this method didn't remove any, it optimized the program by decreasing the number of operations executed, but didn't change the statement count. My next thought was that you needed to delete the statement and replace subsequent instances of the left hand side with what you would have replaced the right hand side with, but that has issues since we're only doing local value numbering, and deleting a statement could have wide spread effects in other basic blocks. So the question is what action should we take when we find a redundant statement?


 URCC problems

  • Insert Ast::Const nodes with the same numeric value will cause problem. Thus we have slightly changed the loop.c for Project Part 2. We will provide a solution soon.
 
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