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diff --git a/docs/HistoricalNotes/2001-06-01-GCCOptimizations.txt b/docs/HistoricalNotes/2001-06-01-GCCOptimizations.txt deleted file mode 100644 index 97af16a..0000000 --- a/docs/HistoricalNotes/2001-06-01-GCCOptimizations.txt +++ /dev/null @@ -1,63 +0,0 @@ -Date: Fri, 1 Jun 2001 16:38:17 -0500 (CDT) -From: Chris Lattner <sabre@nondot.org> -To: Vikram S. Adve <vadve@cs.uiuc.edu> -Subject: Interesting: GCC passes - - -Take a look at this document (which describes the order of optimizations -that GCC performs): - -http://gcc.gnu.org/onlinedocs/gcc_17.html - -The rundown is that after RTL generation, the following happens: - -1 . [t] jump optimization (jumps to jumps, etc) -2 . [t] Delete unreachable code -3 . Compute live ranges for CSE -4 . [t] Jump threading (jumps to jumps with identical or inverse conditions) -5 . [t] CSE -6 . *** Conversion to SSA -7 . [t] SSA Based DCE -8 . *** Conversion to LLVM -9 . UnSSA -10. GCSE -11. LICM -12. Strength Reduction -13. Loop unrolling -14. [t] CSE -15. [t] DCE -16. Instruction combination, register movement, scheduling... etc. - -I've marked optimizations with a [t] to indicate things that I believe to -be relatively trivial to implement in LLVM itself. The time consuming -things to reimplement would be SSA based PRE, Strength reduction & loop -unrolling... these would be the major things we would miss out on if we -did LLVM creation from tree code [inlining and other high level -optimizations are done on the tree representation]. - -Given the lack of "strong" optimizations that would take a long time to -reimplement, I am leaning a bit more towards creating LLVM from the tree -code. Especially given that SGI has GPL'd their compiler, including many -SSA based optimizations that could be adapted (besides the fact that their -code looks MUCH nicer than GCC :) - -Even if we choose to do LLVM code emission from RTL, we will almost -certainly want to move LLVM emission from step 8 down until at least CSE -has been rerun... which causes me to wonder if the SSA generation code -will still work (due to global variable dependencies and stuff). I assume -that it can be made to work, but might be a little more involved than we -would like. - -I'm continuing to look at the Tree -> RTL code. It is pretty gross -because they do some of the translation a statement at a time, and some -of it a function at a time... I'm not quite clear why and how the -distinction is drawn, but it does not appear that there is a wonderful -place to attach extra info. - -Anyways, I'm proceeding with the RTL -> LLVM conversion phase for now. We -can talk about this more on Monday. - -Wouldn't it be nice if there were a obvious decision to be made? :) - --Chris - |