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...am implementing the following optimization for folding XOR instructions working on bits (it still must be extended to OR and AND instructions). Any comments and critics are appreciated. Basically, I try to identify a chain of XOR instructions and fold it. The below image illustrate this: [image: XORChain.png] In order to do that I am adding an additional function call to "visitXor()" in Instruction Combining. My Optimization function is attached as a patch file. (the diff was made using the 2.9 release version of llvm). Thanks Daniel Nicacio -------------- next part -------------- An...

2011/7/26 Daniel Nicácio <dnicacios at gmail.com>: > > I also would like to see why the "XOR  A,  -1" is not turned into a NOT, any > Probably because NOT (like NEG) doesn't exist :) <http://llvm.org/docs/LangRef.html#instref> I assume the decision was made that it wasn't worth adding the extra unary instructions when they can easily be handled in codegen

After a few more tests, I found out that if we set -unroll-threshold to a value large enough, and run "opt -std-compile-opts" or "opt -O3" 3 times, the unroll will be able to unroll the original loop 32 times, and when you have it unrolled for at least 32 times a optimization is triggered, folding it to a single "%xor.3.3.1 = xor i32 %tmp6, -1" (dont know why it does