a-original.ll contains the basic, unpotimized code.
Run :
$ opt -S -wanted_pass a-original.ll -o output.ll
Differents passes are for example :
- instcombine : combines the instructions
- deadargelim : gets rid of the dead argument
- loweratomic : lowers atomic intrinsics to non-atomic form
- mem2reg : promotes memoty to register
- memcpyopt : MemCpy optimization
- ...
One can write a specific pass. Here is the list of all available pass for LLVM.