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The aim in this patch is to reduce work that VirtRegRewriter needs to do when telling MachineRegisterInfo which physregs are in use. Up until now VirtRegRewriter::rewrite has been doing rewriting and populating def info and then proceeding to set whether a physreg is used based this info for every physreg that the target provides. This can be expensive when a target has an unusually high number of supported physregs, and is a noticeable chunk of compile time for small programs on such targets. So to reduce compile time, this patch simply adds the use of a SparseSet to the rewrite function that is used to flag each physreg that is encountered in a MachineFunction. Afterward, rather than iterating over the set of all physregs for a given target to set the physregs used in MachineRegisterInfo, the new way is to iterate over the set of physregs that were actually encountered and set in the SparseSet. This improves compile time because the existing rewrite function was iterating over all MachineOperands already, and because the iterations afterward to setPhysRegUsed is reduced by use of the SparseSet data. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200919 91177308-0d34-0410-b5e6-96231b3b80d8
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