This patch adds support to continuously CSE instructions during each of the GISel passes. It consists of a GISelCSEInfo analysis pass that can be used by the CSEMIRBuilder.
This patch also includes some changes to MachineIRBuilderBase (which is separated out here - https://reviews.llvm.org/D52131). I have enabled it in the legalizer for now. I've also only updated AArch64 for the API and test changes - I'll update the rest post feedback.
I measured some off tree benchmarks for compile time and I didn't notice too much of a compile time regression (<1%). I'll try to get some numbers for AArch64 with llvm-test-suite.
Looking forward to your feedback.