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when running without the verifier, and I have not yet checked them to see if the new results are still correct. There are more verifier failures, but they all seem to be additional occurrences of verifier failures that occur with the existing PHIElimination pass. There are a few obvious issues with the code: 1) It doesn't properly update the register equivalence classes during copy insertion, and instead recomputes them before merging live intervals and renaming registers. I wanted to keep this first patch simple for debugging purposes, but it shouldn't be very hard to do this. 2) It doesn't mix the renaming and live interval merging with the copy insertion process, which leads to a lot of virtual register churn. Virtual registers and live intervals are created, only to later be merged into others. The code should be smarter and only create a new virtual register if there is no existing register in the same congruence class. 3) In one place the code uses a DenseMap per basic block, which is unnecessary heap allocation. There should be an inline storage version of DenseMap. I did a quick compile-time test of running llc on 403.gcc with and without StrongPHIElimination. It is slightly slower with StrongPHIElimination, because the small decrease in the coalescer runtime can't beat the increase in phi elimination runtime. Perhaps fixing the above performance issues will narrow the gap. I also haven't yet run any tests of the quality of the generated code. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122582 91177308-0d34-0410-b5e6-96231b3b80d8
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