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on every node as it legalizes them. This makes it easier to use hasOneUse() heuristics, since unneeded nodes can be removed from the DAG earlier. Make LegalizeOps visit the DAG in an operands-last order. It previously used operands-first, because LegalizeTypes has to go operands-first, and LegalizeTypes used to be part of LegalizeOps, but they're now split. The operands-last order is more natural for several legalization tasks. For example, it allows lowering code for nodes with floating-point or vector constants to see those constants directly instead of seeing the lowered form (often constant-pool loads). This makes some things somewhat more complicated today, though it ought to allow things to be simpler in the future. It also fixes some bugs exposed by Legalizing using RAUW aggressively. Remove the part of LegalizeOps that attempted to patch up invalid chain operands on libcalls generated by LegalizeTypes, since it doesn't work with the new LegalizeOps traversal order. Instead, define what LegalizeTypes is doing to be correct, and transfer the responsibility of keeping calls from having overlapping calling sequences into the scheduler. Teach the scheduler to model callseq_begin/end pairs as having a physical register definition/use to prevent calls from having overlapping calling sequences. This is also somewhat complicated, though there are ways it might be simplified in the future. This addresses rdar://9816668, rdar://10043614, rdar://8434668, and others. Please direct high-level questions about this patch to management. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143177 91177308-0d34-0410-b5e6-96231b3b80d8
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