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030f090aee
Before register allocation, instructions can be moved across calls in order to reduce register pressure. After register allocation, we don't gain a lot by moving callee-saved defs across calls. In fact, since the scheduler doesn't have a good idea how registers are used in the callee, it can't really make good scheduling decisions. This changes the schedule in two ways: 1. Latencies to call uses and defs are no longer accounted for, causing some random shuffling around calls. This isn't really a problem since those uses and defs are inaccurate proxies for what happens inside the callee. They don't represent registers used by the call instruction itself. 2. Instructions are no longer moved across calls. This didn't happen very often, and the scheduling decision was made on dubious information anyway. As with any scheduling change, benchmark numbers shift around a bit, but there is no positive or negative trend from this change. This makes the post-ra scheduler 5% faster for ARM targets. The secret motivation for this patch is the introduction of register mask operands representing call clobbers. The most efficient way of handling regmasks in ScheduleDAGInstrs is to model them as barriers for physreg live ranges, but not for virtreg live ranges. That's fine pre-ra, but post-ra it would have the same effect as this patch. llvm-svn: 151265 |
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