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cea8688ee4
when possible, avoiding the load (and avoiding the copy if the value is already in the right register). This patch came about when I noticed code like the following being generated: store R17 -> [SS1] ...blah... R4 = load [SS1] This was causing an LSU reject on the G5. This problem was due to the register allocator folding spill code into a reg-reg copy (producing the load), which prevented the spiller from being able to rewrite the load into a copy, despite the fact that the value was already available in a register. In the case above, we now rip out the R4 load and replace it with a R4 = R17 copy. This speeds up several programs on X86 (which spills a lot :) ), e.g. smg2k from 22.39->20.60s, povray from 12.93->12.66s, 168.wupwise from 68.54->53.83s (!), 197.parser from 7.33->6.62s (!), etc. This may have a larger impact in some cases on the G5 (by avoiding LSU rejects), though it probably won't trigger as often (less spilling in general). Targets that implement folding of loads/stores into copies should implement the isLoadFromStackSlot hook to get this. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23388 91177308-0d34-0410-b5e6-96231b3b80d8
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