[llvm-commits] [llvm] r85764 - in /llvm/trunk/lib/Target/ARM: ARM.td ARMBaseInstrInfo.cpp ARMBaseInstrInfo.h ARMInstrFormats.td ARMInstrInfo.cpp ARMInstrInfo.h Thumb1InstrInfo.cpp Thumb2InstrInfo.cpp

Anton Korobeynikov asl at math.spbu.ru
Sun Nov 1 23:04:41 PST 2009

Hello, Evan

> 1. When the register is virtual, it could have used
> machineregisterinfo to find the def. It would have been much faster.
Yes, however, I never saw such case in (rather huge) real codes. I will add it.

> 2. When the register is physical it can scan all the way to the top of
> the MBB, that's extremely expensive.
Do we have any better way? It seems - no. We need to find the def of the
register which is closest to the insertion point. Even if some instruction
numbering would be saved after RA, then iterating of instructions seems to
be cheaper than iterating over defs of the phys reg.

With best regards, Anton Korobeynikov
Faculty of Mathematics and Mechanics, Saint Petersburg State University

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