[llvm-commits] [llvm] r51660 - in /llvm/trunk: include/llvm/Target/TargetInstrDesc.h lib/CodeGen/MachineInstr.cpp lib/Target/Target.td utils/TableGen/CodeGenInstruction.cpp utils/TableGen/CodeGenInstruction.h utils/TableGen/InstrInfoEmitter.cpp

[Evan Cheng]

Why do we want another flag? In two-address pass, we want to remat the  
def instead of copying its value if the instruction is *cheap*.

Most of the rematerializable instructions are cheap. But I don't think  
we want to remat load from constantpool here, do we?

In the long run, we want proper cost information for every instruction  
instead of Rematerializable and / or CheapAsMove. Then we can replace  
the whole mess with proper checks. Until then, I don't see something  
like CheapAsAMove buys us.

Evan

On May 28, 2008, at 4:56 PM, Chris Lattner wrote:

>
> On May 28, 2008, at 4:50 PM, Evan Cheng wrote:
>
>> Please don't add another flag. For now, please check if an  
>> instruction
>> is rematerializable && !mayload.
>
> Why?
>
> -Chris
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