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Re: [PATCH] PR63404, gcc 5 miscompiles linux block layer


On 10/10/14 10:52, Richard Henderson wrote:

I missed that message.  Interesting.

I wonder what kind of fallout there would be from changing LO_SUM to
RTX_BIN_ARITH, which is what it should have been all along.

My guess is that someone looked at HIGH being RTX_CONST_OBJ and thought that
LO_SUM should also be a kind of object too.
Most likely. One could even make an argument that LO_SUM should be a constant, but that's a more intrusive change.



 But it's really a lot more like a
kind of PLUS.  If instead we had a LOW to match HIGH it would have been
Right. In fact, I believe at the hardware level it's typically implemented as addition.

Jeff


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