[llvm] r207301 - [X86] Implement TargetLowering::getScalingFactorCost hook.

[Krzysztof Parzyszek]

On 4/26/2014 5:15 PM, Chandler Carruth wrote:
>
> The problem I hit was the *DAG* destroying the information because it is
> represented as arbitrary math in the DAG and we have a bunch of DAG
> combines for math. If you want to make the problem I observed better,
> the way to do so is to introduce an addressing mode DAG node (or kill
> off the DAG completely).

What would be nice is if the DAG combiner consulted the targets whether 
to perform any given operation or not.  This type of problem extends 
beyond addressing modes.  Even for a specific target, a specific 
transformation may be beneficial or deterimental depending on 
circumstances.  Currently, the target-specific combining only happens 
when the generic one (visit) does nothing.

-K

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