condition flags USE in AD instruct

Christian Thalinger Christian.Thalinger at Sun.COM
Tue Apr 14 13:34:26 PDT 2009

On Tue, 2009-04-14 at 12:42 -0700, Tom Rodriguez wrote:
> Matching Bools and Cmps is kind of special.  All Ifs start out looking  
> like (If (Bool (Cmp)) but before matching they are converted to (If  
> (Bool (Cmp)) (Cmp)) so that they Bool and Cmp can be matched  
> together.  The reason for this is that C2 separates the comparison  
> operation from the interpretation of those results.  

I see, thanks.

> I don't know the  
> full history of this but I assume it's to encourage GVN on the  
> compares which collects together code that compares the same values  
> but asks different questions about them.  So if you want to use the  
> result of a compare in an AddcI I think you need to use that same  
> logic.  In particular you need to modify Matcher::find_shared to do  
> some variation of the Alt_Post_Visit logic on your AddcI to add an  
> input for the Cmp and shove it into a BinaryNode so you can match  
> using (Set dst (AddcI (Binary cop cr) (Binary dst src))).

I already did something like that, but I only add one BinaryNode.  I
will add the second one and see if it works.

-- Christian

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