unfused fma question

Marc Glisse marc.glisse@inria.fr
Mon Feb 23 18:59:00 GMT 2015


On Mon, 23 Feb 2015, Jeff Law wrote:

> On 02/23/15 11:38, Joseph Myers wrote:
>> 
>> (I wonder if convert_mult_to_fma is something that should move to
>> match-and-simplify infrastructure.)
> Yea, it probably should.

Currently, it happens in a pass that is quite late. If it moves to 
match-and-simplify, I am afraid it might inhibit some other optimizations 
(we can turn plus+mult to fma but not the reverse), unless we use some way 
to inhibit some patterns until a certain pass (possibly a simple "if", if 
that's not too costly). Such "time-restricted" patterns might be useful 
for other purposes: don't introduce complicated vector/complex operations 
after the corresponding lowering passes, do narrowing until a certain 
point but then prefer fast integer sizes, etc (I haven't thought about 
those particular examples, they are only an illustration).

-- 
Marc Glisse



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