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Re: unfused fma question


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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