This is the mail archive of the
mailing list for the GCC project.
Re: unfused fma question
- From: Marc Glisse <marc dot glisse at inria dot fr>
- To: Jeff Law <law at redhat dot com>
- Cc: Joseph Myers <joseph at codesourcery dot com>, Steve Ellcey <sellcey at imgtec dot com>, gcc at gcc dot gnu dot org
- Date: Mon, 23 Feb 2015 19:59:02 +0100 (CET)
- Subject: Re: unfused fma question
- Authentication-results: sourceware.org; auth=none
- References: <02d0fee7-2c86-4291-8405-ae250d3210d9 at BAMAIL02 dot ba dot imgtec dot org> <alpine dot DEB dot 2 dot 10 dot 1502231833070 dot 7064 at digraph dot polyomino dot org dot uk> <54EB73FD dot 1000003 at redhat dot com>
- Reply-to: gcc at gcc dot gnu dot org
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
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).