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Re: Minimize downward code motion during reassociation
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Easwaran Raman <eraman at google dot com>
- Cc: gcc-patches at gcc dot gnu dot org, aoliva at gcc dot gnu dot org
- Date: Thu, 6 Dec 2012 10:10:19 +0100
- Subject: Re: Minimize downward code motion during reassociation
- References: <CAPK5YPYUsvoskSJTfqYn+FPyTY0qQqzSJQ05B4dAzt0oefn-Ug@mail.gmail.com> <CAFiYyc3OpkXDo_WbMAsAoYgwfL4q7fxVF4rmAiDOT=omA9k=GA@mail.gmail.com> <CAPK5YPb0f0BJ3Z_MTSuJ0_Gw6bsRETbM0yNs_W6VC8sB58Edig@mail.gmail.com> <CAFiYyc3KEsyNeLK25F+k72LiD+mE=WW1SDxD4msX38OoSf_sMA@mail.gmail.com> <CAPK5YPYPYoDK2f-LcRvmt+JrCEiuM-yAQrv=ecYGcCAGv0VS6w@mail.gmail.com> <CAFiYyc0-JKh07Dn37WO7z3coz1-fHDU17+cDqV=kWCQi7v3uFQ@mail.gmail.com> <CAPK5YPbabJ+2ZgjK3O2nqFdXkUBnD-1n5DaEJU8T7+=oiayn=g@mail.gmail.com> <CAFiYyc2OvKGkPH5xcsQv14ECww6nm8gOe9V=+XAFTD=FBkSZ5A@mail.gmail.com> <CAPK5YPZb5Wb2D0AW-VuT_A4hQoUTwm7kk1nVoYpTftE1JVOLJg@mail.gmail.com>
On Tue, Nov 6, 2012 at 1:54 AM, Easwaran Raman <eraman@google.com> wrote:
> I am unable to figure out the right way to handle the debug
> statements. What I tried was to find debug statements that use the SSA
> name defined by the statement I moved (using SSA_NAME_IMM_USE_NODE)
> and then moved them as well at the right place. Thus, if I have to
> move t1 = a + b down (after the definition of 'd'), I also moved all
> debug statements that use t1 after the new position of t1. That still
> caused use-before-def problems in ssa_verify. I noticed that the debug
> statements got modified behind the scenes causing these issues. Any
> hints on what is the right way to handle the debug statements would be
> very helpful.
I think you cannot (and should not) move debug statements. Instead you
have to invalidate them. Otherwise you'll introduce confusion as debug
info cannot handle overlapping live ranges.
But maybe Alex can clarify.
Richard.