Zdenek Dvorak <[EMAIL PROTECTED]> wrote on 30/06/2007 09:55:45: > Hello, > > > By "this change" I mean just commenting out the check in > > doloop_condition_get. After applying the patch that introduced DOLOOP > > patterns for SPU (http://gcc.gnu.org/ml/gcc-patches/2007-01/msg01470.html) > > we needed this hack in order to be able to use the doloop_condition_get to > > return the register decremented by the branch instruction for any unrolled > > loop (The unroller changed originally GE loops to EQ ). Where can this check > > be required? Note that we did not touched the similar check in > > doloop_modify. We tested this on our SPU branch and saw no regressions. > > hmmm.... I see now that modulo-sched.c:doloop_register_get uses > doloop_condition_get, which is why this may affect something. Anyway, > changing doloop_condition_get is wrong. Just teach modulo-sched to use > number of iterations analysis from loop-iv.c instead of the > doloop_register_get hack, >
Here's my understanding. When the doloop pass looks at a loop, it's doloop_condition_get makes sure that the closing branch is of a certain form that doloop_modify can handle (with GE or NE condition only). Changing doloop_condition_get without a similar change to doloop_modify is expected to trigger some assert in doloop_modify, or specifically gcc_unreachable in case it sees an EQ condition. (A few passes later,) When the sms pass looks at a loop, it apparently sees this loop closed by an EQ branch, (whose target leaves the loop, and falling-through to a goto to the beginning of the loop?). This reversal is presumably related to unrolled loops. Vladimir, it could help if you show what the EQ closing branch and its target/fallthrough blocks in question look like. It doesn't seem that the number of iterations analysis from loop-iv.c deals with EQ closing branches. One option is for sms to use doloop_condition_get/loop-iv analysis in their current form, and if failed check (on our own) for reversed doloop patterns. Another is to try and reverse the closing branch before calling doloop_condition_get/loop-iv analysis; any suitable branch reversal facility available? Ayal.
