https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109002
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- When doing partial PRE we somehow lose the effect of g = 1; we also generate weird PHIs: <bb 2> pretmp_20 = h; pretmp_22 = g; <bb 3> # prephitmp_21 = PHI <pretmp_20(2), prephitmp_25(10)> # prephitmp_23 = PHI <pretmp_22(2), prephitmp_24(10)> # prephitmp_24 = PHI <pretmp_22(2), prephitmp_24(10)> # prephitmp_25 = PHI <pretmp_20(2), prephitmp_25(10)> those are all unnecessary ... There's one old detail I never understood in partial ANTIC compute and that gets us weird expressions in here, which is that we do not PHI translate ANTIC_IN when computing PA_OUT. Fixing that fixes this bug. I have no idea how to create a testcase for the testsuite though besides verifying we're not inserting any PHI - but we also fail to partial-PRE the load of h here, likely because of the iteration order imposed by the infinite loop which is probably also key to the miscompilation. Anyway, I have a fix, but I'm not 100% sure it fixes the actual cause.
