------- Comment #29 from matz at gcc dot gnu dot org 2010-07-07 12:10 ------- [just for completeness to not lose the thought:] Thinking about this some more (triggered by the problem of not having nice back edges in irreducible loops), it's not really the back edges that are interesting but the underlying property of SSA, namely the correspondence between static single assignments and dynamic single assignments: The alias oracle will give correct answers only for memory references when it can infer runtime equality of values from syntactic equality, which it can for a correct SSA program.
So, if M1 and M2 (two memrefs) contain mentions of syntactically the same values, then A1/A2 (two accesses to M1/M2) have to be dominated by the dynamically same definitions of those values. For SSA form that's trivially true, for RTL of course it isn't. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44838
