[Bug tree-optimization/87126] [9 Regression] ICE on valid code at -Os and above on x86_64-linux-gnu: in vn_reference_insert, at tree-ssa-sccvn.c:2698

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87126

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
So when we disentangle the irreducible region we expose a disconnect between
the current execution flow and the RPO iteration.  This means we insert the
load d.2_4 = d; with the VDEF of the later processed store d = e_10; which
then triggers the assert.  We do run into the DEF in vn_reference_lookup_3
but that doesn't handle this simple case given we expect it to be handled
by visiting the def before the use ...

This shows the assert triggers on missed optimizations which means we
can as well remove it.

Better strategies for irreducible regions would include re-computing
RPO order on-the fly when necessary.