https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85757
Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |kugan at gcc dot gnu.org, | |rguenth at gcc dot gnu.org --- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> --- This is the failure to handle non-aliasing stores. We get it recorded here: /* If this is a store, remember it or bail out if we have multiple ones (the will be in different CFG parts then). */ else if (gimple_vdef (use_stmt)) { if (temp) { fail = true; BREAK_FROM_IMM_USE_STMT (ui); } temp = use_stmt; } but that's necessary for the walking algorithm. Basically PHI handling was added for a few ad-hoc cases. diff --git a/gcc/tree-ssa-dse.c b/gcc/tree-ssa-dse.c index 9220fea7f2e..ab5aa5bb314 100644 --- a/gcc/tree-ssa-dse.c +++ b/gcc/tree-ssa-dse.c @@ -569,7 +569,8 @@ dse_classify_store (ao_ref *ref, gimple *stmt, gimple **use_stmt, See gcc.c-torture/execute/20051110-*.c. */ else if (gimple_code (use_stmt) == GIMPLE_PHI) { - if (temp + if ((temp + && stmt_may_clobber_ref_p_1 (temp, ref)) /* Make sure we are not in a loop latch block. */ || gimple_bb (stmt) == gimple_bb (use_stmt) || dominated_by_p (CDI_DOMINATORS, "solves" half of it. But the above snipped needs similar treatment for the case of temp being the PHI. Basically a more programatical approach of walking the individual paths into the PHI node is required which, for clarity, should require refactoring of the walk. walk_nonaliased_vuses and friends may or may not be a good copying source.