When PRE discovers a full redundancy during insertion it cannot unite
the two value sets. Instead it inserts a copy old-val = new-val where
new-val can also be a constant. The following looks through such
copies during elimination, providing one extra level of constant and
copy propagation. For the PR this helps avoiding a bogus diagnostic
that's emitted on unreachable code during loop optimization.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
Richard.
PR tree-optimization/110204
* tree-ssa-sccvn.cc (eliminate_dom_walker::eliminate_avail):
Look through copies generated by PRE.
---
gcc/tree-ssa-sccvn.cc | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index 11061a374a2..a0b98c18ac8 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -6594,7 +6594,22 @@ eliminate_dom_walker::eliminate_avail (basic_block, tree
op)
if (SSA_NAME_IS_DEFAULT_DEF (valnum))
return valnum;
if (avail.length () > SSA_NAME_VERSION (valnum))
- return avail[SSA_NAME_VERSION (valnum)];
+ {
+ tree av = avail[SSA_NAME_VERSION (valnum)];
+ /* When PRE discovers a new redundancy there's no way to unite
+ the value classes so it instead inserts a copy old-val = new-val.
+ Look through such copies here, providing one more level of
+ simplification at elimination time. */
+ gassign *ass;
+ if (av && (ass = dyn_cast <gassign *> (SSA_NAME_DEF_STMT (av))))
+ if (gimple_assign_rhs_class (ass) == GIMPLE_SINGLE_RHS)
+ {
+ tree rhs1 = gimple_assign_rhs1 (ass);
+ if (CONSTANT_CLASS_P (rhs1) || TREE_CODE (rhs1) == SSA_NAME)
+ av = rhs1;
+ }
+ return av;
+ }
}
else if (is_gimple_min_invariant (valnum))
return valnum;
--
2.35.3
