We can handle _1 = PHI <_1, _2> as a copy.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
PR tree-optimization/84646
* tree-ssa-forwprop.cc (pass_forwprop::execute): Improve
copy propagation across PHIs.
---
gcc/tree-ssa-forwprop.cc | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
index 4b693ef095c..7c7942600ef 100644
--- a/gcc/tree-ssa-forwprop.cc
+++ b/gcc/tree-ssa-forwprop.cc
@@ -3384,7 +3384,12 @@ pass_forwprop::execute (function *fun)
FOR_EACH_PHI_ARG (use_p, phi, it, SSA_OP_USE)
{
tree use = USE_FROM_PTR (use_p);
- if (! first)
+ if (use == res)
+ /* The PHI result can also appear on a backedge, if so
+ we can ignore this case for the purpose of determining
+ the singular value. */
+ ;
+ else if (! first)
first = use;
else if (! operand_equal_p (first, use, 0))
{
--
2.35.3
