https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78411
--- Comment #8 from Richard Biener <rguenth at gcc dot gnu.org> ---
diff --git a/gcc/tree-ssa-pre.c b/gcc/tree-ssa-pre.c
index 4f17200..c50c598 100644
--- a/gcc/tree-ssa-pre.c
+++ b/gcc/tree-ssa-pre.c
@@ -3017,6 +3017,7 @@ insert_into_preds_of_block (basic_block block, unsigned
int exprnum,
}
/* Make the necessary insertions. */
+ bool all_constant = true;
FOR_EACH_EDGE (pred, ei, block->preds)
{
gimple_seq stmts = NULL;
@@ -3041,8 +3042,15 @@ insert_into_preds_of_block (basic_block block, unsigned
int exprnum,
if (is_gimple_min_invariant (builtexpr))
avail[pred->dest_idx] = get_or_alloc_expr_for_constant (builtexpr);
else
- avail[pred->dest_idx] = get_or_alloc_expr_for_name (builtexpr);
+ {
+ avail[pred->dest_idx] = get_or_alloc_expr_for_name (builtexpr);
+ all_constant = false;
+ }
}
+ /* If we're about to insert a PHI with all arguments constant refuse
+ to do that. But return whether we inserted stuff. */
+ if (all_constant)
+ return insertions;
/* If we didn't want a phi node, and we made insertions, we still have
inserted new stuff, and thus return true. If we didn't want a phi node,
and didn't make insertions, we haven't added anything new, so return
but that still leaves us with
_25 = MEM[base: products_16(D), index: i_35, step: 8, offset: 0B];
if (_25 > 0)
goto <bb 7>;
else
goto <bb 6>;
<bb 6>:
_17 = -_25;
<bb 7>:
# iftmp.0_13 = PHI <1(5), -1(6)>
# prephitmp_10 = PHI <_25(5), _17(6)>
_9 = (long long unsigned int) prephitmp_10;
and thus phiopt not matching the ABS. For some reason split-paths split
the loop latch confusing RTL if-conversion even more (removing the
possibility to emit a conditional store).
I don't believe what tree-if-conv.c did was reasonable here (together with PRE)
but we do not generate optimal code from the code in the testcase.
Still if-conversion is generally a RTL opt task.
