Simplification of BBs (via try_to_siplify_bb() or
simplify_branch_branch()) can only be done under
some conditions:
- the removed/bypassed BB is free of side-effects
- the removed/bypassed BB doesn't define some pseudos
needed later.
This last check is efficiently done by bb_depends_on()
using liveness info. However, there is no liveness
done on OP_PHI thus the dependencies involving OP_PHI
are missing, resulting in illegal simplifications.
Fix this by explicitly adding the missing dependencies.
Supersedes: 852801f8b966407544326cd1c485f9bc7681a2e6
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
flow.c | 31 +++++++++++++++----------------
1 file changed, 15 insertions(+), 16 deletions(-)
diff --git a/flow.c b/flow.c
index 536bf257f..23fa7c21b 100644
--- a/flow.c
+++ b/flow.c
@@ -81,26 +81,23 @@ static int bb_depends_on(struct basic_block *target, struct basic_block *src)
}
/*
- * This is only to be used by try_to_simplify_bb().
- * It really should be handled by bb_depends_on(), only
- * that there is no liveness done on OP_PHI/OP_PHISRC.
- * So we consider for now that if there is an OP_PHI
- * then some block in fact depends on this one.
- * The OP_PHI controling the conditional branch of this bb
- * is excluded since the branch will be removed.
+ * This really should be handled by bb_depends_on()
+ * which efficiently check the dependence using the
+ * defines - needs liveness info. Problem is that
+ * there is no liveness done on OP_PHI & OP_PHISRC.
+ *
+ * This function add the missing dependency checks.
*/
-static int bb_defines_phi(struct basic_block *bb, struct instruction *def)
+static int bb_depends_on_phi(struct basic_block *target, struct basic_block *src)
{
struct instruction *insn;
- FOR_EACH_PTR(bb->insns, insn) {
- switch (insn->opcode) {
- case OP_PHI:
- if (def && insn != def)
- return 1;
+ FOR_EACH_PTR(src->insns, insn) {
+ if (!insn->bb)
continue;
- default:
+ if (insn->opcode != OP_PHI)
continue;
- }
+ if (pseudo_in_list(target->needs, insn->target))
+ return 1;
} END_FOR_EACH_PTR(insn);
return 0;
}
@@ -153,7 +150,7 @@ static int try_to_simplify_bb(struct basic_block *bb, struct instruction *first,
target = true ? second->bb_true : second->bb_false;
if (bb_depends_on(target, bb))
continue;
- if (bb_defines_phi(bb, first))
+ if (bb_depends_on_phi(target, bb))
continue;
changed |= rewrite_branch(source, &br->bb_true, bb, target);
changed |= rewrite_branch(source, &br->bb_false, bb, target);
@@ -224,6 +221,8 @@ static int simplify_branch_branch(struct basic_block *bb, struct instruction *br
goto try_to_rewrite_target;
if (bb_depends_on(final, target))
goto try_to_rewrite_target;
+ if (bb_depends_on_phi(final, target))
+ return 0;
return rewrite_branch(bb, target_p, target, final);
try_to_rewrite_target:
--
2.13.2
--
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