These trivial phi-nodes have all their sources but one
which are defined by the phi-node itself . This typically
arise if a var is presetn in a loop and only set in the
loop header.
In this case, the only possible value for the phi-node and
these sources is the value of the other unique source.
These phi-nodes can this easily be replaced by this value
avoiding firther unwanted processing.
This patch remove these trivial phi-nodes in most, simple
cases.
More complex cases need more complex method to get rid of them.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
ssa.c | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 87 insertions(+)
diff --git a/ssa.c b/ssa.c
index 9d532dbf6..1b7f7cda3 100644
--- a/ssa.c
+++ b/ssa.c
@@ -16,6 +16,92 @@
static pseudo_t load_var_(struct basic_block*, struct symbol*, unsigned long);
+static inline void concat_user_list(struct pseudo_user_list *src, struct pseudo_user_list **dst)
+{
+ concat_ptr_list((struct ptr_list *)src, (struct ptr_list **)dst);
+}
+
+/*
+ * Go through the "insn->users" list and replace them all..
+ */
+static void convert_phi(struct instruction *insn, pseudo_t src)
+{
+ pseudo_t phi = insn->target;
+ struct pseudo_user *pu;
+
+ assert(phi != src);
+ if (phi == src)
+ return;
+ FOR_EACH_PTR(phi->users, pu) {
+ pseudo_t *pp = pu->userp;
+ pseudo_t p = *pp;
+
+ if (p == VOID)
+ continue;
+ assert(p == phi);
+ if (p->def->src == phi)
+ continue;
+ *pu->userp = src;
+ } END_FOR_EACH_PTR(pu);
+ if (has_use_list(src))
+ concat_user_list(phi->users, &src->users);
+ phi->users = NULL;
+}
+
+static void kill_phi_node(struct instruction *node)
+{
+ struct pseudo_list *phi_list = node->phi_list;
+ pseudo_t phi;
+
+ node->phi_list = NULL;
+ node->bb = NULL;
+ FOR_EACH_PTR(phi_list, phi) {
+ struct instruction *phisrc;
+ if (phi == VOID)
+ continue;
+ phisrc = phi->def;
+ remove_use(&phisrc->src);
+ phisrc->bb = NULL;
+ } END_FOR_EACH_PTR(phi);
+ free_ptr_list(&node->phi_list);
+}
+
+static pseudo_t try_remove_trivial_phi(pseudo_t phi)
+{
+ struct instruction *node = phi->def;
+ pseudo_t same = NULL;
+ pseudo_t p;
+
+ if (phi == VOID)
+ return phi;
+ if (phi->type != PSEUDO_REG)
+ return phi;
+ if (node->opcode != OP_PHI)
+ return phi;
+ FOR_EACH_PTR(node->phi_list, p) {
+ pseudo_t src;
+
+ if (p == VOID)
+ continue;
+ src = p->def->src;
+ if (src == same || src == phi)
+ continue;
+ if (same)
+ return phi;
+ same = src;
+ } END_FOR_EACH_PTR(p);
+
+ if (same == NULL)
+ same = undef_pseudo();
+
+ convert_phi(node, same);
+ phi->target = same;
+ phi->type = PSEUDO_INDIR;
+ kill_phi_node(node);
+
+ return same;
+}
+
// FIXME: -> common file
static void append_instruction(struct basic_block *bb, struct instruction *insn)
{
@@ -38,6 +124,7 @@ static pseudo_t add_phi_operand(struct symbol *var, pseudo_t phi, unsigned long
use_pseudo(node, src, add_pseudo(&node->phi_list, src));
src->ident = var->ident;
} END_FOR_EACH_PTR(parent);
+ phi = try_remove_trivial_phi(phi);
return phi;
}
--
2.14.0
--
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