A OP_PHISOURCE which is the only user of its operand
can be trivially eliminated. For example, in:
add %r6, ...
...
phisrc %rt, %r6
the phisrc can safely be eliminated if no other instruction use %r6.
With this patch it's rewritten as:
add %rt, ...
...
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
unssa.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/unssa.c b/unssa.c
index 397130e3..f0a1392f 100644
--- a/unssa.c
+++ b/unssa.c
@@ -30,6 +30,11 @@
#include <assert.h>
+static inline int nbr_pseudo_users(pseudo_t p)
+{
+ return ptr_list_size((struct ptr_list *)p->users);
+}
+
static int simplify_phi_node(struct instruction *phi, pseudo_t tmp)
{
pseudo_t target = phi->target;
@@ -72,6 +77,7 @@ static void replace_phi_node(struct instruction *phi)
// rewrite all it's phi_src to copy to a new tmp
FOR_EACH_PTR(phi->phi_list, p) {
struct instruction *def = p->def;
+ pseudo_t src;
if (p == VOID)
continue;
@@ -80,6 +86,21 @@ static void replace_phi_node(struct instruction *phi)
def->opcode = OP_COPY;
def->target = tmp;
+
+ // can we eliminate the copy?
+ src = def->phi_src;
+ if (src->type != PSEUDO_REG)
+ continue;
+ switch (nbr_pseudo_users(src)) {
+ struct instruction *insn;
+ case 1:
+ insn = src->def;
+ insn->target = tmp;
+ tmp->def = insn;
+ case 0:
+ kill_instruction(def);
+ def->bb = NULL;
+ }
} END_FOR_EACH_PTR(p);
if (!phi->bb)
--
2.10.2
--
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