select: simplify handling of constant cond or src1 == src2

If the operands of a select instruction are identical, then
this select can be replaced by its operand.
If the condition of a select is a constant, the this select
can be replaced by one of its condition, depending on the
truth value of the condition.

This simplification is already done but:
* when src1 == src2, the condition's value is tested although
  it may not be a constant. It's kinda OK because in all case
  one of the operand will be selected and both are identical
  but it's a bit weird and unclean.
* since the instruction will be replaced, the usage of its
  condition and operands must be removed. This is done here but
  the kill_instruction() inside replace_with_pseudo() take
  already care of this.

So, separate the two cases and simply use replace_with_pseudo()
for both without bothering killing the operands.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>

1 files changed, 6 insertions, 8 deletions

diff --git a/simplify.c b/simplify.c
index 20ea5f1b..20ab9b3b 100644
--- a/simplify.c
+++ b/simplify.c
@@ -1753,14 +1753,12 @@ static int simplify_select(struct instruction *insn)
 	cond = insn->src1;
 	src1 = insn->src2;
 	src2 = insn->src3;
-	if (constant(cond) || src1 == src2) {
-		pseudo_t *kill, take;
-		kill_use(&insn->src1);
-		take = cond->value ? src1 : src2;
-		kill = cond->value ? &insn->src3 : &insn->src2;
-		kill_use(kill);
-		return replace_with_pseudo(insn, take);
-	}
+
+	if (constant(cond))
+		return replace_with_pseudo(insn, cond->value ? src1 : src2);
+	if (src1 == src2)
+		return replace_with_pseudo(insn, src1);
+
 	if (constant(src1) && constant(src2)) {
 		long long val1 = src1->value;
 		long long val2 = src2->value;