reuse previous address constants in fold()

parseref() has code to reuse address constants, but this is not
done in other passes such as fold or isel. Introduce a new function
newcon() which takes a Con and returns a Ref for that constant, and
use this whenever creating address constants.

This is necessary to fix folding of address constants when one
operand is already folded. For example, in

	%a =l add $x, 1
	%b =l add %a, 2
	%c =w loadw %b

%a and %b were folded to $x+1 and $x+3 respectively, but then the
second add is visited again since it uses %a. This gets folded to
$x+3 as well, but as a new distinct constant. This results in %b
getting labeled as bottom instead of either constant, disabling the
replacement of %b by a constant in subsequent instructions (such
as the loadw).

1 files changed, 19 insertions, 0 deletions

diff --git a/util.c b/util.c
index 9a3576a..c8b0b9c 100644
--- a/util.c
+++ b/util.c
@@ -350,6 +350,25 @@ chuse(Ref r, int du, Fn *fn)
 }
 
 Ref
+newcon(Con *c0, Fn *fn)
+{
+	Con *c1;
+	int i;
+
+	for (i=0; i<fn->ncon; i++) {
+		c1 = &fn->con[i];
+		if (c0->type == c1->type
+		&& c0->bits.i == c1->bits.i
+		&& c0->label == c1->label
+		&& c0->local == c1->local)
+			return CON(i);
+	}
+	vgrow(&fn->con, ++fn->ncon);
+	fn->con[i] = *c0;
+	return CON(i);
+}
+
+Ref
 getcon(int64_t val, Fn *fn)
 {
 	int c;