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, 2 insertions, 5 deletions

diff --git a/amd64/isel.c b/amd64/isel.c
index 607c176..0f4c7a5 100644
--- a/amd64/isel.c
+++ b/amd64/isel.c
@@ -117,12 +117,9 @@ fixarg(Ref *r, int k, Ins *i, Fn *fn)
 		m = &fn->mem[r0.val];
 		if (req(m->base, R))
 		if (m->offset.type == CAddr) {
-			n = fn->ncon;
-			vgrow(&fn->con, ++fn->ncon);
-			fn->con[n] = m->offset;
-			m->offset.type = CUndef;
 			r0 = newtmp("isel", Kl, fn);
-			emit(Oaddr, Kl, r0, CON(n), R);
+			emit(Oaddr, Kl, r0, newcon(&m->offset, fn), R);
+			m->offset.type = CUndef;
 			m->base = r0;
 		}
 	}