fix bug in alias analysis

The handling of phi was incorrect
and we would sometimes miss escapes.
We now handle phis at the very end
of the pass to make sure the defs
for their arguments have all been
processed.

2 files changed, 26 insertions, 3 deletions

diff --git a/alias.c b/alias.c
index 3885115..9b41084 100644
--- a/alias.c
+++ b/alias.c
@@ -132,7 +132,7 @@ store(Ref r, int sz, Fn *fn)
 void
 fillalias(Fn *fn)
 {
-	uint n, m;
+	uint n;
 	int t, sz;
 	int64_t x;
 	Blk *b;
@@ -146,8 +146,6 @@ fillalias(Fn *fn)
 	for (n=0; n<fn->nblk; ++n) {
 		b = fn->rpo[n];
 		for (p=b->phi; p; p=p->link) {
-			for (m=0; m<p->narg; m++)
-				esc(p->arg[m], fn);
 			assert(rtype(p->to) == RTmp);
 			a = &fn->tmp[p->to.val].alias;
 			assert(a->type == ABot);
@@ -217,4 +215,8 @@ fillalias(Fn *fn)
 		if (b->jmp.type != Jretc)
 			esc(b->jmp.arg, fn);
 	}
+	for (b=fn->start; b; b=b->link)
+		for (p=b->phi; p; p=p->link)
+			for (n=0; n<p->narg; n++)
+				esc(p->arg[n], fn);
 }
diff --git a/test/alias1.ssa b/test/alias1.ssa
new file mode 100644
index 0000000..a064fac
--- /dev/null
+++ b/test/alias1.ssa
@@ -0,0 +1,21 @@
+export function w $main() {
+@start
+	%a =l alloc4 4
+	%b =l alloc4 4
+	storew 4, %a
+	storew 5, %b
+
+@loop
+	# %mem will be %a and %b successively,
+	# but we do not know it when processing
+	# the phi because %b goes through a cpy
+	%mem =l phi @start %a, @loop %bcpy
+
+	%w =w load %mem
+	%eq5 =w ceqw %w, 5
+	%bcpy =l copy %b
+	jnz %eq5, @exit, @loop
+
+@exit
+	ret 0
+}