Implement variable length arrays

Variably modified types are required for C23.

Since QBE doesn't currently support saving and restoring the stack
pointer, a current limitation is that we can't reclaim stack space
from VLAs that go out of scope. This is potentially problematic for
VLAs appearing in a loop, but this case is uncommon enough that it
is silently ignored for now.

Implements: https://todo.sr.ht/~mcf/cproc/1
References: https://todo.sr.ht/~mcf/cproc/88
Co-authored-by: Michael Forney <mforney@mforney.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/test/vla-nested.c b/test/vla-nested.c
new file mode 100644
index 0000000..176392e
--- /dev/null
+++ b/test/vla-nested.c
@@ -0,0 +1,13 @@
+int l;
+int f(int x) {
+	l += x;
+	return x;
+}
+int main(void) {
+	int r = 0;
+	int (*p[f(2)])[f(3)];
+	r += l != 5;
+	r += sizeof p != sizeof(int (*[2])[3]);
+	r += sizeof **p != sizeof(int[3]);
+	return r;
+}