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, 8 insertions, 0 deletions

diff --git a/test/func-vla.c b/test/func-vla.c
new file mode 100644
index 0000000..6718c05
--- /dev/null
+++ b/test/func-vla.c
@@ -0,0 +1,8 @@
+int f(int n, long long (*a)[n]) {
+	return sizeof *a;
+}
+
+int main(void) {
+	long long a[5];
+	return f(5, &a) != sizeof a;
+}