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, 19 insertions, 0 deletions

diff --git a/test/sizeof-vla.c b/test/sizeof-vla.c
new file mode 100644
index 0000000..16d6fa1
--- /dev/null
+++ b/test/sizeof-vla.c
@@ -0,0 +1,19 @@
+int c = 0;
+int main(void) {
+	int r = 0;
+	int l = 2;
+	int (*p)[l] = 0;
+	r += sizeof(c++, p) != sizeof(int (*)[]);       /* VM, but not VLA */
+	r += c != 0;
+	r += sizeof(*(c++, p)) != 2 * sizeof(int);      /* VLA */
+	r += c != 1;
+	r += sizeof(c++, *p) != sizeof(int *);          /* VLA decayed to pointer */
+	r += c != 1;
+	r += sizeof(int[++l]) != 3 * sizeof(int);       /* VLA */
+	r += l != 3;
+	r += sizeof(int[++l][1]) != sizeof(int[4][1]);  /* VLA */
+	r += l != 4;
+	r += sizeof(int[(c++, 5)]) != 5 * sizeof(int);  /* VLA */
+	r += c != 2;
+	return r;
+}