boot2

commit edbea61f7462e1584d862564470647372b578594
parent f725b1162f0038013abb884ca73dd3b10a7ddb89
Author: Ryan Sepassi <rsepassi@gmail.com>
Date:   Sun, 26 Apr 2026 21:52:48 -0700

cc tests: lock in unsigned narrowing zero-extends (§A.5)

Pre-existing mask-on-unsigned-narrow path is already correct;
cc-cg/19-zext-narrow + cc-parse/19-zext-narrow are regression guards
that pin the contrast with §A.4: same -3 source, same cast chain
shape, divergent result via target signedness (i32 → -3, u32 → 253).

Diffstat:
M
docs/CC-PUNCHLIST.md
 | 
10
++++++----
A
tests/cc-cg/19-zext-narrow.expected-exit
 | 
1
+
A
tests/cc-cg/19-zext-narrow.scm
 | 
20
++++++++++++++++++++
A
tests/cc-parse/19-zext-narrow.c
 | 
6
++++++
A
tests/cc-parse/19-zext-narrow.expected-exit
 | 
1
+

5 files changed, 34 insertions(+), 4 deletions(-)
diff --git a/docs/CC-PUNCHLIST.md b/docs/CC-PUNCHLIST.md
@@ -74,10 +74,12 @@ upstream of nearly everything else. Land this first.
     the canonical sign-extended 64-bit form. The widening cast back
     (relabel-only) preserves it.
 
-- [ ] **Unsigned narrowing zero-extends**
-  - cg: `cc-cg/NN-zext-narrow.scm` — `(unsigned)(unsigned char)-3` → 253.
-  - parse: `cc-parse/NN-zext-narrow.c`
-  - Needs: `cg-cast` zero-fill on unsigned target.
+- [x] **Unsigned narrowing zero-extends**
+  - cg: `cc-cg/19-zext-narrow.scm` — `(unsigned)(unsigned char)-3 == 253`.
+  - parse: `cc-parse/19-zext-narrow.c`
+  - Done: pre-existing mask-on-unsigned-narrow path was already
+    correct; fixture locks the contrast with §A.4 in (same source,
+    same chain shape, divergent result via target signedness).
 
 - [ ] **Integer promotion preserves sign across operations**
   - cg: `cc-cg/NN-promote-sign.scm` — operate on a `signed char` slot
diff --git a/tests/cc-cg/19-zext-narrow.expected-exit b/tests/cc-cg/19-zext-narrow.expected-exit
@@ -0,0 +1 @@
+1
diff --git a/tests/cc-cg/19-zext-narrow.scm b/tests/cc-cg/19-zext-narrow.scm
@@ -0,0 +1,20 @@
+;; tests/cc-cg/19-zext-narrow.scm — unsigned narrowing zero-extends
+;; (§A.5 of docs/CC-PUNCHLIST.md).
+;;
+;; Models: ((unsigned)(unsigned char)-3) == 253.
+;; The narrowing cast to u8 must mask off the high bits (not sign-
+;; extend), so the value 0xFFFFFFFD becomes 0xFD = 253. The
+;; widening cast back to u32 is relabel-only and preserves it.
+;; Locks in the contrast with §A.4: same source value, but the
+;; unsigned target arrives at 253 not -3.
+
+(let ((cg (cg-init)))
+  (cg-fn-begin cg "main" '() %t-i32)
+  (cg-push-imm cg %t-i32 -3)
+  (cg-cast cg %t-u8)
+  (cg-cast cg %t-u32)
+  (cg-push-imm cg %t-u32 253)
+  (cg-binop cg 'eq)
+  (cg-return cg)
+  (cg-fn-end cg)
+  (write-bv-fd 1 (cg-finish cg)))
diff --git a/tests/cc-parse/19-zext-narrow.c b/tests/cc-parse/19-zext-narrow.c
@@ -0,0 +1,6 @@
+// tests/cc-parse/19-zext-narrow.c — unsigned narrowing zero-extends.
+// §A.5 of docs/CC-PUNCHLIST.md.
+
+int main() {
+    return ((unsigned)(unsigned char)-3) == 253;
+}
diff --git a/tests/cc-parse/19-zext-narrow.expected-exit b/tests/cc-parse/19-zext-narrow.expected-exit
@@ -0,0 +1 @@
+1