From f9e3a52eaa6ae91388aa247182da6df3cc8d5a05 Mon Sep 17 00:00:00 2001
From: lemon <lsof@mailbox.org>
Date: Sun, 22 Mar 2026 10:45:22 +0100
Subject: mem2reg: fix rare edge case with weird control flow

mem2reg was assuming alloca's appeared before all their uses. When this
didn't happen it broke the logic re. sealed blocks. Normally this
doesn't happen in most natural code. Even with gotos, RPO would assure
this in most cases, the exception I found is a goto that jumps into a
loop past a variable declaration that is earlier in the loop. Then even
RPO would keep the alloca itself past the first uses, breaking things.
---
 test/18-goto2.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 test/18-goto2.c

(limited to 'test')

diff --git a/test/18-goto2.c b/test/18-goto2.c
new file mode 100644
index 0000000..8742d35
--- /dev/null
+++ b/test/18-goto2.c
@@ -0,0 +1,24 @@
+/* EXPECT:
+ok
+*/
+
+void h(int x){}
+
+/* isolated mem2reg bug from something in regalloc: the goto into the loop past
+ * the `int nqueue` declaration caused a miscompilation */
+void test(void) {
+   int curi = 5;
+   goto start2;
+   for (curi; curi >= 0; curi--) {
+      int nqueue;
+   start2:
+      for (nqueue = 2; nqueue > 0; ) {
+         h(nqueue--);
+      }
+   }
+}
+int puts(const char *);
+int main(void) {
+   test();
+   puts("ok");
+}
-- 
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