From 699e26e0fc295341f7618adb2441eaba5f5c8677 Mon Sep 17 00:00:00 2001
From: Denys Zadorozhnyi <denys@zadorozhnyi.com>
Date: Thu, 19 Oct 2023 12:53:52 +0300
Subject: [PATCH] chore: add a debug assert to not allow declaring a block
 predecessor twice

---
 frontend-wasm/src/ssa.rs | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/frontend-wasm/src/ssa.rs b/frontend-wasm/src/ssa.rs
index c83dc5c3..ee769f28 100644
--- a/frontend-wasm/src/ssa.rs
+++ b/frontend-wasm/src/ssa.rs
@@ -324,7 +324,18 @@ impl SSABuilder {
     /// Callers are expected to avoid adding the same predecessor more than once in the case
     /// of a jump table.
     pub fn declare_block_predecessor(&mut self, block: Block, inst: Inst) {
-        debug_assert!(!self.is_sealed(block));
+        debug_assert!(
+            !self.is_sealed(block),
+            "you cannot add a predecessor to a sealed block"
+        );
+        debug_assert!(
+            self.ssa_blocks[block]
+                .predecessors
+                .as_slice(&self.inst_pool)
+                .iter()
+                .all(|&branch| branch != inst),
+            "you have declared the same predecessor twice!"
+        );
         self.ssa_blocks[block]
             .predecessors
             .push(inst, &mut self.inst_pool);