From c8e47177fccb1af0c0f082a2836f53c86d3a652d Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Wed, 2 Jan 2019 12:05:32 -0800
Subject: [PATCH] Add an assert to `append_ebb_params_for_function_params`.

---
 lib/frontend/src/frontend.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/frontend/src/frontend.rs b/lib/frontend/src/frontend.rs
index 2ed09fbd01..d769b678f8 100644
--- a/lib/frontend/src/frontend.rs
+++ b/lib/frontend/src/frontend.rs
@@ -405,6 +405,11 @@ impl<'a> FunctionBuilder<'a> {
     /// parameters. This can be used to set up the ebb parameters for the
     /// entry block.
     pub fn append_ebb_params_for_function_params(&mut self, ebb: Ebb) {
+        debug_assert!(
+            !self.func_ctx.ssa.has_any_predecessors(ebb),
+            "ebb parameters for function parameters should only be added to the entry block"
+        );
+
         // These parameters count as "user" parameters here because they aren't
         // inserted by the SSABuilder.
         let user_param_count = &mut self.func_ctx.ebbs[ebb].user_param_count;