From 8d4ea7263f4f5c0ad2ba06749a04198c84e58689 Mon Sep 17 00:00:00 2001
From: Troels Henriksen <athas@sigkill.dk>
Date: Thu, 2 Feb 2023 12:17:21 +0100
Subject: [PATCH] Catch this error.

---
 src/Futhark/Pass/Flatten.hs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/Futhark/Pass/Flatten.hs b/src/Futhark/Pass/Flatten.hs
index 31658db74a..24e487d1d2 100644
--- a/src/Futhark/Pass/Flatten.hs
+++ b/src/Futhark/Pass/Flatten.hs
@@ -359,6 +359,8 @@ transformDistBasicOp segments env (inps, res, pe, aux, e) =
             i <- letExp "i" =<< toExp (pe64 o' + flat_i)
             pure (i, v')
           pure $ insertIrregular shape flags offsets (distResTag res) elems' env
+      | otherwise ->
+          error "Flattening update: destination is not input."
     _ -> error $ "Unhandled BasicOp:\n" ++ prettyString e
   where
     scalarCase =