From 9a4af2c451baa685492ed576447c3ce2e335427d Mon Sep 17 00:00:00 2001
From: Simon Peyton Jones <simonpj@microsoft.com>
Date: Fri, 23 Dec 2016 10:04:23 +0000
Subject: Comments only

---
 compiler/simplCore/SimplCore.hs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/compiler/simplCore/SimplCore.hs b/compiler/simplCore/SimplCore.hs
index ca869dc8dd..8e9a9c68bb 100644
--- a/compiler/simplCore/SimplCore.hs
+++ b/compiler/simplCore/SimplCore.hs
@@ -344,6 +344,8 @@ getCoreToDo dflags
         -- Final run of the demand_analyser, ensures that one-shot thunks are
         -- really really one-shot thunks. Only needed if the demand analyser
         -- has run at all. See Note [Final Demand Analyser run] in DmdAnal
+        -- It is EXTREMELY IMPORTANT to run this pass, otherwise execution
+        -- can become /exponentially/ more expensive. See Trac #11731, #12996.
         runWhen (strictness || late_dmd_anal) CoreDoStrictness,
 
         maybe_rule_check (Phase 0)
-- 
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