From e82b1eed9f9d749afb1e47f0bc8f35e806fda9f6 Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom@tomsmeding.com>
Date: Wed, 5 Nov 2025 22:29:41 +0100
Subject: Some extra Map optimisations

---
 src/Simplify.hs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

(limited to 'src/Simplify.hs')

diff --git a/src/Simplify.hs b/src/Simplify.hs
index 1889adc..19d0c17 100644
--- a/src/Simplify.hs
+++ b/src/Simplify.hs
@@ -185,6 +185,21 @@ simplify'Rec = \case
   ELet _ e1 (ENil _) | STNil <- typeOf e1 ->
     acted $ simplify' e1
 
+  -- map (\_ -> x) e  ~>  build (shape e) (\_ -> x)
+  EMap _ e1 e2
+    | Occ Zero Zero <- occCount IZ e1
+    , STArr n _ <- typeOf e2 ->
+    acted $ simplify' $
+      EBuild ext n (EShape ext e2) $
+        subst (\_ t' -> \case IZ -> error "Unused variable was used"
+                              IS i -> EVar ext t' (IS i))
+              e1
+
+  -- vertical fusion
+  EMap _ e1 (EMap _ e2 e3) ->
+    acted $ simplify' $
+      EMap ext (ELet ext e2 (weakenExpr (WCopy WSink) e1)) e3
+
   -- projection down-commuting
   EFst _ (ECase _ e1 e2 e3) ->
     acted $ simplify' $
-- 
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