From: Simon Peyton Jones <simonpj@microsoft.com>
Date: Sat, 11 Jun 2011 13:21:39 +0000 (+0100)
Subject: Comments only
X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=commitdiff_plain;h=769f5c90a96742beec5e1870e68b3c7f21d9e573

Comments only
---

diff --git a/compiler/coreSyn/CoreUtils.lhs b/compiler/coreSyn/CoreUtils.lhs
index 4146b62..19ac62f 100644
--- a/compiler/coreSyn/CoreUtils.lhs
+++ b/compiler/coreSyn/CoreUtils.lhs
@@ -592,6 +592,12 @@ exprIsCheap' good_app other_expr 	-- Applications and variables
     go_pap args = all (exprIsCheap' good_app) args
         -- Used to be "all exprIsTrivial args" due to concerns about
         -- duplicating nested constructor applications, but see #4978.
+	-- The principle here is that 
+	--    let x = a +# b in c *# x
+        -- should behave equivalently to
+        --    c *# (a +# b)
+        -- Since lets with cheap RHSs are accepted, 
+        -- so should paps with cheap arguments
 
     --------------
     go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args