From 2fd94d55731146d3c1ce4097a664df2f16fe410e Mon Sep 17 00:00:00 2001
From: Matthew Flatt <mflatt@racket-lang.org>
Date: Tue, 8 Jan 2019 18:07:31 -0700
Subject: [PATCH] repair to cp0 changes for single-value checking

original commit: 1d0d02a1fd01629a2b72b82e95b60084f5bff4fb
---
 mats/cp0.ms | 5 ++++-
 s/cp0.ss    | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/mats/cp0.ms b/mats/cp0.ms
index 255911553f..be4a8f0d46 100644
--- a/mats/cp0.ms
+++ b/mats/cp0.ms
@@ -2815,5 +2815,8 @@
                                            (fields x y))
                                          (if (make-posn 0 ,e) ,v 'other)))
                         posn-decl-expanded)
-   
+   (parameterize ([enable-cp0 #t] [#%$suppress-primitive-inlining #f])
+     (equivalent-expansion?
+      (expand/optimize '(let ([g1 (begin (unknown) (void))]) 10))
+      '(begin (unknown) 10)))
 )
diff --git a/s/cp0.ss b/s/cp0.ss
index 0de44ec923..68dc4e99d4 100644
--- a/s/cp0.ss
+++ b/s/cp0.ss
@@ -737,7 +737,10 @@
             (cond
              [(and (eq? ctxt 'effect) (simple? e2))
               e1]
-             [(and (eq? ctxt 'ignored) (simple1? e2))
+             [(and (eq? ctxt 'ignored) (simple1? e2)
+                   ;; don't move e1 into a single-value
+                   ;; position unless that's ok
+                   (single-valued? e1))
               e1]
              [else
               (let ([e1 (nanopass-case (Lsrc Expr) e1