From 35587eba3feb609bc6de3a290e7e47641137f946 Mon Sep 17 00:00:00 2001
From: Simon Peyton Jones <simon.peytonjones@gmail.com>
Date: Thu, 26 Oct 2023 11:50:26 +0100
Subject: [PATCH] Fix a bug in tail calls with ticks
See #24078 for the diagnosis. The change affects only
the Tick case of occurrence analysis.
It's a bit hard to test, so no regression test (yet anyway).
---
compiler/GHC/Core/Opt/OccurAnal.hs | 46 ++++++++++++++++--------------
1 file changed, 24 insertions(+), 22 deletions(-)
diff --git a/compiler/GHC/Core/Opt/OccurAnal.hs b/compiler/GHC/Core/Opt/OccurAnal.hs
index a4af26f1496a..38dad20c0a63 100644
--- a/compiler/GHC/Core/Opt/OccurAnal.hs
+++ b/compiler/GHC/Core/Opt/OccurAnal.hs
@@ -2493,32 +2493,34 @@ But it is not necessary to gather CoVars from the types of other binders.
-}
occAnal env (Tick tickish body)
- | SourceNote{} <- tickish
- = WUD usage (Tick tickish body')
- -- SourceNotes are best-effort; so we just proceed as usual.
- -- If we drop a tick due to the issues described below it's
- -- not the end of the world.
+ = WUD usage' (Tick tickish body')
+ where
+ WUD usage body' = occAnal env body
- | tickish `tickishScopesLike` SoftScope
- = WUD (markAllNonTail usage) (Tick tickish body')
+ usage'
+ | tickish `tickishScopesLike` SoftScope
+ = usage -- For soft-scoped ticks (including SourceNotes) we don't want
+ -- to lose join-point-hood, so we don't mess with `usage` (#24078)
- | Breakpoint _ _ ids _ <- tickish
- = WUD (addManyOccs usage_lam (mkVarSet ids)) (Tick tickish body')
- -- never substitute for any of the Ids in a Breakpoint
+ -- For a non-soft tick scope, we can inline lambdas only, so we
+ -- abandon tail calls, and do markAllInsideLam too: usage_lam
+
+ | Breakpoint _ _ ids _ <- tickish
+ = -- Never substitute for any of the Ids in a Breakpoint
+ addManyOccs usage_lam (mkVarSet ids)
+
+ | otherwise
+ = usage_lam
- | otherwise
- = WUD usage_lam (Tick tickish body')
- where
- (WUD usage body') = occAnal env body
- -- for a non-soft tick scope, we can inline lambdas only
usage_lam = markAllNonTail (markAllInsideLam usage)
- -- TODO There may be ways to make ticks and join points play
- -- nicer together, but right now there are problems:
- -- let j x = ... in tick<t> (j 1)
- -- Making j a join point may cause the simplifier to drop t
- -- (if the tick is put into the continuation). So we don't
- -- count j 1 as a tail call.
- -- See #14242.
+
+ -- TODO There may be ways to make ticks and join points play
+ -- nicer together, but right now there are problems:
+ -- let j x = ... in tick<t> (j 1)
+ -- Making j a join point may cause the simplifier to drop t
+ -- (if the tick is put into the continuation). So we don't
+ -- count j 1 as a tail call.
+ -- See #14242.
occAnal env (Cast expr co)
= let (WUD usage expr') = occAnal env expr
--
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