From 20b25bc688b7a6257cb466d9c70c214dafa369c6 Mon Sep 17 00:00:00 2001
From: Simon Peyton Jones <simonpj@microsoft.com>
Date: Thu, 23 Aug 2012 16:35:55 +0100
Subject: [PATCH] Don't specialise on implicit-parameter arguments in Specalise
This is a fix for Trac #7101
MERGED from commit 2f08f709cfdace23a4e32d80a57af349f7cc785a
---
compiler/specialise/Specialise.lhs | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/compiler/specialise/Specialise.lhs b/compiler/specialise/Specialise.lhs
index 6892c9c6ad69..4307ff75dfe3 100644
--- a/compiler/specialise/Specialise.lhs
+++ b/compiler/specialise/Specialise.lhs
@@ -1573,10 +1573,7 @@ mkCallUDs :: Id -> [CoreExpr] -> UsageDetails
mkCallUDs f args
| not (want_calls_for f) -- Imported from elsewhere
|| null theta -- Not overloaded
- || not (all isClassPred theta)
- -- Only specialise if all overloading is on class params.
- -- In ptic, with implicit params, the type args
- -- *don't* say what the value of the implicit param is!
+ || not (all type_determines_value theta)
|| not (spec_tys `lengthIs` n_tyvars)
|| not ( dicts `lengthIs` n_dicts)
|| not (any interestingDict dicts) -- Note [Interesting dictionary arguments]
@@ -1603,6 +1600,13 @@ mkCallUDs f args
| otherwise = Nothing
want_calls_for f = isLocalId f || isInlinablePragma (idInlinePragma f)
+
+ type_determines_value pred = isClassPred pred && not (isIPPred pred)
+ -- Only specialise if all overloading is on non-IP *class* params,
+ -- because these are the ones whose *type* determines their *value*.
+ -- In ptic, with implicit params, the type args
+ -- *don't* say what the value of the implicit param is!
+ -- See Trac #7101
\end{code}
Note [Interesting dictionary arguments]
--
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