From 7cc05eb4300d3d9c60161898cd9bb9078eacbed5 Mon Sep 17 00:00:00 2001
From: simonmar <unknown>
Date: Mon, 4 Sep 2000 14:10:38 +0000
Subject: [PATCH] [project @ 2000-09-04 14:10:38 by simonmar] Convert one of
the alternatives in an algebraic switch into the default, if we don't already
have a default. This generates better code in particular for inline
comparison primops.
Noticed by: Qrczak
---
ghc/compiler/absCSyn/AbsCUtils.lhs | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/ghc/compiler/absCSyn/AbsCUtils.lhs b/ghc/compiler/absCSyn/AbsCUtils.lhs
index 7c7151af68f2..f380da953497 100644
--- a/ghc/compiler/absCSyn/AbsCUtils.lhs
+++ b/ghc/compiler/absCSyn/AbsCUtils.lhs
@@ -28,10 +28,11 @@ import Unique ( Unique{-instance Eq-} )
import UniqSupply ( uniqFromSupply, uniqsFromSupply, splitUniqSupply,
UniqSupply )
import CmdLineOpts ( opt_OutputLanguage, opt_EmitCExternDecls )
-import Maybes ( maybeToBool )
import PrimOp ( PrimOp(..), CCall(..), isDynamicTarget )
import Panic ( panic )
+import Maybe ( isJust )
+
infixr 9 `thenFlt`
\end{code}
@@ -101,8 +102,16 @@ mkAbsCStmtList' other r = other : r
mkAlgAltsCSwitch :: CAddrMode -> [(ConTag, AbstractC)] -> AbstractC -> AbstractC
mkAlgAltsCSwitch scrutinee tagged_alts deflt_absc
- = CSwitch scrutinee (adjust tagged_alts) deflt_absc
+ | isJust (nonemptyAbsC deflt_absc)
+ = CSwitch scrutinee (adjust tagged_alts) deflt_absc
+ | otherwise
+ = CSwitch scrutinee (adjust rest) first_alt
where
+ -- it's ok to convert one of the alts into a default if we don't already have
+ -- one, because this is an algebraic case and we're guaranteed that the tag
+ -- will match one of the branches.
+ ((tag,first_alt):rest) = tagged_alts
+
-- Adjust the tags in the switch to start at zero.
-- This is the convention used by primitive ops which return algebraic
-- data types. Why? Because for two-constructor types, zero is faster
--
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