Inline implication constraints

[ghc-hetmet.git] / compiler / typecheck / TcSimplify.lhs

diff --git a/compiler/typecheck/TcSimplify.lhs b/compiler/typecheck/TcSimplify.lhs
index 5b654fc..769068b 100644 (file)
--- a/compiler/typecheck/TcSimplify.lhs
+++ b/compiler/typecheck/TcSimplify.lhs
@@ -1014,7 +1014,9 @@ makeImplicationBind loc all_tvs reft
              tup_ty = mkTupleTy Boxed n_dict_irreds (map idType dict_irred_ids)
              pat = TuplePat (map nlVarPat dict_irred_ids) Boxed tup_ty
              rhs = L span (mkHsWrap co (HsVar (instToId implic_inst)))
-             co  = mkWpApps (map instToId dict_givens) <.> mkWpTyApps eq_tyvar_cos <.> mkWpTyApps (mkTyVarTys all_tvs)
+             co  = mkWpApps (map instToId dict_givens)
+                   <.> mkWpTyApps eq_tyvar_cos
+                   <.> mkWpTyApps (mkTyVarTys all_tvs)
              bind | [dict_irred_id] <- dict_irred_ids  = VarBind dict_irred_id rhs
                   | otherwise        = PatBind { pat_lhs = L span pat, 
                                                  pat_rhs = unguardedGRHSs rhs, 
@@ -2216,8 +2218,13 @@ reduceImplication env orig_avails name reft tvs extra_givens wanteds inst_loc
                        -- SLPJ Sept07: this looks Utterly Wrong to me, but I think
                        --              that current extra_givens has no EqInsts, so
                        --              it makes no difference
-               -- dict_ids = map instToId extra_givens
-               co  = mkWpTyLams tvs <.> mkWpTyLams eq_tyvars <.> mkWpLams dict_ids <.> WpLet (binds `unionBags` bind)
+               co  = wrap_inline       -- Note [Always inline implication constraints]
+                     <.> mkWpTyLams tvs
+                     <.> mkWpTyLams eq_tyvars
+                     <.> mkWpLams dict_ids
+                     <.> WpLet (binds `unionBags` bind)
+               wrap_inline | null dict_ids = idHsWrapper
+                           | otherwise     = WpInline
                rhs = mkHsWrap co payload
                loc = instLocSpan inst_loc
                payload | [dict_wanted] <- dict_wanteds = HsVar (instToId dict_wanted)
@@ -2232,6 +2239,16 @@ reduceImplication env orig_avails name reft tvs extra_givens wanteds inst_loc
     }
 \end{code}
 
+Note [Always inline implication constraints]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Suppose an implication constraint floats out of an INLINE function.
+Then although the implication has a single call site, it won't be 
+inlined.  And that is bad because it means that even if there is really
+*no* overloading (type signatures specify the exact types) there will
+still be dictionary passing in the resulting code.  To avert this,
+we mark the implication constraints themselves as INLINE, at least when
+there is no loss of sharing as a result.
+
 Note [Reducing implication constraints]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Suppose we are trying to simplify