+
+isTrueLHsExpr :: LHsExpr Id -> Maybe (CoreExpr -> DsM CoreExpr)
+
+-- Returns Just {..} if we're sure that the expression is True
+-- I.e. * 'True' datacon
+-- * 'otherwise' Id
+-- * Trivial wappings of these
+-- The arguments to Just are any HsTicks that we have found,
+-- because we still want to tick then, even it they are aways evaluted.
+isTrueLHsExpr (L _ (HsVar v)) | v `hasKey` otherwiseIdKey
+ || v `hasKey` getUnique trueDataConId
+ = Just return
+ -- trueDataConId doesn't have the same unique as trueDataCon
+isTrueLHsExpr (L loc (HsTick ix frees e))
+ | Just ticks <- isTrueLHsExpr e = Just (ticks >=> mkTickBox ix frees)
+ -- This encodes that the result is constant True for Hpc tick purposes;
+ -- which is specifically what isTrueLHsExpr is trying to find out.
+isTrueLHsExpr (L loc (HsBinTick ixT _ e))
+ | Just ticks <- isTrueLHsExpr e = Just (ticks >=> mkTickBox ixT [])
+isTrueLHsExpr (L _ (HsPar e)) = isTrueLHsExpr e
+isTrueLHsExpr other = Nothing