Commit 526cbc7a authored by Jan Stolarek's avatar Jan Stolarek

Document deprecations in Hoopl

parent 5f64b2c6
-- Todo: remove -fno-warn-warnings-deprecations
-- See Note [Deprecations in Hoopl] in Hoopl module
{-# OPTIONS_GHC -fno-warn-warnings-deprecations #-}
module CmmBuildInfoTables
( CAFSet, CAFEnv, cafAnal
......@@ -2,6 +2,7 @@
{-# LANGUAGE ScopedTypeVariables #-}
-- See Note [Deprecations in Hoopl] in Hoopl module
{-# OPTIONS_GHC -fno-warn-warnings-deprecations #-}
module CmmLive
......@@ -124,3 +124,30 @@ badd_rw :: BwdRewrite UniqSM n f
-> (Graph n e x, BwdRewrite UniqSM n f)
-> (Graph n e x, BwdRewrite UniqSM n f)
badd_rw rw2 (g, rw1) = (g, rw1 `thenBwdRw` rw2)
-- Note [Deprecations in Hoopl]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- CmmLive and CmmBuildInfoTables modules enable -fno-warn-warnings-deprecations
-- flag because they import deprecated functions from Hoopl. I spent some time
-- trying to figure out what is going on, so here's a brief explanation. The
-- culprit is the joinOutFacts function, which should be replaced with
-- joinFacts. The difference between them is that the latter one needs extra
-- Label parameter. Labels identify blocks and are used in the fact base to
-- assign facts to a block (in case you're wondering, Label is an Int wrapped in
-- a newtype). Lattice join function is also required to accept a Label but the
-- only reason why it is so are the debugging purposes: see joinInFacts function
-- which is a no-op and is run only because join function might produce
-- debugging output. Now, going back to the Cmm modules. The "problem" with the
-- deprecated joinOutFacts function is that it passes wrong label when calling
-- lattice join function: instead of label of a block for which we are joining
-- facts it uses labels of successors of that block. So the joinFacts function
-- expects to be given a label of a block for which we are joining facts. I
-- don't see an obvious way of recovering that Label at the call sites of
-- joinOutFacts (if that was easily done then joinFacts function could do it
-- internally without requiring label as a parameter). A cheap way of
-- eliminating these warnings would be to create a bogus Label, since none of
-- our join functions is actually using the Label parameter. But that doesn't
-- feel right. I think the real solution here is to fix Hoopl API, which is
-- already broken in several ways. See Hoopl/Cleanup page on the wiki for more
-- notes on improving Hoopl.
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