[Git][ghc/ghc][wip/cfuneqcan-refactor] Comment that intermediate cached values do not help

[Richard Eisenberg]

Richard Eisenberg pushed to branch wip/cfuneqcan-refactor at Glasgow Haskell Compiler / GHC


Commits:
2b7af3cd by Richard Eisenberg at 2020-11-24T22:50:54+00:00
Comment that intermediate cached values do not help

- - - - -


1 changed file:

- compiler/GHC/Tc/Solver/Rewrite.hs


Changes:

=====================================
compiler/GHC/Tc/Solver/Rewrite.hs
=====================================
@@ -832,6 +832,9 @@ rewrite_exact_fam_app tc tys
     do { result3 <- try_to_reduce tc xis
        ; case result3 of
            Just (co, xi) -> finish True (homogenise xi co)
+            -- We could add an item to the cache relating F xis to the final result,
+            -- where xis is the result of STEP 3. But testing showed that this
+            -- leads to 10-20% regressions in the T9872x tests, so we don't do it.
            Nothing       -> -- we have made no progress at all: STEP 7.
                             return (homogenise reduced (mkTcReflCo role reduced))
              where



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/2b7af3cd500bb587736ff455645fb4cd5ff986f3

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/2b7af3cd500bb587736ff455645fb4cd5ff986f3
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