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Diffstat (limited to 'compiler/GHC/Stg/InferTags.hs')
| -rw-r--r-- | compiler/GHC/Stg/InferTags.hs | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/compiler/GHC/Stg/InferTags.hs b/compiler/GHC/Stg/InferTags.hs index 2a42b4c7de..79acaa14f5 100644 --- a/compiler/GHC/Stg/InferTags.hs +++ b/compiler/GHC/Stg/InferTags.hs @@ -82,6 +82,8 @@ and will be tagged with `001` or `010` respectively. It will never point to a thunk, nor will it be tagged `000` (meaning "might be a thunk"). NB: Note that the proper tag for some objects is indeed `000`. Currently this is the case for PAPs. +This works analogous to how `StrictWorkerId`s work. See also Note [Strict Worker Ids]. + Why do we care? Because if we have code like: case strictPair of @@ -119,6 +121,8 @@ evaluated will allocate the constructor. So we do our best to establish that `x` is already tagged (which it almost always is) to avoid this cost. In my benchmarks I haven't seen any cases where this causes regressions. +Note that there are similar constraints around Note [Strict Worker Ids]. + Note [How untagged pointers can end up in strict fields] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider |