diff options
| -rw-r--r-- | compiler/GHC/Core.hs | 2 | ||||
| -rw-r--r-- | compiler/GHC/Types/Var/Env.hs | 24 |
2 files changed, 24 insertions, 2 deletions
diff --git a/compiler/GHC/Core.hs b/compiler/GHC/Core.hs index 9a52e96eae..2e41f9932b 100644 --- a/compiler/GHC/Core.hs +++ b/compiler/GHC/Core.hs @@ -1131,6 +1131,8 @@ data RuleOpts = RuleOpts , roBignumRules :: !Bool -- ^ Enable rules for bignums } +-- | The 'InScopeSet' in the 'InScopeEnv' is a /superset/ of variables that are +-- currently in scope. See Note [The InScopeSet invariant]. type RuleFun = RuleOpts -> InScopeEnv -> Id -> [CoreExpr] -> Maybe CoreExpr type InScopeEnv = (InScopeSet, IdUnfoldingFun) diff --git a/compiler/GHC/Types/Var/Env.hs b/compiler/GHC/Types/Var/Env.hs index ee9e2d399b..683face5c9 100644 --- a/compiler/GHC/Types/Var/Env.hs +++ b/compiler/GHC/Types/Var/Env.hs @@ -98,7 +98,11 @@ import GHC.Utils.Outputable ************************************************************************ -} --- | A set of variables that are in scope at some point +-- | A set of variables that are in scope at some point. +-- +-- Note that this is a /superset/ of the variables that are currently in scope. +-- See Note [The InScopeSet invariant]. +-- -- "Secrets of the Glasgow Haskell Compiler inliner" Section 3.2 provides -- the motivation for this abstraction. newtype InScopeSet = InScope VarSet @@ -110,6 +114,21 @@ newtype InScopeSet = InScope VarSet -- lookup is useful (see, for instance, Note [In-scope set as a -- substitution]). + -- Note [The InScopeSet invariant] + -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + -- The InScopeSet must include every in-scope variable, but it may also + -- include other variables. + + -- Its principal purpose is to provide a set of variables to be avoided + -- when creating a fresh identifier (fresh in the sense that it does not + -- "shadow" any in-scope binding). To do this we simply have to find one that + -- does not appear in the InScopeSet. This is done by the key function + -- GHC.Types.Var.Env.uniqAway. + + -- See "Secrets of the Glasgow Haskell Compiler inliner" Section 3.2 + -- for more detailed motivation. #20419 has further discussion. + + instance Outputable InScopeSet where ppr (InScope s) = text "InScope" <+> @@ -182,7 +201,8 @@ since they are only locally unique. In particular, two successive calls to -} -- | @uniqAway in_scope v@ finds a unique that is not used in the --- in-scope set, and gives that to v. See Note [Local uniques]. +-- in-scope set, and gives that to v. See Note [Local uniques] and +-- Note [The InScopeSet invariant]. uniqAway :: InScopeSet -> Var -> Var -- It starts with v's current unique, of course, in the hope that it won't -- have to change, and thereafter uses the successor to the last derived unique |