diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/coreSyn/CoreUnfold.hs | 43 |
1 files changed, 38 insertions, 5 deletions
diff --git a/compiler/coreSyn/CoreUnfold.hs b/compiler/coreSyn/CoreUnfold.hs index 11c2a7533e..3ac35c9848 100644 --- a/compiler/coreSyn/CoreUnfold.hs +++ b/compiler/coreSyn/CoreUnfold.hs @@ -47,7 +47,7 @@ import GhcPrelude import DynFlags import CoreSyn import PprCore () -- Instances -import OccurAnal ( occurAnalyseExpr ) +import OccurAnal ( occurAnalyseExpr_NoBinderSwap ) import CoreOpt import CoreArity ( manifestArity ) import CoreUtils @@ -101,7 +101,7 @@ mkDFunUnfolding :: [Var] -> DataCon -> [CoreExpr] -> Unfolding mkDFunUnfolding bndrs con ops = DFunUnfolding { df_bndrs = bndrs , df_con = con - , df_args = map occurAnalyseExpr ops } + , df_args = map occurAnalyseExpr_NoBinderSwap ops } -- See Note [Occurrence analysis of unfoldings] mkWwInlineRule :: DynFlags -> CoreExpr -> Arity -> Unfolding @@ -311,7 +311,7 @@ mkCoreUnfolding :: UnfoldingSource -> Bool -> CoreExpr -> UnfoldingGuidance -> Unfolding -- Occurrence-analyses the expression before capturing it mkCoreUnfolding src top_lvl expr guidance - = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr, + = CoreUnfolding { uf_tmpl = occurAnalyseExpr_NoBinderSwap expr, -- See Note [Occurrence analysis of unfoldings] uf_src = src, uf_is_top = top_lvl, @@ -330,7 +330,7 @@ mkUnfolding :: DynFlags -> UnfoldingSource -- Calculates unfolding guidance -- Occurrence-analyses the expression before capturing it mkUnfolding dflags src is_top_lvl is_bottoming expr - = CoreUnfolding { uf_tmpl = occurAnalyseExpr expr, + = CoreUnfolding { uf_tmpl = occurAnalyseExpr_NoBinderSwap expr, -- See Note [Occurrence analysis of unfoldings] uf_src = src, uf_is_top = is_top_lvl, @@ -342,7 +342,7 @@ mkUnfolding dflags src is_top_lvl is_bottoming expr where is_top_bottoming = is_top_lvl && is_bottoming guidance = calcUnfoldingGuidance dflags is_top_bottoming expr - -- NB: *not* (calcUnfoldingGuidance (occurAnalyseExpr expr))! + -- NB: *not* (calcUnfoldingGuidance (occurAnalyseExpr_NoBinderSwap expr))! -- See Note [Calculate unfolding guidance on the non-occ-anal'd expression] {- @@ -364,6 +364,39 @@ But more generally, the simplifier is designed on the basis that it is looking at occurrence-analysed expressions, so better ensure that they acutally are. +We use occurAnalyseExpr_NoBinderSwap instead of occurAnalyseExpr; +see Note [No binder swap in unfoldings]. + +Note [No binder swap in unfoldings] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The binder swap can temporarily violate Core Lint, by assinging +a LocalId binding to a GlobalId. For example, if A.foo{r872} +is a GlobalId with unique r872, then + + case A.foo{r872} of bar { + K x -> ...(A.foo{r872})... + } + +gets transformed to + + case A.foo{r872} of bar { + K x -> let foo{r872} = bar + in ...(A.foo{r872})... + +This is usually not a problem, because the simplifier will transform +this to: + + case A.foo{r872} of bar { + K x -> ...(bar)... + +However, after occurrence analysis but before simplification, this extra 'let' +violates the Core Lint invariant that we do not have local 'let' bindings for +GlobalIds. That seems (just) tolerable for the occurrence analysis that happens +just before the Simplifier, but not for unfoldings, which are Linted +independently. +As a quick workaround, we disable binder swap in this module. +See Trac #16288 and #16296 for further plans. + Note [Calculate unfolding guidance on the non-occ-anal'd expression] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Notice that we give the non-occur-analysed expression to |