Precompute static closures for DataCons with zero-width argswip/romes/isNullaryRepDataCon

Relax the predicate over nullary datacons that determines whether we can
return a precomputed static closure for them, such that we give
precomputed static closures to both datacon workers and wrappers as long
as they only take zero-width arguments (and hence their closure is
comprised of just the constructor info).

Previously, we would only allow datacons that were nullary with regard
to their Core representation, which prevented datacons workers with only
zero-width arguments and wrappers with none from using a precomputed
static closure.

See Note [Precomputed static closures of nullary constructors]

Closes #23158

1 files changed, 7 insertions, 1 deletions

diff --git a/compiler/GHC/StgToCmm/Closure.hs b/compiler/GHC/StgToCmm/Closure.hs
index fc76664d94..56cd91596e 100644
--- a/compiler/GHC/StgToCmm/Closure.hs
+++ b/compiler/GHC/StgToCmm/Closure.hs
@@ -22,7 +22,7 @@ module GHC.StgToCmm.Closure (
         argPrimRep,
 
         NonVoid(..), fromNonVoid, nonVoidIds, nonVoidStgArgs,
-        assertNonVoidIds, assertNonVoidStgArgs,
+        assertNonVoidIds, assertNonVoidStgArgs, hasNoNonZeroWidthArgs,
 
         -- * LambdaFormInfo
         LambdaFormInfo,         -- Abstract
@@ -170,6 +170,12 @@ assertNonVoidStgArgs :: [StgArg] -> [NonVoid StgArg]
 assertNonVoidStgArgs args = assert (not (any (isZeroBitTy . stgArgType) args)) $
                             coerce args
 
+-- | Returns whether there are any arguments with a non-zero-width runtime
+-- representation.
+--
+-- Returns True if the datacon has no or /just/ zero-width arguments.
+hasNoNonZeroWidthArgs :: DataCon -> Bool
+hasNoNonZeroWidthArgs = all (isZeroBitTy . scaledThing) . dataConRepArgTys
 
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 --                Representations