Rubbish literals for all representations (#18983)

This patch cleans up the complexity around WW's `mk_absent_let` by
broadening the scope of `LitRubbish`. Rubbish literals now store the
`PrimRep` they represent and are ultimately lowered in Cmm.
This in turn allows absent literals of `VecRep` or `VoidRep`. The latter
allows absent literals for unlifted coercions, as requested in #18983.

I took the liberty to rewrite and clean up `Note [Absent fillers]` and
`Note [Rubbish values]` to account for the new implementation and to
make them more orthogonal in their description.

I didn't add a new regression test, as `T18982` already contains the
test in the ticket and its test output changes as expected.

Fixes #18983.

1 files changed, 0 insertions, 20 deletions

diff --git a/compiler/GHC/StgToCmm/Env.hs b/compiler/GHC/StgToCmm/Env.hs
index ebfff0185f..5f4ef641c4 100644
--- a/compiler/GHC/StgToCmm/Env.hs
+++ b/compiler/GHC/StgToCmm/Env.hs
@@ -17,7 +17,6 @@ module GHC.StgToCmm.Env (
 
         bindArgsToRegs, bindToReg, rebindToReg,
         bindArgToReg, idToReg,
-        getArgAmode, getNonVoidArgAmodes,
         getCgIdInfo,
         maybeLetNoEscape,
     ) where
@@ -26,10 +25,8 @@ module GHC.StgToCmm.Env (
 
 import GHC.Prelude
 
-import GHC.Core.TyCon
 import GHC.Platform
 import GHC.StgToCmm.Monad
-import GHC.StgToCmm.Utils
 import GHC.StgToCmm.Closure
 
 import GHC.Cmm.CLabel
@@ -40,7 +37,6 @@ import GHC.Cmm.Utils
 import GHC.Types.Id
 import GHC.Cmm.Graph
 import GHC.Types.Name
-import GHC.Stg.Syntax
 import GHC.Core.Type
 import GHC.Builtin.Types.Prim
 import GHC.Types.Unique.FM
@@ -162,22 +158,6 @@ cgLookupPanic id
               ])
 
 
---------------------
-getArgAmode :: NonVoid StgArg -> FCode CmmExpr
-getArgAmode (NonVoid (StgVarArg var)) = idInfoToAmode <$> getCgIdInfo var
-getArgAmode (NonVoid (StgLitArg lit)) = CmmLit <$> cgLit lit
-
-getNonVoidArgAmodes :: [StgArg] -> FCode [CmmExpr]
--- NB: Filters out void args,
---     so the result list may be shorter than the argument list
-getNonVoidArgAmodes [] = return []
-getNonVoidArgAmodes (arg:args)
-  | isVoidRep (argPrimRep arg) = getNonVoidArgAmodes args
-  | otherwise = do { amode  <- getArgAmode (NonVoid arg)
-                   ; amodes <- getNonVoidArgAmodes args
-                   ; return ( amode : amodes ) }
-
-
 ------------------------------------------------------------------------
 --        Interface functions for binding and re-binding names
 ------------------------------------------------------------------------