GenStgAlt 3-tuple synonym --> Record type

This commit alters GenStgAlt from a type synonym to a Record with field
accessors. In pursuit of #21078, this is not a required change but cleans
up several areas for nicer code in the upcoming js-backend, and in GHC
itself.

GenStgAlt: 3-tuple -> record

Stg.Utils: GenStgAlt 3-tuple -> record

Stg.Stats: StgAlt 3-tuple --> record

Stg.InferTags.Rewrite: StgAlt 3-tuple -> record

Stg.FVs: GenStgAlt 3-tuple -> record

Stg.CSE: GenStgAlt 3-tuple -> record

Stg.InferTags: GenStgAlt 3-tuple --> record

Stg.Debug: GenStgAlt 3-tuple --> record

Stg.Lift.Analysis: GenStgAlt 3-tuple --> record

Stg.Lift: GenStgAlt 3-tuple --> record

ByteCode.Instr: GenStgAlt 3-tuple --> record

Stg.Syntax: add GenStgAlt helper functions

Stg.Unarise: GenStgAlt 3-tuple --> record

Stg.BcPrep: GenStgAlt 3-tuple --> record

CoreToStg: GenStgAlt 3-tuple --> record

StgToCmm.Expr: GenStgAlt 3-tuple --> record

StgToCmm.Bind: GenStgAlt 3-tuple --> record

StgToByteCode: GenStgAlt 3-tuple --> record

Stg.Lint: GenStgAlt 3-tuple --> record

Stg.Syntax: strictify GenStgAlt

GenStgAlt: add haddock, some cleanup

fixup: remove calls to pure, single ViewPattern

StgToByteCode: use case over viewpatterns

2 files changed, 11 insertions, 8 deletions

diff --git a/compiler/GHC/StgToCmm/Bind.hs b/compiler/GHC/StgToCmm/Bind.hs
index 5507173dc7..e8539d80f5 100644
--- a/compiler/GHC/StgToCmm/Bind.hs
+++ b/compiler/GHC/StgToCmm/Bind.hs
@@ -285,7 +285,9 @@ mkRhsClosure    profile _ _check_tags bndr _cc
   , StgCase (StgApp scrutinee [{-no args-}])
          _   -- ignore bndr
          (AlgAlt _)
-         [(DataAlt _, params, sel_expr)] <- strip expr
+         [GenStgAlt{ alt_con   = DataAlt _
+                   , alt_bndrs = params
+                   , alt_rhs   = sel_expr}] <- strip expr
   , StgApp selectee [{-no args-}] <- strip sel_expr
   , the_fv == scrutinee                -- Scrutinee is the only free variable
 
diff --git a/compiler/GHC/StgToCmm/Expr.hs b/compiler/GHC/StgToCmm/Expr.hs
index 55892b8789..7992e34417 100644
--- a/compiler/GHC/StgToCmm/Expr.hs
+++ b/compiler/GHC/StgToCmm/Expr.hs
@@ -459,7 +459,7 @@ job we deleted the hacks.
 
 cgCase (StgApp v []) _ (PrimAlt _) alts
   | isVoidRep (idPrimRep v)  -- See Note [Scrutinising VoidRep]
-  , [(DEFAULT, _, rhs)] <- alts
+  , [GenStgAlt{alt_con=DEFAULT, alt_bndrs=_, alt_rhs=rhs}] <- alts
   = cgExpr rhs
 
 {- Note [Dodgy unsafeCoerce 1]
@@ -652,9 +652,10 @@ chooseReturnBndrs :: Id -> AltType -> [CgStgAlt] -> [NonVoid Id]
 chooseReturnBndrs bndr (PrimAlt _) _alts
   = assertNonVoidIds [bndr]
 
-chooseReturnBndrs _bndr (MultiValAlt n) [(_, ids, _)]
+chooseReturnBndrs _bndr (MultiValAlt n) [alt]
   = assertPpr (ids `lengthIs` n) (ppr n $$ ppr ids $$ ppr _bndr) $
     assertNonVoidIds ids     -- 'bndr' is not assigned!
+    where ids = alt_bndrs alt
 
 chooseReturnBndrs bndr (AlgAlt _) _alts
   = assertNonVoidIds [bndr]  -- Only 'bndr' is assigned
@@ -669,11 +670,11 @@ chooseReturnBndrs _ _ _ = panic "chooseReturnBndrs"
 cgAlts :: (GcPlan,ReturnKind) -> NonVoid Id -> AltType -> [CgStgAlt]
        -> FCode ReturnKind
 -- At this point the result of the case are in the binders
-cgAlts gc_plan _bndr PolyAlt [(_, _, rhs)]
-  = maybeAltHeapCheck gc_plan (cgExpr rhs)
+cgAlts gc_plan _bndr PolyAlt [alt]
+  = maybeAltHeapCheck gc_plan (cgExpr $ alt_rhs alt)
 
-cgAlts gc_plan _bndr (MultiValAlt _) [(_, _, rhs)]
-  = maybeAltHeapCheck gc_plan (cgExpr rhs)
+cgAlts gc_plan _bndr (MultiValAlt _) [alt]
+  = maybeAltHeapCheck gc_plan (cgExpr $ alt_rhs alt)
         -- Here bndrs are *already* in scope, so don't rebind them
 
 cgAlts gc_plan bndr (PrimAlt _) alts
@@ -942,7 +943,7 @@ cgAltRhss gc_plan bndr alts = do
   let
     base_reg = idToReg platform bndr
     cg_alt :: CgStgAlt -> FCode (AltCon, CmmAGraphScoped)
-    cg_alt (con, bndrs, rhs)
+    cg_alt GenStgAlt{alt_con=con, alt_bndrs=bndrs, alt_rhs=rhs}
       = getCodeScoped             $
         maybeAltHeapCheck gc_plan $
         do { _ <- bindConArgs con base_reg (assertNonVoidIds bndrs)