Module header tidyup #2

[ghc-hetmet.git] / compiler / simplCore / Simplify.lhs

diff --git a/compiler/simplCore/Simplify.lhs b/compiler/simplCore/Simplify.lhs
index 404a77f..bec02e6 100644 (file)
--- a/compiler/simplCore/Simplify.lhs
+++ b/compiler/simplCore/Simplify.lhs
@@ -1195,10 +1195,12 @@ mkAtomicArgsE :: SimplEnv
              -> SimplM FloatsWithExpr
 
 mkAtomicArgsE env is_strict (Cast rhs co) thing_inside
+  | not (exprIsTrivial rhs)
        -- Note [Float coersions]
+       -- See also Note [Take care] below
   = do { id <- newId FSLIT("a") (exprType rhs)
        ; completeNonRecX env False id id rhs $ \ env ->
-         thing_inside env (Cast (Var id) co) }
+         thing_inside env (Cast (substExpr env (Var id)) co) }
 
 mkAtomicArgsE env is_strict rhs thing_inside
   | (Var fun, args) <- collectArgs rhs,                                -- It's an application
@@ -1218,7 +1220,18 @@ mkAtomicArgsE env is_strict rhs thing_inside
        | otherwise
        = do { arg_id <- newId FSLIT("a") arg_ty
             ; completeNonRecX env False {- pessimistic -} arg_id arg_id arg $ \env ->
-              go env (App fun (Var arg_id)) args }
+              go env (App fun (substExpr env (Var arg_id))) args }
+               -- Note [Take care]:
+               -- If completeNonRecX was to do a postInlineUnconditionally
+               -- (undoing the effect of introducing the let-binding), we'd find arg_id had
+               -- no binding; hence the substExpr.  This happens if we see
+               --      C (D x `cast` g)
+               -- Then we start by making a variable a1, thus
+               --      let a1 = D x `cast` g in C a1
+               -- But then we deal with the rhs of a1, getting
+               --      let a2 = D x, a1 = a1 `cast` g in C a1
+               -- And now the preInlineUnconditionally kicks in, and we substitute for a1
+       
        where
          arg_ty = exprType arg
          no_float_arg = not is_strict && (isUnLiftedType arg_ty) && not (exprOkForSpeculation arg)
@@ -1233,6 +1246,7 @@ mkAtomicArgs :: Bool      -- OK to float unlifted args
                                                  -- if the strict-binding flag is on
 
 mkAtomicArgs ok_float_unlifted (Cast rhs co)
+  | not (exprIsTrivial rhs)
        -- Note [Float coersions]
   = do { id <- newId FSLIT("a") (exprType rhs)
        ; (binds, rhs') <- mkAtomicArgs ok_float_unlifted rhs