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author | Eric Botcazou <ebotcazou@adacore.com> | 2023-10-16 21:16:38 +0200 |
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committer | Marc Poulhiès <poulhies@adacore.com> | 2023-11-07 10:15:04 +0100 |
commit | a2e4afc6f6bd0fd3c3894a2192fcc09e0b60f0be (patch) | |
tree | e392f4cfef910e72c0edcbbc6ff6734c4cd4edb5 | |
parent | de4f7051af5a00c3127cfd5c77f1a5b6d4000e42 (diff) | |
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ada: Elide temporary for aliased array with unconstrained nominal subtype
When the array is initialized with the result of a call to a function whose
result type is unconstrained, then the result is allocated with its bounds,
so the array can be rewritten as a renaming of the result in this case too.
gcc/ada/
* exp_ch3.adb (Expand_N_Object_Declaration): Fold initialization
expression of Nominal_Subtype_Is_Constrained_Array constant into
the computation of Rewrite_As_Renaming and remove the constant.
Set it to True for an aliased array with unconstrained nominal
subtype if the subtype of the expression is also unconstrained.
-rw-r--r-- | gcc/ada/exp_ch3.adb | 47 |
1 files changed, 24 insertions, 23 deletions
diff --git a/gcc/ada/exp_ch3.adb b/gcc/ada/exp_ch3.adb index 511d4c0..f88ac7e 100644 --- a/gcc/ada/exp_ch3.adb +++ b/gcc/ada/exp_ch3.adb @@ -7348,13 +7348,6 @@ package body Exp_Ch3 is Rewrite_As_Renaming : Boolean := False; -- Whether to turn the declaration into a renaming at the end - Nominal_Subtype_Is_Constrained_Array : constant Boolean := - Comes_From_Source (Obj_Def) - and then Is_Array_Type (Typ) and then Is_Constrained (Typ); - -- Used to avoid rewriting as a renaming for constrained arrays, - -- which is only a problem for source arrays; others have the - -- correct bounds (see below). - -- Start of processing for Expand_N_Object_Declaration begin @@ -8098,10 +8091,25 @@ package body Exp_Ch3 is Is_Entity_Name (Original_Node (Obj_Def)) - -- Nor if it is effectively an unconstrained declaration + -- If we have "X : S := ...;", and S is a constrained array + -- subtype, then we cannot rename, because renamings ignore + -- the constraints of S, so that would change the semantics + -- (sliding would not occur on the initial value). This is + -- only a problem for source objects though, the others have + -- the correct bounds. + + and then not (Comes_From_Source (Obj_Def) + and then Is_Array_Type (Typ) + and then Is_Constrained (Typ)) + + -- Moreover, if we have "X : aliased S := "...;" and S is an + -- unconstrained array type, then we can rename only if the + -- initialization expression has an unconstrained subtype too, + -- because the bounds must be present within X. and then not (Is_Array_Type (Typ) - and then Is_Constr_Subt_For_UN_Aliased (Typ)) + and then Is_Constr_Subt_For_UN_Aliased (Typ) + and then Is_Constrained (Etype (Expr_Q))) -- We may use a renaming if the initialization expression is a -- captured function call that meets a few conditions. @@ -8109,23 +8117,16 @@ package body Exp_Ch3 is and then (Is_Renamable_Function_Call (Expr_Q) - -- Or else if it is a variable with OK_To_Rename set + -- Or else if it is a variable with OK_To_Rename set - or else (OK_To_Rename_Ref (Expr_Q) - and then not Special_Ret_Obj) + or else (OK_To_Rename_Ref (Expr_Q) + and then not Special_Ret_Obj) - -- Or else if it is a slice of such a variable - - or else (Nkind (Expr_Q) = N_Slice - and then OK_To_Rename_Ref (Prefix (Expr_Q)) - and then not Special_Ret_Obj)) - - -- If we have "X : S := ...;", and S is a constrained array - -- subtype, then we cannot rename, because renamings ignore - -- the constraints of S, so that would change the semantics - -- (sliding would not occur on the initial value). + -- Or else if it is a slice of such a variable - and then not Nominal_Subtype_Is_Constrained_Array; + or else (Nkind (Expr_Q) = N_Slice + and then OK_To_Rename_Ref (Prefix (Expr_Q)) + and then not Special_Ret_Obj)); -- If the type needs finalization and is not inherently limited, -- then the target is adjusted after the copy and attached to the |