* [Ada] Potentially unevaluated nested expressions
@ 2020-07-10 9:44 Pierre-Marie de Rodat
0 siblings, 0 replies; only message in thread
From: Pierre-Marie de Rodat @ 2020-07-10 9:44 UTC (permalink / raw)
To: gcc-patches; +Cc: Javier Miranda
[-- Attachment #1: Type: text/plain, Size: 392 bytes --]
This patch fixes the general problem in the detection of potentially
unevaluated nested expressions.
Tested on x86_64-pc-linux-gnu, committed on trunk
gcc/ada/
* sem_util.adb
(Immediate_Context_Implies_Is_Potentially_Unevaluated): New
subprogram.
(Is_Potentially_Unevaluated): Do not stop climbing the tree on
the first candidate subexpression; required to handle nested
expressions.
[-- Attachment #2: patch.diff --]
[-- Type: text/x-diff, Size: 8892 bytes --]
diff --git a/gcc/ada/sem_util.adb b/gcc/ada/sem_util.adb
--- a/gcc/ada/sem_util.adb
+++ b/gcc/ada/sem_util.adb
@@ -17752,6 +17752,13 @@ package body Sem_Util is
-- return True if the others choice of the given array aggregate does
-- not cover any component (i.e. is null).
+ function Immediate_Context_Implies_Is_Potentially_Unevaluated
+ (Expr : Node_Id) return Boolean;
+ -- Return True if the *immediate* context of this expression tells us
+ -- that it is potentially unevaluated; return False if the *immediate*
+ -- context doesn't provide an answer to this question and we need to
+ -- keep looking.
+
function Non_Static_Or_Null_Range (N : Node_Id) return Boolean;
-- Return True if the given range is nonstatic or null
@@ -17789,6 +17796,99 @@ package body Sem_Util is
return False;
end Has_Null_Others_Choice;
+ ----------------------------------------------------------
+ -- Immediate_Context_Implies_Is_Potentially_Unevaluated --
+ ----------------------------------------------------------
+
+ function Immediate_Context_Implies_Is_Potentially_Unevaluated
+ (Expr : Node_Id) return Boolean
+ is
+ Par : constant Node_Id := Parent (Expr);
+
+ begin
+ if Nkind (Par) = N_If_Expression then
+ return Is_Elsif (Par) or else Expr /= First (Expressions (Par));
+
+ elsif Nkind (Par) = N_Case_Expression then
+ return Expr /= Expression (Par);
+
+ elsif Nkind_In (Par, N_And_Then, N_Or_Else) then
+ return Expr = Right_Opnd (Par);
+
+ elsif Nkind_In (Par, N_In, N_Not_In) then
+
+ -- If the membership includes several alternatives, only the first
+ -- is definitely evaluated.
+
+ if Present (Alternatives (Par)) then
+ return Expr /= First (Alternatives (Par));
+
+ -- If this is a range membership both bounds are evaluated
+
+ else
+ return False;
+ end if;
+
+ elsif Nkind (Par) = N_Quantified_Expression then
+ return Expr = Condition (Par);
+
+ elsif Nkind (Par) = N_Aggregate
+ and then Present (Etype (Par))
+ and then Etype (Par) /= Any_Composite
+ and then Is_Array_Type (Etype (Par))
+ and then Nkind (Expr) = N_Component_Association
+ then
+ declare
+ Choice : Node_Id;
+ In_Others_Choice : Boolean := False;
+
+ begin
+ -- The expression of an array_component_association is
+ -- potentially unevaluated if the associated choice is a
+ -- subtype_indication or range that defines a nonstatic or
+ -- null range.
+
+ Choice := First (Choices (Expr));
+ while Present (Choice) loop
+ if Nkind (Choice) = N_Range
+ and then Non_Static_Or_Null_Range (Choice)
+ then
+ return True;
+
+ elsif Nkind (Choice) = N_Identifier
+ and then Present (Scalar_Range (Etype (Choice)))
+ and then
+ Non_Static_Or_Null_Range (Scalar_Range (Etype (Choice)))
+ then
+ return True;
+
+ elsif Nkind (Choice) = N_Others_Choice then
+ In_Others_Choice := True;
+ end if;
+
+ Next (Choice);
+ end loop;
+
+ -- It is also potentially unevaluated if the associated choice
+ -- is an others choice and the applicable index constraint is
+ -- nonstatic or null.
+
+ if In_Others_Choice then
+ if not Compile_Time_Known_Bounds (Etype (Par)) then
+ return True;
+ else
+ return Has_Null_Others_Choice (Par);
+ end if;
+ end if;
+ end;
+
+ return False;
+
+ else
+ return False;
+ end if;
+ end Immediate_Context_Implies_Is_Potentially_Unevaluated;
+
------------------------------
-- Non_Static_Or_Null_Range --
------------------------------
@@ -17850,25 +17950,27 @@ package body Sem_Util is
-- conjunct in a postcondition) with a potentially unevaluated operand.
Par := Parent (Expr);
- while not Nkind_In (Par, N_And_Then,
- N_Case_Expression,
- N_If_Expression,
- N_In,
- N_Not_In,
- N_Or_Else,
- N_Quantified_Expression)
- and then not (Nkind (Par) = N_Aggregate
- and then Etype (Par) /= Any_Composite
- and then Is_Array_Type (Etype (Par)))
+
+ while Present (Par)
+ and then Nkind (Par) /= N_Pragma_Argument_Association
loop
- Expr := Par;
- Par := Parent (Par);
+ if Comes_From_Source (Par)
+ and then
+ Immediate_Context_Implies_Is_Potentially_Unevaluated (Expr)
+ then
+ return True;
+
+ -- For component associations continue climbing; it may be part of
+ -- an array aggregate.
+
+ elsif Nkind (Par) = N_Component_Association then
+ null;
-- If the context is not an expression, or if is the result of
-- expansion of an enclosing construct (such as another attribute)
-- the predicate does not apply.
- if Nkind (Par) = N_Case_Expression_Alternative then
+ elsif Nkind (Par) = N_Case_Expression_Alternative then
null;
elsif Nkind (Par) not in N_Subexpr
@@ -17876,87 +17978,12 @@ package body Sem_Util is
then
return False;
end if;
- end loop;
-
- if Nkind (Par) = N_If_Expression then
- return Is_Elsif (Par) or else Expr /= First (Expressions (Par));
-
- elsif Nkind (Par) = N_Case_Expression then
- return Expr /= Expression (Par);
-
- elsif Nkind_In (Par, N_And_Then, N_Or_Else) then
- return Expr = Right_Opnd (Par);
-
- elsif Nkind_In (Par, N_In, N_Not_In) then
-
- -- If the membership includes several alternatives, only the first is
- -- definitely evaluated.
-
- if Present (Alternatives (Par)) then
- return Expr /= First (Alternatives (Par));
-
- -- If this is a range membership both bounds are evaluated
-
- else
- return False;
- end if;
-
- elsif Nkind (Par) = N_Quantified_Expression then
- return Expr = Condition (Par);
-
- elsif Nkind (Par) = N_Aggregate
- and then Etype (Par) /= Any_Composite
- and then Is_Array_Type (Etype (Par))
- and then Nkind (Expr) = N_Component_Association
- then
- declare
- Choice : Node_Id;
- In_Others_Choice : Boolean := False;
-
- begin
- -- The expression of an array_component_association is potentially
- -- unevaluated if the associated choice is a subtype_indication or
- -- range that defines a nonstatic or null range.
-
- Choice := First (Choices (Expr));
- while Present (Choice) loop
- if Nkind (Choice) = N_Range
- and then Non_Static_Or_Null_Range (Choice)
- then
- return True;
-
- elsif Nkind (Choice) = N_Identifier
- and then Present (Scalar_Range (Etype (Choice)))
- and then
- Non_Static_Or_Null_Range (Scalar_Range (Etype (Choice)))
- then
- return True;
-
- elsif Nkind (Choice) = N_Others_Choice then
- In_Others_Choice := True;
- end if;
-
- Next (Choice);
- end loop;
-
- -- It is also potentially unevaluated if the associated choice
- -- is an others choice and the applicable index constraint is
- -- nonstatic or null.
-
- if In_Others_Choice then
- if not Compile_Time_Known_Bounds (Etype (Par)) then
- return True;
- else
- return Has_Null_Others_Choice (Par);
- end if;
- end if;
- end;
- return False;
+ Expr := Par;
+ Par := Parent (Par);
+ end loop;
- else
- return False;
- end if;
+ return False;
end Is_Potentially_Unevaluated;
-----------------------------------------
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