From: Eric Botcazou <[email protected]>
The alignment check for address clauses had historically been performed
universally by GNAT, until a decade ago when it was disabled by default
on non-strict-alignment platforms.
This seems questionable when an alignment clause is also given for the
entity since the intent is clear, so the change restores it as well as
its associated warning.
Moreover, this alignment check had historically been subsumed into the
language-defined Range_Check, until two decades ago when it became the
implementation-defined Alignment_Check, while still being part of the
Range_Check to ease the transition. Now is probably a good time to cut
the apron strings and make Alignment_Check standalone.
gcc/ada/ChangeLog:
* doc/gnat_rm/representation_clauses_and_pragmas.rst (Address
Clauses): Adjust description of alignment checks.
* sem_ch13.adb (Address_Clause_Check_Record): Remove now unused
Alignment_Checks_Suppressed component.
(Alignment_Checks_Suppressed): Delete.
(Analyze_Attribute_Definition_Clause) <Attribute_Alignment>: Do not
consider the status of range checks to decide whether to generate an
alignment check. Always generate it if an alignment clause is also
given for the entity.
<Attribute_Alignment>: Generate an alignment check if an address
clause is also given for the entity.
(Register_Address_Clause_Check): Adjust for above removal.
(Validate_Address_Clauses): Test the Check_Address_Alignment flag
on the clause to decide whether to give the warning.
* gnat_rm.texi: Regenerate.
* gnat_ugn.texi: Regenerate.
Tested on x86_64-pc-linux-gnu, committed on master.
---
.../representation_clauses_and_pragmas.rst | 3 +-
gcc/ada/gnat_rm.texi | 5 +-
gcc/ada/gnat_ugn.texi | 4 +-
gcc/ada/sem_ch13.adb | 50 +++++++------------
4 files changed, 23 insertions(+), 39 deletions(-)
diff --git a/gcc/ada/doc/gnat_rm/representation_clauses_and_pragmas.rst
b/gcc/ada/doc/gnat_rm/representation_clauses_and_pragmas.rst
index 7250f6586ee..65bb1877f7c 100644
--- a/gcc/ada/doc/gnat_rm/representation_clauses_and_pragmas.rst
+++ b/gcc/ada/doc/gnat_rm/representation_clauses_and_pragmas.rst
@@ -1580,8 +1580,7 @@ machines with strict alignment requirements, GNAT
checks (at compile time if possible, generating a warning, or at execution
time with a run-time check) that the alignment is appropriate. If the
run-time check fails, then ``Program_Error`` is raised. This run-time
-check is suppressed if range checks are suppressed, or if the special GNAT
-check Alignment_Check is suppressed, or if
+check is suppressed if the GNAT check Alignment_Check is suppressed, or if
``pragma Restrictions (No_Elaboration_Code)`` is in effect. It is also
suppressed by default on non-strict alignment machines (such as the x86).
diff --git a/gcc/ada/gnat_rm.texi b/gcc/ada/gnat_rm.texi
index 68a3c143dd1..23c9977ed4c 100644
--- a/gcc/ada/gnat_rm.texi
+++ b/gcc/ada/gnat_rm.texi
@@ -19,7 +19,7 @@
@copying
@quotation
-GNAT Reference Manual , Oct 17, 2025
+GNAT Reference Manual , Oct 31, 2025
AdaCore
@@ -20724,8 +20724,7 @@ machines with strict alignment requirements, GNAT
checks (at compile time if possible, generating a warning, or at execution
time with a run-time check) that the alignment is appropriate. If the
run-time check fails, then @code{Program_Error} is raised. This run-time
-check is suppressed if range checks are suppressed, or if the special GNAT
-check Alignment_Check is suppressed, or if
+check is suppressed if the GNAT check Alignment_Check is suppressed, or if
@code{pragma Restrictions (No_Elaboration_Code)} is in effect. It is also
suppressed by default on non-strict alignment machines (such as the x86).
diff --git a/gcc/ada/gnat_ugn.texi b/gcc/ada/gnat_ugn.texi
index 86b2cbc5d3f..478975739f1 100644
--- a/gcc/ada/gnat_ugn.texi
+++ b/gcc/ada/gnat_ugn.texi
@@ -19,7 +19,7 @@
@copying
@quotation
-GNAT User's Guide for Native Platforms , Oct 06, 2025
+GNAT User's Guide for Native Platforms , Oct 31, 2025
AdaCore
@@ -30333,8 +30333,8 @@ to permit their use in free software.
@printindex ge
-@anchor{gnat_ugn/gnat_utility_programs switches-related-to-project-files}@w{
}
@anchor{d2}@w{ }
+@anchor{gnat_ugn/gnat_utility_programs switches-related-to-project-files}@w{
}
@c %**end of body
@bye
diff --git a/gcc/ada/sem_ch13.adb b/gcc/ada/sem_ch13.adb
index 131df3d65d6..31af1bb4675 100644
--- a/gcc/ada/sem_ch13.adb
+++ b/gcc/ada/sem_ch13.adb
@@ -442,11 +442,6 @@ package body Sem_Ch13 is
Off : Boolean;
-- Whether the address is offset within Y in the second case
-
- Alignment_Checks_Suppressed : Boolean;
- -- Whether alignment checks are suppressed by an active scope suppress
- -- setting. We need to save the value in order to be able to reuse it
- -- after the back end has been run.
end record;
package Address_Clause_Checks is new Table.Table (
@@ -457,26 +452,6 @@ package body Sem_Ch13 is
Table_Increment => 200,
Table_Name => "Address_Clause_Checks");
- function Alignment_Checks_Suppressed
- (ACCR : Address_Clause_Check_Record) return Boolean;
- -- Return whether the alignment check generated for the address clause
- -- is suppressed.
-
- ---------------------------------
- -- Alignment_Checks_Suppressed --
- ---------------------------------
-
- function Alignment_Checks_Suppressed
- (ACCR : Address_Clause_Check_Record) return Boolean
- is
- begin
- if Checks_May_Be_Suppressed (ACCR.X) then
- return Is_Check_Suppressed (ACCR.X, Alignment_Check);
- else
- return ACCR.Alignment_Checks_Suppressed;
- end if;
- end Alignment_Checks_Suppressed;
-
-----------------------------------------
-- Adjust_Record_For_Reverse_Bit_Order --
-----------------------------------------
@@ -7086,11 +7061,15 @@ package body Sem_Ch13 is
end if;
end;
- -- Entity has delayed freeze, so we will generate an
+ -- The entity has delayed freeze, so we will generate an
-- alignment check at the freeze point unless suppressed.
+ -- We will unconditionally generate it when the alignment
+ -- is specified in addition to the address, to compensate
+ -- for the check being suppressed by default on machines
+ -- that do not need strict alignment of memory accesses.
- if not Range_Checks_Suppressed (U_Ent)
- and then not Alignment_Checks_Suppressed (U_Ent)
+ if not Alignment_Checks_Suppressed (U_Ent)
+ or else Present (Alignment_Clause (U_Ent))
then
Set_Check_Address_Alignment (N);
end if;
@@ -7165,6 +7144,14 @@ package body Sem_Ch13 is
if Is_Array_Type (U_Ent) then
Set_Alignment (Base_Type (U_Ent), Align);
end if;
+
+ -- See the Attribute_Address case above for the rationale
+
+ if not Is_Type (U_Ent)
+ and then Present (Address_Clause (U_Ent))
+ then
+ Set_Check_Address_Alignment (Address_Clause (U_Ent));
+ end if;
end if;
end Alignment;
@@ -16669,9 +16656,8 @@ package body Sem_Ch13 is
Y : Entity_Id;
Off : Boolean)
is
- ACS : constant Boolean := Scope_Suppress.Suppress (Alignment_Check);
begin
- Address_Clause_Checks.Append ((N, X, A, Y, Off, ACS));
+ Address_Clause_Checks.Append ((N, X, A, Y, Off));
end Register_Address_Clause_Check;
------------------------
@@ -19121,7 +19107,7 @@ package body Sem_Ch13 is
-- Check for known value not multiple of alignment
if No (ACCR.Y) then
- if not Alignment_Checks_Suppressed (ACCR)
+ if Check_Address_Alignment (ACCR.N)
and then X_Alignment /= 0
and then ACCR.A mod X_Alignment /= 0
then
@@ -19166,7 +19152,7 @@ package body Sem_Ch13 is
-- Note: we do not check the alignment if we gave a size
-- warning, since it would likely be redundant.
- elsif not Alignment_Checks_Suppressed (ACCR)
+ elsif Check_Address_Alignment (ACCR.N)
and then Y_Alignment /= Uint_0
and then
(Y_Alignment < X_Alignment
--
2.51.0
