From: Eric Botcazou <ebotca...@adacore.com>
This was initially implemented as part of AI12-001 but immediately disabled
because it breaks Florist on 32-bit platforms. However, it is possible to
reenable it in almost all cases without affecting Florist, and the -gnatd_l
switch can now be used to disable it again.
gcc/ada/
* debug.adb (d_l): Document new usage for the compiler.
* freeze.adb (Check_Strict_Alignment): Set the Strict_Alignment
flag on array types with aliased component, except if the
component size is equal to the storage unit or the -gnatd_l switch
is specified.
Tested on x86_64-pc-linux-gnu, committed on master.
---
gcc/ada/debug.adb | 5 ++++-
gcc/ada/freeze.adb | 30 ++++++++++++++++++------------
2 files changed, 22 insertions(+), 13 deletions(-)
diff --git a/gcc/ada/debug.adb b/gcc/ada/debug.adb
index 97f88b7664f..f7fcd399769 100644
--- a/gcc/ada/debug.adb
+++ b/gcc/ada/debug.adb
@@ -148,7 +148,7 @@ package body Debug is
-- d_i Ignore activations and calls to instances for elaboration
-- d_j Read JSON files and populate Repinfo tables (opposite of -gnatRjs)
-- d_k In CodePeer mode disable expansion of assertion checks
- -- d_l
+ -- d_l Disable strict alignment of array types with aliased component
-- d_m
-- d_n
-- d_o
@@ -989,6 +989,9 @@ package body Debug is
-- enabled, expansion of assertion expressions is controlled by
-- pragma Assertion_Policy.
+ -- d_l The compiler does not enforce the strict alignment of array types
+ -- that are declared with an aliased component.
+
-- d_p The compiler ignores calls to subprograms which verify the run-time
-- semantics of invariants and postconditions in both the static and
-- dynamic elaboration models.
diff --git a/gcc/ada/freeze.adb b/gcc/ada/freeze.adb
index d0dd1de087d..3c3d038c392 100644
--- a/gcc/ada/freeze.adb
+++ b/gcc/ada/freeze.adb
@@ -2374,18 +2374,24 @@ package body Freeze is
elsif Is_Array_Type (E) then
Set_Strict_Alignment (E, Strict_Alignment (Component_Type (E)));
- -- ??? AI12-001: Any component of a packed type that contains an
- -- aliased part must be aligned according to the alignment of its
- -- subtype (RM 13.2(7)). This means that the following test:
-
- -- if Has_Aliased_Components (E) then
- -- Set_Strict_Alignment (E);
- -- end if;
-
- -- should be implemented here. Unfortunately it would break Florist,
- -- which has the bad habit of overaligning all the types it declares
- -- on 32-bit platforms. Other legacy codebases could also be affected
- -- because this check has historically been missing in GNAT.
+ -- RM 13.2(7.1/4): Any component of a packed type that contains an
+ -- aliased part shall be aligned according to the alignment of its
+ -- subtype.
+
+ -- Unfortunately this breaks Florist, which has had the bad habit
+ -- of overaligning all the types it declares on 32-bit platforms,
+ -- so make an exception if the component size is the storage unit.
+
+ -- Other legacy codebases could also be affected because this was
+ -- historically not enforced, so -gnatd_l can be used to disable it.
+
+ if Has_Aliased_Components (E)
+ and then not (Known_Component_Size (E)
+ and then Component_Size (E) = System_Storage_Unit)
+ and then not Debug_Flag_Underscore_L
+ then
+ Set_Strict_Alignment (E);
+ end if;
elsif Is_Record_Type (E) then
Comp := First_Component (E);
--
2.45.1
