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[COMMITTED,13/31] ada: Remove useless trampolines caused by Unchecked_Conversion

Message ID 20240521073035.314024-13-poulhies@adacore.com
State New
Headers show
Series [COMMITTED,01/31] ada: Add new Mingw task priority mapping | expand

Commit Message

Marc Poulhiès May 21, 2024, 7:30 a.m. UTC 
From: Eric Botcazou <ebotcazou@adacore.com>

The partial solution implemented in Validate_Unchecked_Conversion to support
unchecked conversions between addresses and pointers to subprograms, for the
platforms where pointers to subprograms do not all have the same size, turns
out to be counter-productive for others because it may cause the creation of
useless trampolines, which in turn makes the stack executable.

gcc/ada/

	* sem_ch13.adb (Validate_Unchecked_Conversion): Restrict forcing the
	Can_Use_Internal_Rep flag to platforms that require unnesting.

Tested on x86_64-pc-linux-gnu, committed on master.

---
 gcc/ada/sem_ch13.adb | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)
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Patch

diff --git a/gcc/ada/sem_ch13.adb b/gcc/ada/sem_ch13.adb
index 59c80022c20..4cf6fc9a645 100644
--- a/gcc/ada/sem_ch13.adb
+++ b/gcc/ada/sem_ch13.adb
@@ -18132,20 +18132,23 @@  package body Sem_Ch13 is
          Set_No_Strict_Aliasing (Implementation_Base_Type (Target));
       end if;
 
-      --  If the unchecked conversion is between Address and an access
-      --  subprogram type, show that we shouldn't use an internal
-      --  representation for the access subprogram type.
+      --  For code generators that do not support nested subprograms, if the
+      --  unchecked conversion is between Address and an access subprogram
+      --  type, show that we shouldn't use an internal representation for the
+      --  access subprogram type.
 
-      if Is_Access_Subprogram_Type (Target)
-        and then Is_Descendant_Of_Address (Source)
-        and then In_Same_Source_Unit (Target, N)
-      then
-         Set_Can_Use_Internal_Rep (Base_Type (Target), False);
-      elsif Is_Access_Subprogram_Type (Source)
-        and then Is_Descendant_Of_Address (Target)
-        and then In_Same_Source_Unit (Source, N)
-      then
-         Set_Can_Use_Internal_Rep (Base_Type (Source), False);
+      if Unnest_Subprogram_Mode then
+         if Is_Access_Subprogram_Type (Target)
+           and then Is_Descendant_Of_Address (Source)
+           and then In_Same_Source_Unit (Target, N)
+         then
+            Set_Can_Use_Internal_Rep (Base_Type (Target), False);
+         elsif Is_Access_Subprogram_Type (Source)
+           and then Is_Descendant_Of_Address (Target)
+           and then In_Same_Source_Unit (Source, N)
+         then
+            Set_Can_Use_Internal_Rep (Base_Type (Source), False);
+         end if;
       end if;
 
       --  Generate N_Validate_Unchecked_Conversion node for back end in case