[gcc r12-2125] [Ada] Optimize away certain elaboration checks

[gcc r12-2125] [Ada] Optimize away certain elaboration checks

[Pierre-Marie de Rodat]

https://gcc.gnu.org/g:29d3965161a8c9337a8b46019eea184ff3a6ac61

commit r12-2125-g29d3965161a8c9337a8b46019eea184ff3a6ac61
Author: Bob Duff <duff@adacore.com>
Date:   Wed May 19 14:24:13 2021 -0400

    [Ada] Optimize away certain elaboration checks
    
    gcc/ada/
    
            * checks.adb (Install_Primitive_Elaboration_Check): Do not
            generate elaboration checks for primitives if pragma Pure or
            Preelaborate is present.  Misc comment fixes, including
            referring to the correct kind of check (elaboration, not
            accessibility).
            * checks.ads, restrict.adb, sem_cat.ads, sinfo.ads: Minor
            reformatting and comment fixes.

Diff:
---
 gcc/ada/checks.adb   | 23 +++++++++++++++--------
 gcc/ada/checks.ads   |  2 +-
 gcc/ada/restrict.adb |  5 ++---
 gcc/ada/sem_cat.ads  |  2 +-
 gcc/ada/sinfo.ads    |  2 +-
 5 files changed, 20 insertions(+), 14 deletions(-)

diff --git a/gcc/ada/checks.adb b/gcc/ada/checks.adb
index 61ce9c22c04..cebeac5ab0c 100644
--- a/gcc/ada/checks.adb
+++ b/gcc/ada/checks.adb
@@ -48,6 +48,7 @@ with Sem;            use Sem;
 with Sem_Aux;        use Sem_Aux;
 with Sem_Ch3;        use Sem_Ch3;
 with Sem_Ch8;        use Sem_Ch8;
+with Sem_Cat;        use Sem_Cat;
 with Sem_Disp;       use Sem_Disp;
 with Sem_Eval;       use Sem_Eval;
 with Sem_Mech;       use Sem_Mech;
@@ -84,7 +85,7 @@ package body Checks is
    --  such as Apply_Scalar_Range_Check that do not insert any code can be
    --  safely called even when the Expander is inactive (but Errors_Detected
    --  is 0). The benefit of executing this code when expansion is off, is
-   --  the ability to emit constraint error warning for static expressions
+   --  the ability to emit constraint error warnings for static expressions
    --  even when we are not generating code.
 
    --  The above is modified in gnatprove mode to ensure that proper check
@@ -8634,7 +8635,7 @@ package body Checks is
          return;
 
       --  Do not generate an elaboration check if the related subprogram is
-      --  not subjected to accessibility checks.
+      --  not subject to elaboration checks.
 
       elsif Elaboration_Checks_Suppressed (Subp_Id) then
          return;
@@ -8644,14 +8645,20 @@ package body Checks is
       elsif Restriction_Active (No_Elaboration_Code) then
          return;
 
+      --  If pragma Pure or Preelaborate applies, then these elaboration checks
+      --  cannot fail, so do not generate them.
+
+      elsif In_Preelaborated_Unit then
+         return;
+
       --  Do not generate an elaboration check if exceptions cannot be used,
       --  caught, or propagated.
 
       elsif not Exceptions_OK then
          return;
 
-      --  Do not consider subprograms which act as compilation units, because
-      --  they cannot be the target of a dispatching call.
+      --  Do not consider subprograms that are compilation units, because they
+      --  cannot be the target of a dispatching call.
 
       elsif Nkind (Context) = N_Compilation_Unit then
          return;
@@ -8681,10 +8688,10 @@ package body Checks is
       elsif Analyzed (Subp_Body) then
          return;
 
-      --  Do not consider primitives which occur within an instance that acts
-      --  as a compilation unit. Such an instance defines its spec and body out
-      --  of order (body is first) within the tree, which causes the reference
-      --  to the elaboration flag to appear as an undefined symbol.
+      --  Do not consider primitives that occur within an instance that is a
+      --  compilation unit. Such an instance defines its spec and body out of
+      --  order (body is first) within the tree, which causes the reference to
+      --  the elaboration flag to appear as an undefined symbol.
 
       elsif Within_Compilation_Unit_Instance (Subp_Id) then
          return;
diff --git a/gcc/ada/checks.ads b/gcc/ada/checks.ads
index 130f871dcdd..a3835d9a4fd 100644
--- a/gcc/ada/checks.ads
+++ b/gcc/ada/checks.ads
@@ -357,7 +357,7 @@ package Checks is
    --  if so inserts the appropriate run-time check.
 
    procedure Install_Primitive_Elaboration_Check (Subp_Body : Node_Id);
-   --  Insert a check which ensures that subprogram body Subp_Body has been
+   --  Insert a check to ensure that subprogram body Subp_Body has been
    --  properly elaborated. The check is installed only when Subp_Body is the
    --  body of a nonabstract library-level primitive of a tagged type. Further
    --  restrictions may apply, see the body for details.
diff --git a/gcc/ada/restrict.adb b/gcc/ada/restrict.adb
index 4f1dea4adef..d97a42eb2f5 100644
--- a/gcc/ada/restrict.adb
+++ b/gcc/ada/restrict.adb
@@ -396,10 +396,9 @@ package body Restrict is
       N : Node_Id;
       V : Uint := Uint_Minus_1)
    is
-      Msg_Issued : Boolean;
-      pragma Unreferenced (Msg_Issued);
+      Ignore_Msg_Issued : Boolean;
    begin
-      Check_Restriction (Msg_Issued, R, N, V);
+      Check_Restriction (Ignore_Msg_Issued, R, N, V);
    end Check_Restriction;
 
    procedure Check_Restriction
diff --git a/gcc/ada/sem_cat.ads b/gcc/ada/sem_cat.ads
index 3fa3339d09b..90a713bd871 100644
--- a/gcc/ada/sem_cat.ads
+++ b/gcc/ada/sem_cat.ads
@@ -27,7 +27,7 @@
 --  the semantic restrictions required for the categorization pragmas:
 --
 --    Preelaborate
---    Pure,
+--    Pure
 --    Remote_Call_Interface
 --    Remote_Types
 --    Shared_Passive
diff --git a/gcc/ada/sinfo.ads b/gcc/ada/sinfo.ads
index 25a61ad5665..71da7fc583e 100644
--- a/gcc/ada/sinfo.ads
+++ b/gcc/ada/sinfo.ads
@@ -2082,7 +2082,7 @@ package Sinfo is
    --    that no elaboration check is needed on the call, because it appears in
    --    the context of a local Suppress pragma. This is used on calls within
    --    task bodies, where the actual elaboration checks are applied after
-   --    analysis, when the local scope stack is not present
+   --    analysis, when the local scope stack is not present.
 
    --  No_Entities_Ref_In_Spec
    --    Present in N_With_Clause nodes. Set if the with clause is on the