[Ada] Optimization loses exception in improper use of 'Value

This patch prevents an improper removal of an evaluation of attribute
'Value on an illegal input that will raise Constraint_Error, when a
subsequent use of this evaluation might be optimized away by the
back-end.

2019-07-22  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* libgnat/s-valboo.ads, libgnat/s-valcha.ads,
	libgnat/s-valdec.ads, libgnat/s-valenu.ads,
	libgnat/s-valint.ads, libgnat/s-vallld.ads,
	libgnat/s-vallli.ads, libgnat/s-valllu.ads,
	libgnat/s-valrea.ads, libgnat/s-valuns.ads,
	libgnat/s-valwch.ads: Change categorization of packages that
	implement attribute 'Value from Pure to Preelaborate, to prevent
	undesirable optimizations when the evaluation of the attribute
	raises Constraint_Error, but subsequent use of the result of
	this evsaluation is removed by a subsequent optimization.

gcc/testsuite/

	* gnat.dg/opt80.adb: New testcase.

From-SVN: r273687

gcc/ada/ChangeLog

 2019-07-22  Ed Schonberg  <schonberg@adacore.com>
 
+	* libgnat/s-valboo.ads, libgnat/s-valcha.ads,
+	libgnat/s-valdec.ads, libgnat/s-valenu.ads,
+	libgnat/s-valint.ads, libgnat/s-vallld.ads,
+	libgnat/s-vallli.ads, libgnat/s-valllu.ads,
+	libgnat/s-valrea.ads, libgnat/s-valuns.ads,
+	libgnat/s-valwch.ads: Change categorization of packages that
+	implement attribute 'Value from Pure to Preelaborate, to prevent
+	undesirable optimizations when the evaluation of the attribute
+	raises Constraint_Error, but subsequent use of the result of
+	this evsaluation is removed by a subsequent optimization.
+
+2019-07-22  Ed Schonberg  <schonberg@adacore.com>
+
 	* sem_warn.adb (Check_References): Do not emit s warning on a
 	referenced entity with no explicit assignment if the type of the
 	entity has Preelaborable_Initialixation, such as

gcc/ada/libgnat/s-valboo.ads

@@ -30,7 +30,7 @@
 ------------------------------------------------------------------------------
 
 package System.Val_Bool is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Value_Boolean (Str : String) return Boolean;
    --  Computes Boolean'Value (Str)

gcc/ada/libgnat/s-valcha.ads

@@ -30,7 +30,7 @@
 ------------------------------------------------------------------------------
 
 package System.Val_Char is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Value_Character (Str : String) return Character;
    --  Computes Character'Value (Str)

gcc/ada/libgnat/s-valdec.ads

@@ -34,7 +34,7 @@
 --  Decimal_IO, and the Value attribute for such decimal types.
 
 package System.Val_Dec is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Scan_Decimal
      (Str   : String;

gcc/ada/libgnat/s-valenu.ads

@@ -34,7 +34,7 @@
 --  details of the format of constructed image tables.
 
 package System.Val_Enum is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Value_Enumeration_8
      (Names   : String;

gcc/ada/libgnat/s-valint.ads

@@ -33,7 +33,7 @@
 --  in Text_IO.Integer_IO, and the Value attribute.
 
 package System.Val_Int is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Scan_Integer
      (Str : String;

gcc/ada/libgnat/s-vallld.ads

@@ -34,7 +34,7 @@
 --  Decimal_IO, and the Value attribute for such decimal types.
 
 package System.Val_LLD is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Scan_Long_Long_Decimal
      (Str   : String;

gcc/ada/libgnat/s-vallli.ads

@@ -33,7 +33,7 @@
 --  values for use in Text_IO.Integer_IO, and the Value attribute.
 
 package System.Val_LLI is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Scan_Long_Long_Integer
      (Str  : String;

gcc/ada/libgnat/s-valllu.ads

@@ -35,7 +35,7 @@
 with System.Unsigned_Types;
 
 package System.Val_LLU is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Scan_Raw_Long_Long_Unsigned
      (Str : String;

gcc/ada/libgnat/s-valrea.ads

@@ -30,7 +30,7 @@
 ------------------------------------------------------------------------------
 
 package System.Val_Real is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Scan_Real
      (Str : String;

gcc/ada/libgnat/s-valuns.ads

@@ -35,7 +35,7 @@
 with System.Unsigned_Types;
 
 package System.Val_Uns is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Scan_Raw_Unsigned
      (Str : String;

gcc/ada/libgnat/s-valwch.ads

@@ -34,7 +34,7 @@
 with System.WCh_Con;
 
 package System.Val_WChar is
-   pragma Pure;
+   pragma Preelaborate;
 
    function Value_Wide_Character
      (Str : String;

gcc/testsuite/ChangeLog

 2019-07-22  Ed Schonberg  <schonberg@adacore.com>
 
+	* gnat.dg/opt80.adb: New testcase.
+
+2019-07-22  Ed Schonberg  <schonberg@adacore.com>
+
 	* gnat.dg/warn25.adb: New testcase.
 
 2019-07-22  Yannick Moy  <moy@adacore.com>

gcc/testsuite/gnat.dg/opt80.adb

+--  { dg-do run }
+--  { dg-options "-O2" }
+
+with Ada.Text_IO; use Ada.Text_IO;
+
+procedure Opt80 is
+   Item : Integer;
+begin
+   Item := Integer'Value ("zzz");
+   Put_Line (Boolean'Image (Item'Valid));
+   raise Program_Error;
+exception
+   when Constraint_Error =>
+      null;
+end;