[Ada] Avoid uninitialized variable in bounded containers

[Pierre-Marie de Rodat <derodat@adacore.com>]

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In function Copy in Ada.Containers.Bounded_Ordered_Sets and other
bounded containers packages, remove a possible use of an uninitialized
variable. This was not a bug, because the uninitialized variable could
be used only if checks are suppressed, and the checks would have failed,
leading to erroneous execution.

However, it seems more robust this way, and is probably equally
efficient, and avoids a warning that is given if checks are suppressed,
and the -Wall switch is given, and optimization is turned on.

Tested on x86_64-pc-linux-gnu, committed on trunk

2019-09-18  Bob Duff  <duff@adacore.com>

gcc/ada/

	* libgnat/a-cbhama.adb, libgnat/a-cbhase.adb,
	libgnat/a-cbmutr.adb, libgnat/a-cborma.adb,
	libgnat/a-cborse.adb, libgnat/a-cobove.adb (Copy): Avoid reading
	the uninitialized variable C in the Checks = False case. Change
	variable to be a constant.

gcc/testsuite/

	* gnat.dg/containers1.adb, gnat.dg/containers1.ads: New
	testcase.

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--- gcc/ada/libgnat/a-cbhama.adb
+++ gcc/ada/libgnat/a-cbhama.adb
@@ -262,18 +262,14 @@ package body Ada.Containers.Bounded_Hashed_Maps is
       Capacity : Count_Type := 0;
       Modulus  : Hash_Type := 0) return Map
    is
-      C : Count_Type;
+      C : constant Count_Type :=
+        (if Capacity = 0 then Source.Length
+         else Capacity);
       M : Hash_Type;
 
    begin
-      if Capacity = 0 then
-         C := Source.Length;
-
-      elsif Capacity >= Source.Length then
-         C := Capacity;
-
-      elsif Checks then
-         raise Capacity_Error with "Capacity value too small";
+      if Checks and then C < Source.Length then
+         raise Capacity_Error with "Capacity too small";
       end if;
 
       if Modulus = 0 then

--- gcc/ada/libgnat/a-cbhase.adb
+++ gcc/ada/libgnat/a-cbhase.adb
@@ -254,16 +254,14 @@ package body Ada.Containers.Bounded_Hashed_Sets is
       Capacity : Count_Type := 0;
       Modulus  : Hash_Type := 0) return Set
    is
-      C : Count_Type;
+      C : constant Count_Type :=
+        (if Capacity = 0 then Source.Length
+         else Capacity);
       M : Hash_Type;
 
    begin
-      if Capacity = 0 then
-         C := Source.Length;
-      elsif Capacity >= Source.Length then
-         C := Capacity;
-      elsif Checks then
-         raise Capacity_Error with "Capacity value too small";
+      if Checks and then C < Source.Length then
+         raise Capacity_Error with "Capacity too small";
       end if;
 
       if Modulus = 0 then

--- gcc/ada/libgnat/a-cbmutr.adb
+++ gcc/ada/libgnat/a-cbmutr.adb
@@ -625,15 +625,12 @@ package body Ada.Containers.Bounded_Multiway_Trees is
      (Source   : Tree;
       Capacity : Count_Type := 0) return Tree
    is
-      C : Count_Type;
-
+      C : constant Count_Type :=
+        (if Capacity = 0 then Source.Count
+         else Capacity);
    begin
-      if Capacity = 0 then
-         C := Source.Count;
-      elsif Capacity >= Source.Count then
-         C := Capacity;
-      elsif Checks then
-         raise Capacity_Error with "Capacity value too small";
+      if Checks and then C < Source.Count then
+         raise Capacity_Error with "Capacity too small";
       end if;
 
       return Target : Tree (Capacity => C) do

--- gcc/ada/libgnat/a-cborma.adb
+++ gcc/ada/libgnat/a-cborma.adb
@@ -464,17 +464,12 @@ package body Ada.Containers.Bounded_Ordered_Maps is
    ----------
 
    function Copy (Source : Map; Capacity : Count_Type := 0) return Map is
-      C : Count_Type;
-
+      C : constant Count_Type :=
+        (if Capacity = 0 then Source.Length
+         else Capacity);
    begin
-      if Capacity = 0 then
-         C := Source.Length;
-
-      elsif Capacity >= Source.Length then
-         C := Capacity;
-
-      elsif Checks then
-         raise Capacity_Error with "Capacity value too small";
+      if Checks and then C < Source.Length then
+         raise Capacity_Error with "Capacity too small";
       end if;
 
       return Target : Map (Capacity => C) do

--- gcc/ada/libgnat/a-cborse.adb
+++ gcc/ada/libgnat/a-cborse.adb
@@ -442,15 +442,12 @@ package body Ada.Containers.Bounded_Ordered_Sets is
    ----------
 
    function Copy (Source : Set; Capacity : Count_Type := 0) return Set is
-      C : Count_Type;
-
+      C : constant Count_Type :=
+        (if Capacity = 0 then Source.Length
+         else Capacity);
    begin
-      if Capacity = 0 then
-         C := Source.Length;
-      elsif Capacity >= Source.Length then
-         C := Capacity;
-      elsif Checks then
-         raise Capacity_Error with "Capacity value too small";
+      if Checks and then C < Source.Length then
+         raise Capacity_Error with "Capacity too small";
       end if;
 
       return Target : Set (Capacity => C) do

--- gcc/ada/libgnat/a-cobove.adb
+++ gcc/ada/libgnat/a-cobove.adb
@@ -451,18 +451,12 @@ package body Ada.Containers.Bounded_Vectors is
      (Source   : Vector;
       Capacity : Count_Type := 0) return Vector
    is
-      C : Count_Type;
-
+      C : constant Count_Type :=
+        (if Capacity = 0 then Source.Length
+         else Capacity);
    begin
-      if Capacity = 0 then
-         C := Source.Length;
-
-      elsif Capacity >= Source.Length then
-         C := Capacity;
-
-      elsif Checks then
-         raise Capacity_Error
-           with "Requested capacity is less than Source length";
+      if Checks and then C < Source.Length then
+         raise Capacity_Error with "Capacity too small";
       end if;
 
       return Target : Vector (C) do

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/containers1.adb
@@ -0,0 +1,5 @@
+--  { dg-do compile }
+--  { dg-options "-Wall -O2" }
+package body Containers1 is
+   procedure Dummy is null;
+end Containers1;

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/containers1.ads
@@ -0,0 +1,6 @@
+with Ada.Containers.Bounded_Ordered_Sets; use Ada.Containers;
+package Containers1 is
+   pragma Suppress (All_Checks);
+   package Sets is new Bounded_Ordered_Sets (Boolean);
+   procedure Dummy;
+end Containers1;
\ No newline at end of file