[Ada] Fix spurious alignment warning on simple address clause

--- gcc/ada/checks.adb
+++ gcc/ada/checks.adb
@@ -808,7 +808,21 @@  package body Checks is
 
             if Compile_Time_Known_Value (Expr) then
                Alignment_Warnings.Append
-                 ((E => E, A => Expr_Value (Expr), W => Warning_Msg));
+                 ((E => E,
+                   A => Expr_Value (Expr),
+                   P => Empty,
+                   W => Warning_Msg));
+
+            --  Likewise if the expression is of the form X'Address
+
+            elsif Nkind (Expr) = N_Attribute_Reference
+              and then Attribute_Name (Expr) = Name_Address
+            then
+               Alignment_Warnings.Append
+                 ((E => E,
+                   A => No_Uint,
+                   P => Prefix (Expr),
+                   W => Warning_Msg));
 
             --  Add explanation of the warning generated by the check
 
@@ -10925,7 +10939,12 @@  package body Checks is
                     renames Alignment_Warnings.Table (J);
          begin
             if Known_Alignment (AWR.E)
-              and then AWR.A mod Alignment (AWR.E) = 0
+              and then ((AWR.A /= No_Uint
+                          and then AWR.A mod Alignment (AWR.E) = 0)
+                        or else (Present (AWR.P)
+                                  and then Has_Compatible_Alignment
+                                             (AWR.E, AWR.P, True) =
+                                               Known_Compatible))
             then
                Delete_Warning_And_Continuations (AWR.W);
             end if;

--- gcc/ada/checks.ads
+++ gcc/ada/checks.ads
@@ -90,7 +90,7 @@  package Checks is
    --  When we have address clauses, there is an issue of whether the address
    --  specified is appropriate to the alignment. In the general case where the
    --  address is dynamic, we generate a check and a possible warning (this
-   --  warning occurs for example if we have a restricted run time with the
+   --  warning occurs for example if we have a restricted runtime with the
    --  restriction No_Exception_Propagation). We also issue this warning in
    --  the case where the address is static, but we don't know the alignment
    --  at the time we process the address clause. In such a case, we issue the
@@ -98,7 +98,7 @@  package Checks is
    --  annotated the actual alignment chosen) that the warning was not needed.
 
    --  To deal with deleting these potentially annoying warnings, we save the
-   --  warning information in a table, and then delete the waranings in the
+   --  warning information in a table, and then delete the warnings in the
    --  post compilation validation stage if we can tell that the check would
    --  never fail (in general the back end will also optimize away the check
    --  in such cases).
@@ -113,6 +113,9 @@  package Checks is
       --  Compile time known value of address clause for which the alignment
       --  is to be checked once we know the alignment.
 
+      P : Node_Id;
+      --  Prefix of address clause when it is of the form X'Address
+
       W : Error_Msg_Id;
       --  Id of warning message we might delete
    end record;

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/warn31.adb
@@ -0,0 +1,5 @@ 
+--  { dg-do compile }
+--  { dg-options "-gnatw.x -gnatd.a" }
+package body Warn31 is
+    procedure Dummy is null;
+end Warn31;

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/warn31.ads
@@ -0,0 +1,20 @@ 
+pragma Restrictions (No_Exception_Propagation);
+
+package Warn31 is
+
+   type U16 is mod 2 ** 16;
+   type U32 is mod 2 ** 32;
+
+   type Pair is record
+      X, Y : U16;
+   end record;
+   for Pair'Alignment use U32'Alignment;
+
+   Blob : array (1 .. 2) of Pair;
+
+   Sum : array (1 .. 2) of U32;
+   for Sum'Address use Blob'Address;
+
+   procedure Dummy;
+
+end Warn31;
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