[Ada] Fix incorrect operand sharing after expansion

[Pierre-Marie de Rodat]

The Expand_N_Op_Expon procedure of the expander starts by relocating its
operands, but later reuses the original right operand in the code
generated in the modular case and, in particular, passes it to
Duplicate_Subexpr, which is fooled into thinking that operands are not
syntactical and thus does not copy them, resulting in sharing.

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

2020-06-17  Eric Botcazou  <ebotca...@adacore.com>

gcc/ada/

        * exp_ch4.adb (Expand_N_Op_Expon): Replace all occurrences of
        the original right operand with the relocated version.
--- gcc/ada/exp_ch4.adb
+++ gcc/ada/exp_ch4.adb
@@ -8778,8 +8778,7 @@ package body Exp_Ch4 is
 
                --  Determine range to see if it can be larger than MaxS
 
-               Determine_Range
-                 (Right_Opnd (N), OK, Lo, Hi, Assume_Valid => True);
+               Determine_Range (Exp, OK, Lo, Hi, Assume_Valid => True);
                TestS := (not OK) or else Hi > MaxS;
 
                --  Signed integer case
@@ -8796,7 +8795,7 @@ package body Exp_Ch4 is
                        Make_Raise_Constraint_Error (Loc,
                          Condition =>
                            Make_Op_Gt (Loc,
-                             Left_Opnd  => Duplicate_Subexpr (Right_Opnd (N)),
+                             Left_Opnd  => Duplicate_Subexpr (Exp),
                              Right_Opnd => Make_Integer_Literal (Loc, MaxS)),
                          Reason    => CE_Overflow_Check_Failed));
                   end if;
@@ -8806,7 +8805,7 @@ package body Exp_Ch4 is
                   Rewrite (N,
                     Make_Op_Shift_Left (Loc,
                       Left_Opnd  => Make_Integer_Literal (Loc, Uint_1),
-                      Right_Opnd => Right_Opnd (N)));
+                      Right_Opnd => Exp));
 
                --  Modular integer case
 
@@ -8824,7 +8823,7 @@ package body Exp_Ch4 is
 
                      Test_Gt :=
                        Make_Op_Gt (Loc,
-                         Left_Opnd  => Duplicate_Subexpr (Right_Opnd (N)),
+                         Left_Opnd  => Duplicate_Subexpr (Exp),
                          Right_Opnd => Make_Integer_Literal (Loc, MaxS));
 
                      Rewrite (N,
@@ -8834,7 +8833,7 @@ package body Exp_Ch4 is
                            Make_Integer_Literal (Loc, Uint_0),
                            Make_Op_Shift_Left (Loc,
                              Left_Opnd  => Make_Integer_Literal (Loc, Uint_1),
-                             Right_Opnd => Right_Opnd (N)))));
+                             Right_Opnd => Exp))));
 
                   --  If we know shift count cannot be greater than MaxS, then
                   --  it is safe to just rewrite as a shift with no test.
@@ -8843,7 +8842,7 @@ package body Exp_Ch4 is
                      Rewrite (N,
                        Make_Op_Shift_Left (Loc,
                          Left_Opnd  => Make_Integer_Literal (Loc, Uint_1),
-                         Right_Opnd => Right_Opnd (N)));
+                         Right_Opnd => Exp));
                   end if;
                end if;