[Ada] Fix sharing of expression in array aggregate with others choice
diff mbox series

Message ID 20190918083945.GA145214@adacore.com
State New
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Series
  • [Ada] Fix sharing of expression in array aggregate with others choice
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Commit Message

Pierre-Marie de Rodat Sept. 18, 2019, 8:39 a.m. UTC
This change fixes a long-standing issue in the compiler that is
generally silent but may lead to wrong code generation in specific
circumstances.  When an others choice in an array aggregate spans
multiple ranges, the compiler may generate multiple (groups of)
assignments for the ranges.

The problem is that it internally reuses the original expression for all
the ranges, which is problematic if this expression gets rewritten
during the processing of one of the ranges and typically causes a new
temporary to be shared between different ranges.

The solution is to duplicate the original expression for each range.

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

2019-09-18  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* exp_aggr.adb (Build_Array_Aggr_Code): In STEP 1 (c), duplicate
	the expression and reset the Loop_Actions for each loop
	generated for an others choice.

gcc/testsuite/

	* gnat.dg/aggr28.adb: New testcase.

Patch
diff mbox series

--- gcc/ada/exp_aggr.adb
+++ gcc/ada/exp_aggr.adb
@@ -2075,7 +2075,6 @@  package body Exp_Aggr is
             Choice := First (Choice_List (Assoc));
             while Present (Choice) loop
                if Nkind (Choice) = N_Others_Choice then
-                  Set_Loop_Actions (Assoc, New_List);
                   Others_Assoc := Assoc;
                   exit;
                end if;
@@ -2122,7 +2121,8 @@  package body Exp_Aggr is
 
          if Present (Others_Assoc) then
             declare
-               First : Boolean := True;
+               First    : Boolean := True;
+               Dup_Expr : Node_Id;
 
             begin
                for J in 0 .. Nb_Choices loop
@@ -2160,9 +2160,19 @@  package body Exp_Aggr is
                     or else not Empty_Range (Low, High)
                   then
                      First := False;
+
+                     --  Duplicate the expression in case we will be generating
+                     --  several loops. As a result the expression is no longer
+                     --  shared between the loops and is reevaluated for each
+                     --  such loop.
+
+                     Expr := Get_Assoc_Expr (Others_Assoc);
+                     Dup_Expr := New_Copy_Tree (Expr);
+                     Set_Parent (Dup_Expr, Parent (Expr));
+
+                     Set_Loop_Actions (Others_Assoc, New_List);
                      Append_List
-                       (Gen_Loop (Low, High,
-                          Get_Assoc_Expr (Others_Assoc)), To => New_Code);
+                       (Gen_Loop (Low, High, Dup_Expr), To => New_Code);
                   end if;
                end loop;
             end;

--- /dev/null
new file mode 100644
+++ gcc/testsuite/gnat.dg/aggr28.adb
@@ -0,0 +1,29 @@ 
+--  { dg-do run }
+
+procedure Aggr28 is
+
+  Count : Natural := 0;
+
+  function Get (S: String) return String is
+  begin
+    Count := Count + 1;
+    return S;
+  end;
+
+  Max_Error_Length : constant := 8;
+  subtype Error_Type is String (1 .. Max_Error_Length);
+
+  type Rec is record
+    Text : Error_Type;
+  end record;
+
+  type Arr is array (1 .. 16) of Rec;
+
+  Table : constant Arr :=
+    (3 => (Text => Get ("INVALID ")), others => (Text => Get ("OTHERS  ")));
+
+begin
+  if Count /= Table'Length then
+    raise Program_Error;
+  end if;
+end;
\ No newline at end of file