[Ada] Fix biased integer arithmetic

[Ada] Fix biased integer arithmetic

[Eric Botcazou]

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The Ada compiler uses a biased representation when a size clause reserves 
fewer bits than normal either for the lower or for the upper bound.

Tested on x86-64/Linux, applied on the mainline, 10 and 9 branches.


2020-11-11  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc-interface/trans.c (build_binary_op_trapv): Convert operands
	to the result type before doing generic overflow checking.


2020-11-11  Eric Botcazou  <ebotcazou@adacore.com>

	* gnat.dg/bias2.adb: New test.

-- 
Eric Botcazou

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-- { dg-do run }

procedure Bias2 is

  type Biased_T is range 1 .. 2 ** 6;
  for Biased_T'Size use 6;  --  { dg-warning "biased representation" }
  X, Y : Biased_T;

begin
  X := 1;
  Y := 1;
  if X + Y /= 2 then
    raise Program_Error;
  end if;

  X := 2;
  Y := 1;
  if X - Y /= 1 then
    raise Program_Error;
  end if;

  X := 2;
  Y := 3;
  if X * Y /= 6 then
    raise Program_Error;
  end if;

  X := 24;
  Y := 3;
  if X / Y /= 8 then
    raise Program_Error;
  end if;
end;

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diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
index 065fcd2f956..7be8463d32b 100644
--- a/gcc/ada/gcc-interface/trans.c
+++ b/gcc/ada/gcc-interface/trans.c
@@ -9361,6 +9361,11 @@ build_binary_op_trapv (enum tree_code code, tree gnu_type, tree left,
   /* If no operand is a constant, we use the generic implementation.  */
   if (TREE_CODE (lhs) != INTEGER_CST && TREE_CODE (rhs) != INTEGER_CST)
     {
+      /* First convert the operands to the result type like build_binary_op.
+	 This is where the bias is made explicit for biased types.  */
+      lhs = convert (gnu_type, lhs);
+      rhs = convert (gnu_type, rhs);
+
       /* Never inline a 64-bit mult for a 32-bit target, it's way too long.  */
       if (code == MULT_EXPR && precision == 64 && BITS_PER_WORD < 64)
 	{