Ada: fix validity check on some floating point operation

[Arnaud Charlet <charlet@ACT-Europe.FR>]

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Tested on x86-linux

Validity checks were properly enabled on the operands of these operations,
but not on the result, which allowed the generation and propagation of abnormal
values (Infinities and NaN's).
Test p_test_float verifies that invalid values are properly
detected:

with TEXT_IO;
use TEXT_IO;

procedure P_TEST_FLOAT is
  V_1, V_2, V_3 : Long_Float; 
begin
  V_1 := 0.004389773266958945;
  V_2 := 0.0;

  V_3 := V_1 / V_2;
  put_line ("Failed: division by zero");
exception
  when constraint_error => put_line ("division by zero detected");
end P_TEST_FLOAT;

$ gnatmake -q -gnatVirofc p_test_float

2004-10-26  Ed Schonberg  <schonberg@gnat.com>

	* checks.adb (Expr_Known_Valid): If floating-point validity checks are
	enabled, check the result of unary and binary operations when the
	expression is the right-hand side of an assignment.


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Index: checks.adb
===================================================================
RCS file: /cvs/gcc/gcc/gcc/ada/checks.adb,v
retrieving revision 1.29
diff -u -p -r1.29 checks.adb
--- checks.adb	4 Oct 2004 14:58:46 -0000	1.29
+++ checks.adb	27 Oct 2004 09:32:36 -0000
@@ -3792,13 +3792,26 @@ package body Checks is
 
       --  The result of any function call or operator is always considered
       --  valid, since we assume the necessary checks are done by the call.
+      --  For operators on floating-point operations, we must also check
+      --  when the operation is the right-hand side of an assignment, or
+      --  is an actual in a call.
 
-      elsif Nkind (Expr) in N_Binary_Op
-              or else
-            Nkind (Expr) in N_Unary_Op
-              or else
-            Nkind (Expr) = N_Function_Call
+      elsif
+        Nkind (Expr) in N_Binary_Op or else Nkind (Expr) in N_Unary_Op
       then
+         if Is_Floating_Point_Type (Typ)
+            and then Validity_Check_Floating_Point
+            and then
+              (Nkind (Parent (Expr)) = N_Assignment_Statement
+                or else Nkind (Parent (Expr)) = N_Function_Call
+                or else Nkind (Parent (Expr)) = N_Parameter_Association)
+         then
+            return False;
+         else
+            return True;
+         end if;
+
+      elsif Nkind (Expr) = N_Function_Call then
          return True;
 
       --  For all other cases, we do not know the expression is valid