[COMMITED] ada: Incorrect inferences drawn from if/elsif/while conditions with -gnatVo

[COMMITED] ada: Incorrect inferences drawn from if/elsif/while conditions with -gnatVo

[Marc Poulhiès]

From: Steve Baird <baird@adacore.com>

Within the first (respectively, second) statement list of this if statement
  declare
     X : constant Integer := ... ;
  begin
     if X > 0 then
       ...;
     else
       ...;
     end if;
  end;
we can safely assume that X is greater (respectively, not greater) than 0.

Fix a bug that incorrectly computed the region in which such assumptions
can be made to include the condition of the if-statement. This bug usually
had no effect because semantic analysis/simplification of the condition was
already complete before the code containing the bug was executed.
Unfortunately, this is not true in some cases involving -gnatVo validity
checking. In these cases, the bug could result in incorrect simplification
of the condition at compile time. This, in turn, could lead to incorrect
unconditional execution of one arm of the if-statement at run time. Similar
errors appear to be possible for the conditions of an elsif or a while loop;
the fix addresses these cases as well, although corresponding problems with
these constructs have not been demonstrated.

gcc/ada/

	* exp_util.adb
	(Get_Current_Value_Condition): Treat references occurring within
	the condition of an if statement, an elsif, or a while loop in the
	same way as references that occur before the start of that
	enclosing construct.

Tested on x86_64-pc-linux-gnu, committed on master.

---
 gcc/ada/exp_util.adb | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/gcc/ada/exp_util.adb b/gcc/ada/exp_util.adb
index 61395adf195..f569d2ef583 100644
--- a/gcc/ada/exp_util.adb
+++ b/gcc/ada/exp_util.adb
@@ -6923,6 +6923,11 @@ package body Exp_Util is
             if Loc < Sloc (CV) then
                return;
 
+            --  In condition of IF statement
+
+            elsif In_Subtree (N => Var, Root => Condition (CV)) then
+               return;
+
             --  After end of IF statement
 
             elsif Loc >= Sloc (CV) + Text_Ptr (UI_To_Int (End_Span (CV))) then
@@ -7009,7 +7014,12 @@ package body Exp_Util is
             if Loc < Sloc (CV) then
                return;
 
-               --  After end of IF statement
+            --  In condition of ELSIF part
+
+            elsif In_Subtree (N => Var, Root => Condition (CV)) then
+               return;
+
+            --  After end of IF statement
 
             elsif Loc >= Sloc (Stm) +
               Text_Ptr (UI_To_Int (End_Span (Stm)))
@@ -7066,6 +7076,11 @@ package body Exp_Util is
                if Loc < Sloc (Loop_Stmt) then
                   return;
 
+               --  In condition of while loop
+
+               elsif In_Subtree (N => Var, Root => Condition (CV)) then
+                  return;
+
                --  After end of LOOP statement
 
                elsif Loc >= Sloc (End_Label (Loop_Stmt)) then
-- 
2.34.1