Re: Add VIEW_CONVERT_EXPR to operand_equal_p

[Eric Botcazou <ebotcazou@adacore.com>]

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> Lets go with this patch and hopefully stabilize the tree.  I don't think the
> vector conversions represent an important case.

Unfortunately the patch introduces GIMPLE checking failures in Ada so it will 
need to be completed/improved.  But let's postpone it because we have another 
class of GIMPLE checking failures introduced by the useless_type_conversion_p 
change itself:

c37213j.adb:21:05: warning: variable "X" is read but never assigned
c37213j.adb: In function 'C37213J.PROC.CONSTPROP':
c37213j.adb:41:4: error: invalid conversion in gimple call
struct c37213j__proc__value___PAD

struct c37213j__proc__value___PAD

# .MEM_38 = VDEF <.MEM_37>
MEM[(struct c37213j__proc__value___PAD *)R.12_25] = c37213j.proc.value (); 
[static-chain: &FRAME.39] [return slot optimization]

and:

eric@polaris:~/build/gcc/native> ~/install/gnat-head/bin/gcc -S c37213j.adb -
O2
c37213j.adb:21:05: warning: variable "X" is read but never assigned
c37213j.adb: In function 'C37213J.PROC.VALUE':
c37213j.adb:26:5: error: invalid conversion in return statement
struct c37213j__proc__value___PAD

struct c37213j__proc__value___PAD

# VUSE <.MEM_11>
return _9(D);

What happens here is that GIMPLE statements are remapped through cloning and 
we have a variably-modified type returned by a nested function, so the type of 
the LHS of a GIMPLE_CALL or that of the RHS of a GIMPLE_RETURN is remapped but 
of course not the return type of the function.  This used to be OK because 
remapping is done by means of copy_node and preserves TYPE_CANONICAL, so the 
conversion between remapped and original type was deemed useless; now the 
TYPE_CANONICAL check is gone so the conversion is not useless anymore...

I don't think that we want to introduce an artificial VCE to fix this so we 
probably need a couple of kludges in the GIMPLE verifier instead.

In any case, the more I look into the fallout of the useless_type_conversion_p 
change, the more I find it ill-advised.  We used to have a solid type system 
in the middle-end by means of the predicate and now we have cases for which it 
ought to return false and returns true (e.g. non-structurally equivalent types 
with different calling conventions) and cases for which it can return true and 
returns false (remapped types or types deemed equivalent by the languages).
I don't really know what it was made for, but there must be a better way...


	* gnat.dg/discr45.adb: New test.

-- 
Eric Botcazou

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-- { dg-do run }
-- { dg-options "-O2 -gnatws" }

procedure Discr45 is

  function Ident_Int (I : Integer) return Integer is
  begin
    return I;
  end;

  procedure Proc (Signal : Boolean) is

    subtype Index is Integer range 1..10;

    type My_Arr is array (Index range <>) OF Integer;

    type Rec (D3 : Integer := Ident_Int(1)) is record
      case D3 is
        when -5..10 => C1 : My_Arr(D3..Ident_Int(11));
        when Others => C2 : Integer := Ident_Int(5);
      end case;
    end record;

    X : Rec;

    function Value return Rec;
    pragma No_Inline (Value);

    function Value return Rec is
    begin
      return X;
    end;

  begin
    if X /= Value then
      raise Constraint_Error;
    elsif Signal then
      raise Program_Error;
    end if;
  end;

begin
  Proc (True);
end;