Re: [PATCH] match.pd: Fix up 1 / X for unsigned X optimization [PR104280]

[Eric Botcazou <botcazou@adacore.com>]

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> Unfortunately this breaks quite a lot of things.

Right, for example in Ada where we now happily turn a division by zero, which 
should raise an exception with -gnatp, into nonsense.  Do we really need this 
rather useless optimization in GCC?  Blindly mimicing LLVM is not a reason...

I have installed the attached testcase, which now fails because of the change.

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

-- 
Eric Botcazou

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-- { dg-do run }

-- This test requires architecture- and OS-specific support code for unwinding
-- through signal frames (typically located in *-unwind.h) to pass.  Feel free
-- to disable it if this code hasn't been implemented yet.

procedure Div_Zero is

  pragma Suppress (All_Checks);

  function Zero return Integer is
  begin
    return 0;
  end;

  D : Integer := Zero;

begin
  D := 1 / D;
  raise Program_Error;
exception
  when Constraint_Error => null;
end;