PATCH to add -flifetime-dse=1

[Jakub Jelinek]

On Wed, Feb 24, 2016 at 10:15:35AM -0500, Jason Merrill wrote:
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -6809,7 +6809,10 @@ value, and any changes during the lifetime of the object are dead when
>  the object is destroyed.  Normally dead store elimination will take
>  advantage of this; if your code relies on the value of the object
>  storage persisting beyond the lifetime of the object, you can use this
> -flag to disable this optimization.
> +flag to disable this optimization.  To preserve stores before the
> +constructor starts (e.g. because your operator new clears the object
> +storage) but still treat the object as dead after the destructor you,
> +can use -flifetime-dse=1.

That should be @option{-flifetime-dse=1} I think.  Shouldn't -flifetime-dse=
be also in @opindex at the beginning of the paragraph, and documented what
the values mean (0 equivalent of -fno-lifetime-dse (or document it vice
versa) and 2 full lifetime dse enabled?

	Jakub