Re: C++ PATCH: PR 16405

[Mark Mitchell <mark at codesourcery dot com>]

Jason Merrill wrote:
> On Thu, 23 Dec 2004 00:12:45 -0800, Mark Mitchell <mark@codesourcery.com> wrote:
>
>
> > This patch fixes a C++ optimization problem.  In the case of the code
> > in the attached test case, the compiler was generating a temporary for
> > "a + b", as expected.  Then, for the call to the (implicitly declared)
> > assignment operator "T::operator=", we generated another temporary, to
> > bind to the const reference parameter to the assignment operator.
> > That's permitted, but silly.
> >
> > The problem was that the front-end generates:
> >
> >  memcpy (&a, *(const T*)&<target_expr operator+(b, c)>, sizeof (T))
> >
> > The gimplifier could not see through the INDIRECT_REF/ADDR_EXPR
> > combination to find the underlying TARGET_EXPR, and so generate a
> > temporary for it.
>
>
> I don't see where the second temporary you mention is coming from.  I would
> expect the gimplifier to generate a temporary to store the address of the
> TARGET_EXPR temporary, but that's just a scalar.

Tthe result of operator+ is a class object, not a scalar.  The 
TARGET_EXPR contains the result of the call to operator+.

--
Mark Mitchell
CodeSourcery, LLC
mark@codesourcery.com
(916) 791-8304