C++ PATCH: PR 16405

[Mark Mitchell]

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