This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: C++ PATCH: PR 16405

Jason Merrill wrote:
On Thu, 23 Dec 2004 00:12:45 -0800, Mark Mitchell <> 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
(916) 791-8304

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]