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Date: Fri, 06 Mar 2015 21:46:00 -0000
From: Jason Merrill <jason@redhat.com>
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To: Aldy Hernandez <aldyh@redhat.com>, gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [patch] Optimize empty class copies within a C++ return statement
References: <54F8E5D3.4050607@redhat.com> <54F94715.4000208@redhat.com> <54F9D396.3000400@redhat.com>
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On 03/06/2015 11:19 AM, Aldy Hernandez wrote:
> We are hitting the MODIFY_EXPR case.  Indeed, _because_ we hit the
> MODIFY_EXPR is that we return the uninitialized temporary.
>
> For example, we start with:
>
>      return retval = TARGET_EXPR <D.2347, ...>
>
> which becomes:
>
>      <stuff with &D.2347>
>      return D.2349 = D.2347;
>
> which the aforementioned MODIFY_EXPR case turns into:
>
>      <stuff with &D.2347>
>      return D.2349;

But doesn't this still involve a MODIFY_EXPR, i.e. return retval = D.2349?

Jason