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From: Jonathan Wakely <jwakely.gcc@gmail.com>
Date: Mon, 19 Jul 2021 15:08:38 +0100
Message-ID: <CAH6eHdThayp6=UKYrcewkez7FpRgwZ9etQCFBoj=RKfX=zruYw@mail.gmail.com>
Subject: Re: [RFC/PATCH] Use range-based for loops for traversing loops
To: "Kewen.Lin" <linkw@linux.ibm.com>
Cc: GCC Patches <gcc-patches@gcc.gnu.org>, Martin Sebor <msebor@gmail.com>, 
 Richard Biener <richard.guenther@gmail.com>,
 Richard Sandiford <richard.sandiford@arm.com>, 
 Jakub Jelinek <jakub@redhat.com>, Trevor Saunders <tbsaunde@tbsaunde.org>, 
 Segher Boessenkool <segher@kernel.crashing.org>
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On Mon, 19 Jul 2021 at 07:20, Kewen.Lin <linkw@linux.ibm.com> wrote:
>
> Hi,
>
> This patch follows Martin's suggestion here[1], to support
> range-based for loops for traversing loops, analogously to
> the patch for vec[2].
>
> Bootstrapped and regtested on powerpc64le-linux-gnu P9,
> x86_64-redhat-linux and aarch64-linux-gnu, also
> bootstrapped on ppc64le P9 with bootstrap-O3 config.
>
> Any comments are appreciated.

In the loops_list::iterator type, this looks a little strange:

+    bool
+    operator!= (const iterator &rhs) const
+    {
+      return this->curr_idx < rhs.curr_idx;
+    }
+

This works fine when the iterator type is used implicitly in a
range-based for loop, but it wouldn't work for explicit uses of the
iterator type where somebody does the != comparison with the
past-the-end iterator on on the LHS:

auto&& list ALL_LOOPS(foo);
auto end = list.end();
auto begin = list.begin();
while (--end != begin)