Re: [wwwdocs] Document in changes.html -fcode-hoisting, -fipa-bit-cp, -fipa-vrp, -fsplit-loops, GCJ removal, x86 ISA additions, -fshrink-wrap-separate etc.

[Prathamesh Kulkarni <prathamesh dot kulkarni at linaro dot org>]

On 27 January 2017 at 22:00, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> This patch attempts to document some new features (without warnings,
> those are partially covered by Marek's patch, C++ FE (would be nice
> to document -faligned-new, -fnew-inheriting-ctors, -fnew-ttp-matching,
> -fstrong-eval-order and what from C++ is supported) and the BRIG FE).
>
> Ok for wwwdocs?
>
> Index: changes.html
> ===================================================================
> RCS file: /cvs/gcc/wwwdocs/htdocs/gcc-7/changes.html,v
> retrieving revision 1.44
> diff -u -p -r1.44 changes.html
> --- changes.html        27 Jan 2017 09:54:32 -0000      1.44
> +++ changes.html        27 Jan 2017 16:23:03 -0000
> @@ -45,8 +45,39 @@ a work-in-progress.</h2>
>    <li>A new store merging pass has been added.  It merges constant stores to
>    adjacent memory locations into fewer, wider, stores.
>    It can be enabled by using the <code>-fstore-merging</code> option and is
> -  enabled by default at <code>-Os</code> and the <code>-O2</code> optimization
> -  level or higher.</li>
> +  enabled by default at the <code>-O2</code> optimization
> +  level or higher (including <code>-Os</code>).</li>
> +
> +  <li>A new code hoisting optimization has been added to the partial
> +  redundancy elimination pass.  It attempts to move evaluation of
> +  expressions executed on all paths to the function exit as early as
> +  possible, which helps primarily for code size, but can be useful for
> +  speed of generated code as well.  It can be enabled by using the
> +  <code>-fcode-hoisting</code> option and is enabled by default at
> +  the <code>-O2</code> optimization level or higher.</li>
> +
> +  <li>A new interprocedural bitwise constant propagation optimization
> +  has been added, which propagates knowledge about which bits of variables
> +  are known to be zero (including pointer alignment information) across
> +  the call graph.  It can be enabled by using the <code>-fipa-bit-cp</code>
> +  option if <code>-fipa-cp</code> is enabled as well, and is enabled by
> +  default at the <code>-O2</code> optimization level and higher.</li>
Hi,
Just a small comment:  -fipa-bit-cp makes -fipa-cp-alignment deprecated.
Sorry for not documenting this option myself and thanks for writing it up!

Regards,
Prathamesh
> +
> +  <li>A new interprocedural value range propagation optimization has been
> +  added, which propagates integral ranges that variable values can be proven
> +  to be within across the call graph.  It can be enabled by using the
> +  <code>-fipa-vrp</code> option and is enabled by default at the
> +  <code>-O2</code> optimization level and higher.</li>
> +
> +  <li>A new loop splitting optimization pass has been added.  It splits
> +  certain loops if they contain a condition that is always true on one
> +  side of the iteration space and always false on the other into two
> +  loops where each of the new two loops iterates just on one of the sides
> +  of the iteration space and the condition does not need to be checked
> +  inside of the loop.  It can be enabled by using the
> +  <code>-fsplit-loops</code> option and is enabled by default at the
> +  <code>-O3</code> optimization level or higher.</li>
> +
>    <li>AddressSanitizer gained a new sanitization option, <code>-fsanitize-address-use-after-scope</code>,
>        which enables sanitization of variables whose address is taken and used after a scope where the
>        variable is defined:
> @@ -64,17 +95,17 @@ main (int argc, char **argv)
>    return *ptr;
>  }
>
> -==28882==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fffb8dba990 at pc 0x0000004006d5 bp 0x7fffb8dba960 sp 0x7fffb8dba958
> -WRITE of size 1 at 0x7fffb8dba990 thread T0
> +<span class="boldred">==28882==ERROR: AddressSanitizer: stack-use-after-scope on address 0x7fffb8dba990 at pc 0x0000004006d5 bp 0x7fffb8dba960 sp 0x7fffb8dba958</span>
> +<span class="boldblue">WRITE of size 1 at 0x7fffb8dba990 thread T0</span>
>      #0 0x4006d4 in main /tmp/use-after-scope-1.c:10
>      #1 0x7f9c71943290 in __libc_start_main (/lib64/libc.so.6+0x20290)
>      #2 0x400739 in _start (/tmp/a.out+0x400739)
>
> -Address 0x7fffb8dba990 is located in stack of thread T0 at offset 32 in frame
> +<span class="boldlime">Address 0x7fffb8dba990 is located in stack of thread T0 at offset 32 in frame</span>
>      #0 0x40067f in main /tmp/use-after-scope-1.c:3
>
>    This frame has 1 object(s):
> -    [32, 33) 'my_char' &lt;== Memory access at offset 32 is inside this variable
> +    [32, 33) 'my_char' <span class="boldlime">&lt;== Memory access at offset 32 is inside this variable</span>
>    </pre></blockquote>
>
>    The option is enabled by default with <code>-fsanitize=address</code> and disabled
> @@ -92,6 +123,16 @@ Address 0x7fffb8dba990 is located in sta
>
>    </li>
>
> +  <li>The <code>-fsanitize=signed-integer-overflow</code> suboption of the
> +  UndefinedBehavior Sanitizer now diagnose arithmetic overflows even on
> +  arithmetic operations with generic vectors.</li>
> +
> +  <li>The upcoming version 5 of the <a
> +  href="http://www.dwarfstd.org/Download.php";>DWARF</a> debugging
> +  information standard is supported through the <code>-gdwarf-5</code>
> +  option.  The DWARF version 4 debugging information remains the
> +  default until debugging information consumers are adjusted.</li>
> +
>  </ul>
>
>  <!-- .................................................................. -->
> @@ -255,6 +296,14 @@ of the global declaration:</p>
>    currently has the value of <code>UINTMAX_MAX</code> on all systems,
>    reflecting that GCC's compile-time conversions are correctly rounded
>    for any number of digits.</li>
> +<li>New <code>__builtin_add_overflow_p</code>,
> +  <code>__builtin_sub_overflow_p</code>,
> +  <code>__builtin_mul_overflow_p</code> built-in functions have been added.
> +  These work similarly to earlier added built-in functions without the
> +  <code>_p</code> suffix, but don't actually store the result of the
> +  arithmetics anywhere, just return whether the operation would overflow.
> +  These builtins allow easy checking for overflows e.g. in C++
> +  <code>constexpr</code> contexts.</li>
>  </ul>
>
>  <h3 id="c">C</h3>
> @@ -291,6 +340,8 @@ of the global declaration:</p>
>    (suffixed <code>f<i>N</i></code> or <code>f<i>N</i>x</code>) for the
>    new
>    types: <code>__builtin_copysign</code>, <code>__builtin_fabs</code>, <code>__builtin_huge_val</code>, <code>__builtin_inf</code>, <code>__builtin_nan</code>, <code>__builtin_nans</code>.</p></li>
> +  <li>Compilation with <code>-fopenmp</code> is now compatible with
> +  C11 <code>_Atomic</code> keyword.</li>
>  </ul>
>
>  <h3 id="cxx">C++</h3>
> @@ -428,11 +479,17 @@ Fortran runtime error: Loop iterates inf
>      </pre></blockquote>
>    </li>
>
> +  <li>Version 4.5 of the <a href="http://www.openmp.org/specifications/";
> +      >OpenMP specification</a> is now partially supported also in the
> +      Fortran compilers, largest missing support in the Fortran frontend
> +      is structure element mapping .</li>
>  </ul>
>
>  <!-- <h3 id="go">Go</h3> -->
>
> -<!-- <h3 id="java">Java (GCJ)</h3> -->
> +<h3 id="java">Java (GCJ)</h3>
> +<p>The GCC Java frontend and associated libjava runtime library have been
> +removed from GCC.</p>
>
>  <!-- .................................................................. -->
>  <h2 id="jit">libgccjit</h2>
> @@ -561,7 +618,13 @@ const int* get_address (unsigned idx)
>
>  <!-- <h3 id="hsa">Heterogeneous Systems Architecture</h3> -->
>
> -<!-- <h3 id="x86">IA-32/x86-64</h3> -->
> +<h3 id="x86">IA-32/x86-64</h3>
> +<ul>
> +  <li>Support for the AVX-512 Fused Multiply Accumulation Packed Single precision
> +  (4FMAPS), AVX-512 Vector Neural Network Instructions Word variable precision
> +  (4VNNIW), AVX-512 Vector Population Count (VPOPCNTDQ) and Software
> +  Guard Extensions (SGX) ISA extensions has been added.</li>
> +</ul>
>
>  <!-- <h3 id="mips">MIPS</h3> -->
>
> @@ -571,12 +634,23 @@ const int* get_address (unsigned idx)
>
>  <!-- <h3 id="nds32">NDS32</h3> -->
>
> +<h3 id="nvptx">NVPTX</h3>
> +<ul>
> +  <li>OpenMP target regions can now be offloaded to NVidia PTX GPGPUs.
> +      See https://gcc.gnu.org/wiki/Offloading on how to configure it.</li>
> +</ul>
> +
>  <h3 id="powerpc">PowerPC / PowerPC64 / RS6000</h3>
>  <ul>
>    <li>The PowerPC port now uses LRA by default.</li>
>    <li>GCC now diagnoses inline assembly that clobbers register r2.
>      This has always been invalid code, and is no longer quietly
>      tolerated.</li>
> +  <li>Shrink-wrapping optimization can now separate portions of
> +    prologues and epilogues to improve performance if some of the
> +    work done traditionally by prologues and epilogues is not needed
> +    on certain paths.  This is controlled by the
> +    <code>-fshrink-wrap-separate</code> option, enabled by default.</li>
>  </ul>
>
>  <!-- <h3 id="s390">S/390, System z, IBM z Systems</h3> -->
>
>         Jakub