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Fri, 15 Dec 2023 00:06:18 -0800 (PST) MIME-Version: 1.0 References: <202312150123.3BF1NAMM1930388@shliclel4214.sh.intel.com> In-Reply-To: <202312150123.3BF1NAMM1930388@shliclel4214.sh.intel.com> From: Richard Biener Date: Fri, 15 Dec 2023 09:06:07 +0100 Message-ID: Subject: Re: [r14-6559 Regression] FAIL: gcc.dg/guality/pr58791-4.c -Os -DPREVENT_OPTIMIZATION line pr58791-4.c:32 i == 486 on Linux/x86_64 To: "haochen.jiang" Cc: dizhao@os.amperecomputing.com, gcc-regression@gcc.gnu.org, gcc-patches@gcc.gnu.org, haochen.jiang@intel.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,KAM_NUMSUBJECT,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Fri, Dec 15, 2023 at 2:25=E2=80=AFAM haochen.jiang wrote: > > On Linux/x86_64, > > 8afdbcdd7abe1e3c7a81e07f34c256e7f2dbc652 is the first bad commit > commit 8afdbcdd7abe1e3c7a81e07f34c256e7f2dbc652 > Author: Di Zhao > Date: Fri Dec 15 03:22:32 2023 +0800 > > Consider fully pipelined FMA in get_reassociation_width > > caused > > FAIL: gcc.dg/guality/pr58791-4.c -O2 -DPREVENT_OPTIMIZATION line pr58= 791-4.c:32 i2 =3D=3D 487 > FAIL: gcc.dg/guality/pr58791-4.c -O2 -DPREVENT_OPTIMIZATION line pr58= 791-4.c:32 i =3D=3D 486 > FAIL: gcc.dg/guality/pr58791-4.c -O2 -flto -fno-use-linker-plugin -flto= -partition=3Dnone -DPREVENT_OPTIMIZATION line pr58791-4.c:32 i2 =3D=3D 487 > FAIL: gcc.dg/guality/pr58791-4.c -O2 -flto -fno-use-linker-plugin -flto= -partition=3Dnone -DPREVENT_OPTIMIZATION line pr58791-4.c:32 i =3D=3D 486 > FAIL: gcc.dg/guality/pr58791-4.c -O2 -flto -fuse-linker-plugin -fno-fat= -lto-objects -DPREVENT_OPTIMIZATION line pr58791-4.c:32 i2 =3D=3D 487 > FAIL: gcc.dg/guality/pr58791-4.c -O2 -flto -fuse-linker-plugin -fno-fat= -lto-objects -DPREVENT_OPTIMIZATION line pr58791-4.c:32 i =3D=3D 486 > FAIL: gcc.dg/guality/pr58791-4.c -O3 -g -DPREVENT_OPTIMIZATION line p= r58791-4.c:32 i2 =3D=3D 487 > FAIL: gcc.dg/guality/pr58791-4.c -O3 -g -DPREVENT_OPTIMIZATION line p= r58791-4.c:32 i =3D=3D 486 > FAIL: gcc.dg/guality/pr58791-4.c -Os -DPREVENT_OPTIMIZATION line pr58= 791-4.c:32 i2 =3D=3D 487 > FAIL: gcc.dg/guality/pr58791-4.c -Os -DPREVENT_OPTIMIZATION line pr58= 791-4.c:32 i =3D=3D 486 > > with GCC configured with > > ../../gcc/configure --prefix=3D/export/users/haochenj/src/gcc-bisect/mast= er/master/r14-6559/usr --enable-clocale=3Dgnu --with-system-zlib --with-dem= angler-in-ld --with-fpmath=3Dsse --enable-languages=3Dc,c++,fortran --enabl= e-cet --without-isl --enable-libmpx x86_64-linux --disable-bootstrap > > To reproduce: > > $ cd {build_dir}/gcc && make check RUNTESTFLAGS=3D"guality.exp=3Dgcc.dg/g= uality/pr58791-4.c --target_board=3D'unix{-m64\ -march=3Dcascadelake}'" There's an extra intermediate stmt inserted (for much later use, but reassoc inserts close to defs) that is then also used for FMA forming. This disturbs things in some way: g_5 =3D (double) f_4; # DEBUG g =3D> g_5 # DEBUG BEGIN_STMT h_7 =3D (double) b_6(D); # DEBUG h =3D> h_7 # DEBUG BEGIN_STMT _39 =3D h_7 * 3.25e+0; # DEBUG D#5 =3D> g_5 * h_7 # DEBUG i =3D> D#5 # DEBUG BEGIN_STMT # DEBUG i2 =3D> D#5 + 1.0e+0 # DEBUG BEGIN_STMT # DEBUG D#8 =3D> g_5 * _39 _3 =3D .FMA (g_5, _39, h_7); g_5 is dead after the FMA. Interestingly removing the asm volatile (NOP : : : "memory"); asm volatile (NOP : : : "memory"); lines fixes the regression because then we can TER the FMA, keeping g_5 live for longer. Richard.