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Tue, 16 Jan 2024 23:56:46 -0800 (PST) MIME-Version: 1.0 References: <20240116221914.267015-1-gkm@rivosinc.com> In-Reply-To: <20240116221914.267015-1-gkm@rivosinc.com> From: YunQiang Su Date: Wed, 17 Jan 2024 15:56:35 +0800 Message-ID: Subject: Re: [PATCH] combine: Don't optimize SIGN_EXTEND of MEM on WORD_REGISTER_OPERATIONS targets [PR113010] To: Greg McGary Cc: gcc-patches@gcc.gnu.org, Greg McGary Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-6.3 required=5.0 tests=BAYES_00,BODY_8BITS,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Greg McGary =E4=BA=8E2024=E5=B9=B41=E6=9C=8817=E6=97=A5= =E5=91=A8=E4=B8=89 06:20=E5=86=99=E9=81=93=EF=BC=9A > > The sign bit of a sign-extending load cannot be known until runtime, > so don't attempt to simplify it in the combiner. > > 2024-01-11 Greg McGary > > PR rtl-optimization/113010 > * combine.cc (expand_compound_operation): Don't simplify > SIGN_EXTEND of a MEM on WORD_REGISTER_OPERATIONS targets > > * gcc.c-torture/execute/pr113010.c: New test. > --- > gcc/combine.cc | 5 +++++ > gcc/testsuite/gcc.c-torture/execute/pr113010.c | 9 +++++++++ > 2 files changed, 14 insertions(+) > create mode 100644 gcc/testsuite/gcc.c-torture/execute/pr113010.c > > diff --git a/gcc/combine.cc b/gcc/combine.cc > index 812553c091e..ba587184dfc 100644 > --- a/gcc/combine.cc > +++ b/gcc/combine.cc > @@ -7208,6 +7208,11 @@ expand_compound_operation (rtx x) > if (len =3D=3D 0) > return x; > > + /* Sign-extending loads can never be simplified at compile time. = */ > + if (WORD_REGISTER_OPERATIONS && MEM_P (XEXP (x, 0)) > + && load_extend_op (inner_mode) =3D=3D SIGN_EXTEND) > + return x; > + > break; > > case ZERO_EXTRACT: > diff --git a/gcc/testsuite/gcc.c-torture/execute/pr113010.c b/gcc/testsui= te/gcc.c-torture/execute/pr113010.c > new file mode 100644 > index 00000000000..a95c613c1df > --- /dev/null > +++ b/gcc/testsuite/gcc.c-torture/execute/pr113010.c > @@ -0,0 +1,9 @@ > +int minus_1 =3D -1; > + > +int > +main () > +{ > + if ((0, 0xfffffffful) >=3D minus_1) There is a warning option: -Wsign-compare Warn when a comparison between signed and unsigned values could produce an incorrect result when the signed value is converted to unsigned. > + __builtin_abort (); > + return 0; > +} > -- > 2.34.1 > --=20 YunQiang Su