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[176.184.15.56]) by smtp.gmail.com with ESMTPSA id h12-20020aa7c94c000000b00528922bb53bsm5786887edt.76.2023.08.29.08.53.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 29 Aug 2023 08:53:25 -0700 (PDT) Message-ID: <02cd3850-49f4-7a0c-7f92-2461582dabc1@linaro.org> Date: Tue, 29 Aug 2023 17:53:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.14.0 Subject: Re: [PATCH] target/arm: Use deposit_z() in BCF opcode Content-Language: en-US To: Peter Maydell Cc: qemu-devel@nongnu.org, qemu-arm@nongnu.org References: <20230822095156.39868-1-philmd@linaro.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::12f; envelope-from=philmd@linaro.org; helo=mail-lf1-x12f.google.com X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-1.242, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 29/8/23 15:20, Peter Maydell wrote: > On Tue, 22 Aug 2023 at 10:51, Philippe Mathieu-Daudé wrote: >> >> When clearing a bitfield we don't need to lead the > > "load" ? > >> source register. Use deposit_z_i32() with the BFC >> opcode to save a load_reg() call. >> >> Signed-off-by: Philippe Mathieu-Daudé >> --- >> target/arm/tcg/translate.c | 9 ++++----- >> 1 file changed, 4 insertions(+), 5 deletions(-) >> >> diff --git a/target/arm/tcg/translate.c b/target/arm/tcg/translate.c >> index b71ac2d0d5..1a6938d1b3 100644 >> --- a/target/arm/tcg/translate.c >> +++ b/target/arm/tcg/translate.c >> @@ -7255,7 +7255,7 @@ static bool trans_UBFX(DisasContext *s, arg_UBFX *a) >> static bool trans_BFCI(DisasContext *s, arg_BFCI *a) >> { >> int msb = a->msb, lsb = a->lsb; >> - TCGv_i32 t_in, t_rd; >> + TCGv_i32 t_rd; >> int width; >> >> if (!ENABLE_ARCH_6T2) { >> @@ -7268,15 +7268,14 @@ static bool trans_BFCI(DisasContext *s, arg_BFCI *a) >> } >> >> width = msb + 1 - lsb; >> + t_rd = load_reg(s, a->rd); >> if (a->rn == 15) { >> /* BFC */ >> - t_in = tcg_constant_i32(0); >> + tcg_gen_deposit_z_i32(t_rd, t_rd, lsb, width); >> } else { >> /* BFI */ >> - t_in = load_reg(s, a->rn); >> + tcg_gen_deposit_i32(t_rd, t_rd, load_reg(s, a->rn), lsb, width); >> } >> - t_rd = load_reg(s, a->rd); >> - tcg_gen_deposit_i32(t_rd, t_rd, t_in, lsb, width); >> store_reg(s, a->rd, t_rd); >> return true; > > The comment says we are saving a load_reg() call, but the > code change doesn't seem to do that. Before the change: > * for BFC we call load_reg for rd > * for BFI we call load_reg for rn and rd > > After the change: > * for BFC we call load_reg for rd > * for BFI we call load_reg for rn and rd > > So we're not saving any load_reg() calls as far as I can see ? Indeed you are right. The optimizations are in tcg_gen_deposit_z_i32() vs using tcg_gen_deposit_i32(). I'll reword the description. Thanks, Phil.