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[88.187.86.199]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e33b9eabbsm9408955e9.3.2025.09.24.17.23.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Sep 2025 17:23:17 -0700 (PDT) Message-ID: Date: Thu, 25 Sep 2025 02:23:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] tcg/optimize: Fix folding of vector bitsel Content-Language: en-US To: WANG Rui Cc: Richard Henderson , qemu-devel@nongnu.org, qemu@hev.cc References: <20250919124901.2756538-1-wangrui@loongson.cn> 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::441; envelope-from=philmd@linaro.org; helo=mail-wr1-x441.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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, 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 24/9/25 06:29, WANG Rui wrote: > On Wed, Sep 24, 2025 at 12:03 PM Philippe Mathieu-Daudé > wrote: >> >> On 19/9/25 14:49, WANG Rui wrote: >>> It looks like a typo. >> >> Likely from the TCG_TARGET_HAS_andc_vec case. >> >>> When the false value (C) is the constant -1, the >>> correct fold should be: R = B | ~A >>> >>> Reproducer (LoongArch64 assembly): >>> >>> .text >>> .globl _start >>> _start: >>> vldi $vr1, 3073 >>> vldi $vr2, 1023 >>> vbitsel.v $vr0, $vr2, $vr1, $vr2 >>> vpickve2gr.d $a1, $vr0, 1 >>> xori $a0, $a1, 1 >>> li.w $a7, 93 >>> syscall 0 >>> >>> Fixes: e58b977238e3 ("tcg/optimize: Optimize bitsel_vec") >>> Link: https://github.com/llvm/llvm-project/issues/159610 >>> Signed-off-by: WANG Rui >>> --- >>> tcg/optimize.c | 3 ++- >>> 1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/tcg/optimize.c b/tcg/optimize.c >>> index 3638ab9fea..f69702b26e 100644 >>> --- a/tcg/optimize.c >>> +++ b/tcg/optimize.c >>> @@ -1568,9 +1568,10 @@ static bool fold_bitsel_vec(OptContext *ctx, TCGOp *op) >>> return fold_and(ctx, op); >>> } >>> if (fv == -1 && TCG_TARGET_HAS_orc_vec) { >>> + TCGArg ta = op->args[2]; >>> op->opc = INDEX_op_orc_vec; >>> op->args[2] = op->args[1]; >>> - op->args[1] = op->args[3]; >>> + op->args[1] = ta; >>> return fold_orc(ctx, op); >>> } >>> } >> Looks correct, but I don't understand the swap. Can't we justkeep the >> same argument order for an ORC opcode? I'd have done: >> >> -- >8 -- >> @@ -1569,8 +1569,6 @@ static bool fold_bitsel_vec(OptContext *ctx, TCGOp >> *op) >> } >> if (fv == -1 && TCG_TARGET_HAS_orc_vec) { >> op->opc = INDEX_op_orc_vec; >> - op->args[2] = op->args[1]; >> - op->args[1] = op->args[3]; >> return fold_orc(ctx, op); >> } > > Bitwise logic can be tricky and easy to get wrong. In general, (a | > ~b) != (b | ~a). For example, when a = 0 and b = 1, the results > differ. Oh right. Reviewed-by: Philippe Mathieu-Daudé > >> } >> --- >