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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH] Hexagon (target/hexagon) implement mutability mask for GPRs Content-Language: en-US To: Brian Cain , qemu-devel@nongnu.org, tsimpson@quicinc.com References: <20220901212931.27310-1-bcain@quicinc.com> From: Richard Henderson In-Reply-To: <20220901212931.27310-1-bcain@quicinc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2a00:1450:4864:20::330; envelope-from=richard.henderson@linaro.org; helo=mail-wm1-x330.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, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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" On 9/1/22 22:29, Brian Cain wrote: > +void gen_masked_reg_write(TCGv cur_val, TCGv in_val, TCGv out_val, > + target_ulong reg_mask) { > + TCGv set_bits = tcg_temp_new(); > + TCGv cleared_bits = tcg_temp_new(); > + > + /* > + * set_bits = in_val & reg_mask > + * cleared_bits = (~in_val) & reg_mask > + */ > + tcg_gen_andi_tl(set_bits, in_val, reg_mask); > + tcg_gen_not_tl(cleared_bits, in_val); > + tcg_gen_andi_tl(cleared_bits, cleared_bits, reg_mask); > + > + /* > + * result = (reg_cur | set_bits) & (~cleared_bits) > + */ > + tcg_gen_not_tl(cleared_bits, cleared_bits); > + tcg_gen_or_tl(set_bits, set_bits, cur_val); > + tcg_gen_and_tl(out_val, set_bits, cleared_bits); This is overly complicated. It should be out = (in & mask) | (cur & ~mask) which is only 3 operations instead of 6: tcg_gen_andi_tl(t1, in_val, reg_mask); tcg_gen_andi_tl(t2, cur_val, ~reg_mask); tcg_gen_or_tl(out_val, t1, t2); I'm surprised about new files for this simple operation. Surely a subroutine within genptr.c would be sufficient. > +static const hexagon_mut_entry gpr_mut_masks[HEX_REG_LAST_VALUE] = { > + [HEX_REG_PC] = {true, 0x00000000}, > + [HEX_REG_GP] = {true, 0xffffffc0}, > + [HEX_REG_USR] = {true, 0x3ecfff3f}, > + [HEX_REG_UTIMERLO] = {true, 0x00000000}, > + [HEX_REG_UTIMERHI] = {true, 0x00000000}, > +}; ... > static inline void gen_log_reg_write(int rnum, TCGv val) > { > - tcg_gen_mov_tl(hex_new_value[rnum], val); > + const hexagon_mut_entry entry = gpr_mut_masks[rnum]; > + if (entry.present) { > + gen_masked_reg_write(hex_gpr[rnum], val, hex_new_value[rnum], > + entry.mask); > + } else { > + tcg_gen_mov_tl(hex_new_value[rnum], val); > + } You could avoid the structure and .present flag by initializing all other entries to UINT32_MAX. E.g. static const target_ulong gpr_mut_masks[HEX_REG_LAST_VALUE] = { [0 ... HEX_REG_LAST_VALUE - 1] = UINT32_MAX, [HEX_REG_PC] = 0 ... }; It might be clearer, and easier to initialize, if you invert the sense of the mask: only set bits that are immutable, so that you get static const target_ulong gpr_immutable_masks[HEX_REG_LAST_VALUE] = { [HEX_REG_PC] = UINT32_MAX, [HEX_REG_GP] = 0x3f, ... }; r~