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[174.21.72.39]) by smtp.gmail.com with ESMTPSA id o6sm13337072pjk.4.2021.08.29.23.28.23 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 29 Aug 2021 23:28:23 -0700 (PDT) From: Richard Henderson To: qemu-devel@nongnu.org Subject: [PATCH 48/48] tcg/optimize: Propagate sign info for shifting Date: Sun, 29 Aug 2021 23:24:51 -0700 Message-Id: <20210830062451.639572-49-richard.henderson@linaro.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210830062451.639572-1-richard.henderson@linaro.org> References: <20210830062451.639572-1-richard.henderson@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::1036; envelope-from=richard.henderson@linaro.org; helo=mail-pj1-x1036.google.com X-Spam_score_int: -1 X-Spam_score: -0.2 X-Spam_bar: / X-Spam_report: (-0.2 / 5.0 requ) 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: 2.1.23 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" For constant shifts, we can simply shift the s_mask. For variable shifts, we know that sar does not reduce the s_mask, which helps for sequences like ext32s_i64 t, in sar_i64 t, t, v ext32s_i64 out, t allowing the final extend to be eliminated. Signed-off-by: Richard Henderson --- tcg/optimize.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++--- 1 file changed, 47 insertions(+), 3 deletions(-) diff --git a/tcg/optimize.c b/tcg/optimize.c index dad72b2ff5..db3661c975 100644 --- a/tcg/optimize.c +++ b/tcg/optimize.c @@ -84,6 +84,18 @@ static uint64_t smask_from_zmask(uint64_t zmask) return ~(~0ull >> rep); } +/* + * Recreate a properly left-aligned smask after manipulation. + * Some bit-shuffling, particularly shifts and rotates, may + * retain sign bits on the left, but may scatter disconnected + * sign bits on the right. Retain only what remains to the left. + */ +static uint64_t smask_from_smask(int64_t smask) +{ + /* Only the 1 bits are significant for smask */ + return smask_from_zmask(~smask); +} + static inline TempOptInfo *ts_info(TCGTemp *ts) { return ts->state_ptr; @@ -1795,18 +1807,50 @@ static bool fold_sextract(OptContext *ctx, TCGOp *op) static bool fold_shift(OptContext *ctx, TCGOp *op) { + uint64_t s_mask, z_mask, sign; + if (fold_const2(ctx, op) || fold_ix_to_i(ctx, op, 0) || fold_xi_to_x(ctx, op, 0)) { return true; } + s_mask = arg_info(op->args[1])->s_mask; + z_mask = arg_info(op->args[1])->z_mask; + if (arg_is_const(op->args[2])) { - ctx->z_mask = do_constant_folding(op->opc, ctx->type, - arg_info(op->args[1])->z_mask, - arg_info(op->args[2])->val); + int sh = arg_info(op->args[2])->val; + + ctx->z_mask = do_constant_folding(op->opc, ctx->type, z_mask, sh); + + s_mask = do_constant_folding(op->opc, ctx->type, s_mask, sh); + ctx->s_mask = smask_from_smask(s_mask); + return fold_masks(ctx, op); } + + switch (op->opc) { + CASE_OP_32_64(sar): + /* + * Arithmetic right shift will not reduce the number of + * input sign repetitions. + */ + ctx->s_mask = s_mask; + break; + CASE_OP_32_64(shr): + /* + * If the sign bit is known zero, then logical right shift + * will not reduced the number of input sign repetitions. + */ + sign = (s_mask & -s_mask) >> 1; + if (!(z_mask & sign)) { + ctx->s_mask = s_mask; + } + break; + default: + break; + } + return false; } -- 2.25.1