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[2001:8b0:1d0::2]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42bb6e355dfsm232251365e9.46.2024.09.05.06.01.07 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Sep 2024 06:01:07 -0700 (PDT) From: Peter Maydell To: qemu-devel@nongnu.org Subject: [PULL 07/25] target/arm: Implement FPCR.EBF=1 semantics for bfdotadd() Date: Thu, 5 Sep 2024 14:00:42 +0100 Message-Id: <20240905130100.298768-8-peter.maydell@linaro.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240905130100.298768-1-peter.maydell@linaro.org> References: <20240905130100.298768-1-peter.maydell@linaro.org> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::32c; envelope-from=peter.maydell@linaro.org; helo=mail-wm1-x32c.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, 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-bounces+qemu-devel=archiver.kernel.org@nongnu.org Implement the FPCR.EBF=1 semantics for bfdotadd() operations: * is_ebf() sets up fpst and fpst_odd * bfdotadd_ebf() implements the fused paired-multiply-and-add operation that we need The paired-multiply-and-add is similar to f16_dotadd() and we use the same trick here as in that function, but the inputs here are bfloat16 rather than float16. Signed-off-by: Peter Maydell Reviewed-by: Richard Henderson --- target/arm/tcg/vec_helper.c | 57 +++++++++++++++++++++++++++++++++++-- 1 file changed, 54 insertions(+), 3 deletions(-) diff --git a/target/arm/tcg/vec_helper.c b/target/arm/tcg/vec_helper.c index b0de74b55f1..22ddb968817 100644 --- a/target/arm/tcg/vec_helper.c +++ b/target/arm/tcg/vec_helper.c @@ -2792,7 +2792,20 @@ DO_MMLA_B(gvec_usmmla_b, do_usmmla_b) bool is_ebf(CPUARMState *env, float_status *statusp, float_status *oddstatusp) { - /* FPCR is ignored for BFDOT and BFMMLA. */ + /* + * For BFDOT, BFMMLA, etc, the behaviour depends on FPCR.EBF. + * For EBF = 0, we ignore the FPCR bits which determine rounding + * mode and denormal-flushing, and we do unfused multiplies and + * additions with intermediate rounding of all products and sums. + * For EBF = 1, we honour FPCR rounding mode and denormal-flushing bits, + * and we perform a fused two-way sum-of-products without intermediate + * rounding of the products. + * In either case, we don't set fp exception flags. + * + * EBF is AArch64 only, so even if it's set in the FPCR it has + * no effect on AArch32 instructions. + */ + bool ebf = is_a64(env) && env->vfp.fpcr & FPCR_EBF; *statusp = (float_status){ .tininess_before_rounding = float_tininess_before_rounding, .float_rounding_mode = float_round_to_odd_inf, @@ -2801,7 +2814,18 @@ bool is_ebf(CPUARMState *env, float_status *statusp, float_status *oddstatusp) .default_nan_mode = true, }; - return false; + if (ebf) { + float_status *fpst = &env->vfp.fp_status; + set_flush_to_zero(get_flush_to_zero(fpst), statusp); + set_flush_inputs_to_zero(get_flush_inputs_to_zero(fpst), statusp); + set_float_rounding_mode(get_float_rounding_mode(fpst), statusp); + + /* EBF=1 needs to do a step with round-to-odd semantics */ + *oddstatusp = *statusp; + set_float_rounding_mode(float_round_to_odd, oddstatusp); + } + + return ebf; } float32 bfdotadd(float32 sum, uint32_t e1, uint32_t e2, float_status *fpst) @@ -2823,7 +2847,34 @@ float32 bfdotadd(float32 sum, uint32_t e1, uint32_t e2, float_status *fpst) float32 bfdotadd_ebf(float32 sum, uint32_t e1, uint32_t e2, float_status *fpst, float_status *fpst_odd) { - g_assert_not_reached(); + /* + * Compare f16_dotadd() in sme_helper.c, but here we have + * bfloat16 inputs. In particular that means that we do not + * want the FPCR.FZ16 flush semantics, so we use the normal + * float_status for the input handling here. + */ + float64 e1r = float32_to_float64(e1 << 16, fpst); + float64 e1c = float32_to_float64(e1 & 0xffff0000u, fpst); + float64 e2r = float32_to_float64(e2 << 16, fpst); + float64 e2c = float32_to_float64(e2 & 0xffff0000u, fpst); + float64 t64; + float32 t32; + + /* + * The ARM pseudocode function FPDot performs both multiplies + * and the add with a single rounding operation. Emulate this + * by performing the first multiply in round-to-odd, then doing + * the second multiply as fused multiply-add, and rounding to + * float32 all in one step. + */ + t64 = float64_mul(e1r, e2r, fpst_odd); + t64 = float64r32_muladd(e1c, e2c, t64, 0, fpst); + + /* This conversion is exact, because we've already rounded. */ + t32 = float64_to_float32(t64, fpst); + + /* The final accumulation step is not fused. */ + return float32_add(sum, t32, fpst); } void HELPER(gvec_bfdot)(void *vd, void *vn, void *vm, void *va,