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Sat, 11 Sep 2021 07:00:22 -0700 (PDT) Received: from localhost.localdomain ([2a01:4f9:3a:1e26::2]) by smtp.gmail.com with ESMTPSA id u15sm213052lfk.26.2021.09.11.07.00.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 11 Sep 2021 07:00:22 -0700 (PDT) From: Philipp Tomsich To: qemu-devel@nongnu.org Subject: [PATCH v11 03/16] target/riscv: clwz must ignore high bits (use shift-left & changed logic) Date: Sat, 11 Sep 2021 16:00:03 +0200 Message-Id: <20210911140016.834071-4-philipp.tomsich@vrull.eu> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210911140016.834071-1-philipp.tomsich@vrull.eu> References: <20210911140016.834071-1-philipp.tomsich@vrull.eu> MIME-Version: 1.0 Received-SPF: pass client-ip=2a00:1450:4864:20::229; envelope-from=philipp.tomsich@vrull.eu; helo=mail-lj1-x229.google.com X-Spam_score_int: 0 X-Spam_score: 0.0 X-Spam_bar: / X-Spam_report: (0.0 / 5.0 requ) DKIM_SIGNED=0.1, DKIM_VALID=-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: , Cc: Richard Henderson , Kito Cheng , Alistair Francis , Philipp Tomsich Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" Assume clzw being executed on a register that is not sign-extended, such as for the following sequence that uses (1ULL << 63) | 392 as the operand to clzw: bseti a2, zero, 63 addi a2, a2, 392 clzw a3, a2 The correct result of clzw would be 23, but the current implementation returns -32 (as it performs a 64bit clz, which results in 0 leading zero bits, and then subtracts 32). Fix this by changing the implementation to: 1. shift the original register up by 32 2. performs a target-length (64bit) clz 3. return 32 if no bits are set Marking this instruction as 'w-form' (i.e., setting ctx->w) would not correctly model the behaviour, as the instruction should not perform a zero-extensions on the input (after all, it is not a .uw instruction) and the result is always in the range 0..32 (so neither a sign-extension nor a zero-extension on the result will ever be needed). Consequently, we do not set ctx->w and mark the instruction as EXT_NONE. Signed-off-by: Philipp Tomsich Reviewed-by: LIU Zhiwei --- Changes in v11: - Swaps out the EXT_ZERO to EXT_NONE, as no extension is to be performed. Changes in v10: - New patch, fixing correctnes for clzw called on a register with undefined (as in: not properly sign-extended) upper bits. target/riscv/insn_trans/trans_rvb.c.inc | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/target/riscv/insn_trans/trans_rvb.c.inc b/target/riscv/insn_trans/trans_rvb.c.inc index 6c85c89f6d..73d1e45026 100644 --- a/target/riscv/insn_trans/trans_rvb.c.inc +++ b/target/riscv/insn_trans/trans_rvb.c.inc @@ -349,15 +349,17 @@ GEN_TRANS_SHADD(3) static void gen_clzw(TCGv ret, TCGv arg1) { - tcg_gen_clzi_tl(ret, arg1, 64); - tcg_gen_subi_tl(ret, ret, 32); + TCGv t = tcg_temp_new(); + tcg_gen_shli_tl(t, arg1, 32); + tcg_gen_clzi_tl(ret, t, 32); + tcg_temp_free(t); } static bool trans_clzw(DisasContext *ctx, arg_clzw *a) { REQUIRE_64BIT(ctx); REQUIRE_EXT(ctx, RVB); - return gen_unary(ctx, a, EXT_ZERO, gen_clzw); + return gen_unary(ctx, a, EXT_NONE, gen_clzw); } static void gen_ctzw(TCGv ret, TCGv arg1)