From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52840) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gHWpq-0003LN-Jc for qemu-devel@nongnu.org; Tue, 30 Oct 2018 12:25:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gHWpn-0005qo-3X for qemu-devel@nongnu.org; Tue, 30 Oct 2018 12:25:40 -0400 From: Peter Maydell Date: Tue, 30 Oct 2018 16:25:17 +0000 Message-Id: <20181030162517.21816-1-peter.maydell@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Subject: [Qemu-devel] [PATCH for-3.1] target/arm: Remove can't-happen if() from handle_vec_simd_shli() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-arm@nongnu.org, qemu-devel@nongnu.org Cc: patches@linaro.org, =?UTF-8?q?Alex=20Benn=C3=A9e?= , Richard Henderson In handle_vec_simd_shli() we have a check: if (size > 3 && !is_q) { unallocated_encoding(s); return; } However this can never be true, because we calculate int size = 32 - clz32(immh) - 1; where immh is a 4 bit field which we know cannot be all-zeroes. So the clz32() return must be in {28,29,30,31} and the resulting size is in {0,1,2,3}, and "size > 3" is never true. This unnecessary code confuses Coverity's analysis: in CID 1396476 it thinks we might later index off the end of an array because the condition implies that we might have a size > 3. Remove the code, and instead assert that the size is in [0..3], since the decode that enforces that is somewhat distant from this function. Signed-off-by: Peter Maydell --- Alex, if you could run this through the risu testset just as a sanity check that would be very helpful. target/arm/translate-a64.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c index 88195ab9490..fd36425f1ae 100644 --- a/target/arm/translate-a64.c +++ b/target/arm/translate-a64.c @@ -9483,12 +9483,10 @@ static void handle_vec_simd_shli(DisasContext *s, bool is_q, bool insert, int immhb = immh << 3 | immb; int shift = immhb - (8 << size); - if (extract32(immh, 3, 1) && !is_q) { - unallocated_encoding(s); - return; - } + /* Range of size is limited by decode: immh is a non-zero 4 bit field */ + assert(size >= 0 && size <= 3); - if (size > 3 && !is_q) { + if (extract32(immh, 3, 1) && !is_q) { unallocated_encoding(s); return; } -- 2.19.1