From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 2153) id 934F4385840C; Sat, 19 Mar 2022 12:53:50 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 934F4385840C MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="utf-8" From: Jakub Jelinek To: gcc-cvs@gcc.gnu.org Subject: [gcc r12-7721] i386: Don't emit pushf; pop for __builtin_ia32_readeflags_u* with unused lhs [PR104971] X-Act-Checkin: gcc X-Git-Author: Jakub Jelinek X-Git-Refname: refs/heads/master X-Git-Oldrev: 2663d18356b0a62f5a800c7e5596d814cd3c2c41 X-Git-Newrev: b60bc913cca7439d29a7ec9e9a7f448d8841b43c Message-Id: <20220319125350.934F4385840C@sourceware.org> Date: Sat, 19 Mar 2022 12:53:50 +0000 (GMT) X-BeenThere: gcc-cvs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-cvs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 19 Mar 2022 12:53:50 -0000 https://gcc.gnu.org/g:b60bc913cca7439d29a7ec9e9a7f448d8841b43c commit r12-7721-gb60bc913cca7439d29a7ec9e9a7f448d8841b43c Author: Jakub Jelinek Date: Sat Mar 19 13:53:12 2022 +0100 i386: Don't emit pushf;pop for __builtin_ia32_readeflags_u* with unused lhs [PR104971] __builtin_ia32_readeflags_u* aren't marked const or pure I think intentionally, so that they aren't CSEd from different regions of a function etc. because we don't and can't easily track all dependencies between it and surrounding code (if somebody looks at the condition flags, it is dependent on the vast majority of instructions). But the builtin itself doesn't have any side-effects, so if we ignore the result of the builtin, there is no point to emit anything. There is a LRA bug that miscompiles the testcase which this patch makes latent, which is certainly worth fixing too, but IMHO this change (and maybe ix86_gimple_fold_builtin too which would fold it even earlier when it looses lhs) is worth it as well. 2022-03-19 Jakub Jelinek PR middle-end/104971 * config/i386/i386-expand.cc (ix86_expand_builtin) : If ignore, don't push/pop anything and just return const0_rtx. * gcc.target/i386/pr104971.c: New test. Diff: --- gcc/config/i386/i386-expand.cc | 3 +++ gcc/testsuite/gcc.target/i386/pr104971.c | 18 ++++++++++++++++++ 2 files changed, 21 insertions(+) diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc index e85641d3204..22728545b83 100644 --- a/gcc/config/i386/i386-expand.cc +++ b/gcc/config/i386/i386-expand.cc @@ -13556,6 +13556,9 @@ rdseed_step: return target; case IX86_BUILTIN_READ_FLAGS: + if (ignore) + return const0_rtx; + emit_insn (gen_push (gen_rtx_REG (word_mode, FLAGS_REG))); if (optimize diff --git a/gcc/testsuite/gcc.target/i386/pr104971.c b/gcc/testsuite/gcc.target/i386/pr104971.c new file mode 100644 index 00000000000..80ac6b613f1 --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/pr104971.c @@ -0,0 +1,18 @@ +/* PR middle-end/104971 */ +/* { dg-do run } */ +/* { dg-options "-O2" } */ + +#include + +__attribute__((noipa)) void +foo (void) +{ + __readeflags (); +} + +int +main () +{ + foo (); + return 0; +}