From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by sourceware.org (Postfix) with ESMTPS id 40319385803C for ; Mon, 23 Aug 2021 13:55:40 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 40319385803C Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id DBFDC21F82; Mon, 23 Aug 2021 13:55:38 +0000 (UTC) Received: from murzim.suse.de (murzim.suse.de [10.160.4.192]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id D2614A3BB0; Mon, 23 Aug 2021 13:55:38 +0000 (UTC) Date: Mon, 23 Aug 2021 15:55:38 +0200 (CEST) From: Richard Biener To: Qing Zhao cc: Jakub Jelinek , Nick Alcock via Gcc-patches , Kees Cook Subject: Re: [patch][version 6] add -ftrivial-auto-var-init and variable attribute "uninitialized" to gcc In-Reply-To: <2F266F68-454F-4E0E-B38B-293F60DE2B1C@oracle.com> Message-ID: References: <52E29277-1403-4755-901A-528116C43FB8@oracle.com> <517EA40B-9500-4090-8F03-B4A9CECC62F8@oracle.com> <8B2F93E8-C3AC-49D2-B764-D4DD8A150A52@oracle.com> <786F370D-4A45-4F66-846C-A3437A162A65@oracle.com> <986D883E-A346-456A-B335-4185D4B136B5@oracle.com> <7AD092FB-62D6-4C87-B141-FD649E7B3F93@oracle.com> <2F266F68-454F-4E0E-B38B-293F60DE2B1C@oracle.com> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 X-Spam-Status: No, score=-4.8 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 23 Aug 2021 13:55:50 -0000 On Thu, 19 Aug 2021, Qing Zhao wrote: > > > > On Aug 19, 2021, at 4:00 AM, Richard Biener wrote: > > > > On Wed, 18 Aug 2021, Qing Zhao wrote: > > > >> > >> > >>> On Aug 18, 2021, at 2:15 AM, Richard Biener wrote: > >>> > >>> On Tue, 17 Aug 2021, Qing Zhao wrote: > >>> > >>>> > >>>> > >>>>> On Aug 17, 2021, at 9:50 AM, Qing Zhao via Gcc-patches wrote: > >>>>> > >>>>> > >>>>> > >>>>>> On Aug 17, 2021, at 3:29 AM, Richard Biener wrote: > >>>>>> > >>>>>> On Mon, 16 Aug 2021, Qing Zhao wrote: > >>>>>> > >>>>>>> My current code for expand_DEFERRED_INIT is like the following, could you check and see whether there is any issue for it: > >>>>>>> > >>>>>>> #define INIT_PATTERN_VALUE 0xFE > >>>>>>> static void > >>>>>>> expand_DEFERRED_INIT (internal_fn, gcall *stmt) > >>>>>>> { > >>>>>>> tree lhs = gimple_call_lhs (stmt); > >>>>>>> tree var_size = gimple_call_arg (stmt, 0); > >>>>>>> enum auto_init_type init_type > >>>>>>> = (enum auto_init_type) TREE_INT_CST_LOW (gimple_call_arg (stmt, 1)); > >>>>>>> bool is_vla = (bool) TREE_INT_CST_LOW (gimple_call_arg (stmt, 2)); > >>>>>>> > >>>>>>> tree var_type = TREE_TYPE (lhs); > >>>>>>> gcc_assert (init_type > AUTO_INIT_UNINITIALIZED); > >>>>>>> > >>>>>>> if (is_vla || (!use_register_for_decl (lhs))) > >>>>>>> { > >>>>>>> if (TREE_CODE (lhs) == SSA_NAME) > >>>>>>> lhs = SSA_NAME_VAR (lhs); > >>>>>> > >>>>>> this should not be necessary (in fact you shouldn't see a SSA_NAME > >>>>>> here, if you do then using SSA_NAME_VAR is wrong) > >>>>> You mean during RTL expansion phase, all SSA_NAMEs are gone already? > >>>> > >>>> Actually, the lhs could be SSA_NAME here, > >>>> > >>>> Breakpoint 1, expand_DEFERRED_INIT (stmt=0x7fffe96ae348) at ../../latest-gcc/gcc/internal-fn.c:3021 > >>>> 3021 mark_addressable (lhs); > >>>> (gdb) call debug_tree(lhs) > >>>> >>>> type >>>> size > >>>> unit-size > >>>> align:32 warn_if_not_align:0 symtab:0 alias-set 2 canonical-type 0x7fffe959b2a0 precision:32 > >>>> pointer_to_this > > >>>> visited var > >>>> def_stmt temp1_5 = .DEFERRED_INIT (4, 2, 0, &"temp1"[0]); > >>>> version:5> > >>>> > >>>> when I deleted: > >>>> > >>>> if (TREE_CODE (lhs) == SSA_NAME > >>>> lhs = SSA_NAME_VAR (lhs); > >>> > >>> but then using SSA_NAME_VAR is broken. I suspect use_register_for_decl > >>> isn't the correct thing to look at. I think we need to look at what > >>> the LHS expanded to if it is a SSA_VAR_P (that includes SSA names > >>> but also plain DECLs but not what we get from VLAs where we'd see > >>> *ptr). So sth like > >>> > >>> bool reg_lhs; > >>> if (SSA_VAR_P (lhs)) > >>> { > >>> rtx tem = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE); > >>> reg_lhs = !MEM_P (tem); > >>> /* If not MEM_P reg_lhs should be REG_P or SUBREG_P (but maybe > >>> also CONCAT or lowpart...?) */ > >>> } > >>> else > >>> { > >>> gcc_assert (is_vla); > >>> reg_lhs = false; > >>> } > >>> > >>> if (!reg_lhs) > >>> memset path > >>> else > >>> expand_assignment path > >> > >> After making the following change: > >> > >> + bool reg_lhs = true; > >> > >> tree var_type = TREE_TYPE (lhs); > >> gcc_assert (init_type > AUTO_INIT_UNINITIALIZED); > >> > >> - if (is_vla || (!use_register_for_decl (lhs))) > >> + if (SSA_VAR_P (lhs)) > >> + { > >> + rtx tem = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE); > >> + reg_lhs = !MEM_P (tem); > >> + } > >> + else > >> + { > >> + gcc_assert (is_vla); > >> + reg_lhs = false; > >> + } > >> + > >> + if (!reg_lhs) > >> { > >> > >> I got exactly the same internal error that failed at expr.c: > >> > >> 8436 /* We must have made progress. */ > >> 8437 gcc_assert (inner != exp); > >> > >> > >> Looks like for the following code: > >> > >> 3026 if (!reg_lhs) > >> 3027 { > >> 3028 /* If this is a VLA or the variable is not in register, > >> 3029 expand to a memset to initialize it. */ > >> 3030 mark_addressable (lhs); > >> 3031 tree var_addr = build_fold_addr_expr (lhs); > >> 3032 > >> 3033 tree value = (init_type == AUTO_INIT_PATTERN) ? > >> 3034 build_int_cst (integer_type_node, > >> 3035 INIT_PATTERN_VALUE) : > >> 3036 integer_zero_node; > >> 3037 tree m_call = build_call_expr (builtin_decl_implicit (BUILT_IN_MEMSET), > >> 3038 3, var_addr, value, var_size); > >> 3039 /* Expand this memset call. */ > >> 3040 expand_builtin_memset (m_call, NULL_RTX, TYPE_MODE (var_type)); > >> 3041 } > >> > >> At line 3030, “lhs” could be a SSA_NAME. > >> > >> My questions are: > >> > >> 1. Could the routine “mark_addressable” and “build_fold_addr_expr” be applied on SSA_NAME? > > > > No. > > > >> 2. Could the routine “expand_builtin_memset” be applied on the memset call whose “DEST” is > >> an address expression on SSA_NAME? > > > > No. > > > >> 3. Within “expand_DEFERRED_INIT”, can I call “expand_builtin_memset” to expand .DEFERRED_INIT? > > > > Well, not with "invalid" GENERIC I fear (address of a SSA name). > > > >> I suspect that one of the above 3 might be the issue, but not sure which one? > > > > All of the above ;) So while reg_lhs is now precise as to how the > > variable will end up (the SSA name will end up as a stack variable in this > > case, for whatever reason), expansion via memcpy only works when > > working on the RTL representation. The usual "workaround" (ugh) > > is to use make_tree (), so in the !reg_lhs path you'd do > > > > /* Get a new GENERIC representation for the RTL. That's necesary > > in case LHS is an SSA name. */ > > lhs = make_tree (TREE_TYPE (lhs), tem); > > This resolved the issue. > > Another question, > > Previously, I used > > if (TREE_CODE (lhs) == SSA_NAME) > lhs = SSA_NAME_VAR (lhs); > > To resolve this issue. The purpose looks like the same as “make_tree”, just get an generic tree for the LHS. > > Why you said using SSA_NAME_VAR is broken? Is it because SSA_NAME_VAR will not always return a valid TREE? Because it's simply the wrong entity - I have no idea why that even worked. Ah, cfgexpand associates it with some DECL_RTL for the benefit of debug info. But it's still wrong. > I should use as following > > > If (TREE_CODE (lhs) == SSA_NAME) && SSA_NAME_VAR (lhs)) > Lhs = SSA_NAME_VAR (lhs) > > ? No. A SSA_NAME_VAR can have multiple SSA_NAMEs (obviously) and they do not necessarily have to be allocated to the same variable partition - that is, there's no 1:1 relationship between SSA_NAME and stack slot or (pseudo) register. You want to initialize the storage associated with the SSA_NAME in the .DEFERRED_INIT call, not some other storage. > > > > alternatively you could maybe do > > > > if (DECL_P (lhs)) > > { > > + rtx tem = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE); > > + reg_lhs = !MEM_P (tem); > > } > > else if (TREE_CODE (lhs) == SSA_NAME) > > reg_lhs = true; > > else > > reg_lhs = false; > > > > thus treat SSA names as register storage always (even if it will end > > up on the stack). > > My question here, for a complicate structure SSA_NAME, will expanding through memset better than expand_asssignment? It depends. In the end I'd consider it a missed-optimization bug on the side that generates worse code - but I do expect cases will exist for both. Clearly memset will be worse when dealing with register initialization (thus the !MEM_P check) and I expect memset to be OK for stack where member-wise init esp. with non-zero might turn up worse code. Richard. > Qing > > > > Richard. > > > >> Thanks a lot. > >> > >> Qing > >> > >> > >> > >>> bool reg_lhs; > >>> if (SSA_VAR_P (lhs)) > >>> { > >>> rtx tem = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE); > >>> reg_lhs = !MEM_P (tem); > >>> /* If not MEM_P reg_lhs should be REG_P or SUBREG_P (but maybe > >>> also CONCAT or lowpart...?) */ > >>> } > >>> else > >>> { > >>> gcc_assert (is_vla); > >>> reg_lhs = false; > >>> } > >> > >> > >>> > >>>> Many testing cases failed with internal compiler error: > >>>> > >>>> /home/opc/Work/GCC/latest-gcc/gcc/testsuite/c-c++-common/auto-init-3.c:9:9: internal compiler error: in expand_expr_addr_expr_1, at expr.c:8437 > >>>> 0xe237aa expand_expr_addr_expr_1 > >>>> ../../latest-gcc/gcc/expr.c:8437 > >>>> 0xe24059 expand_expr_addr_expr > >>>> ../../latest-gcc/gcc/expr.c:8525 > >>>> 0xe32b56 expand_expr_real_1(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool) > >>>> ../../latest-gcc/gcc/expr.c:11741 > >>>> 0xe2da52 expand_expr_real_1(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool) > >>>> ../../latest-gcc/gcc/expr.c:10777 > >>>> 0xe24706 expand_expr_real(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool) > >>>> ../../latest-gcc/gcc/expr.c:8713 > >>>> 0xc13f15 expand_expr > >>>> ../../latest-gcc/gcc/expr.h:301 > >>>> 0xc17acb get_memory_rtx > >>>> ../../latest-gcc/gcc/builtins.c:1370 > >>>> 0xc2223d expand_builtin_memset_args > >>>> ../../latest-gcc/gcc/builtins.c:4102 > >>>> 0xc21a20 expand_builtin_memset(tree_node*, rtx_def*, machine_mode) > >>>> ../../latest-gcc/gcc/builtins.c:3886 > >>>> 0xfb5c85 expand_DEFERRED_INIT > >>>> ../../latest-gcc/gcc/internal-fn.c:3031 > >>>> > >>>> > >>>> So, did I do anything wrong? > >>>> > >>>> Qing > >>> > >>> -- > >>> Richard Biener > >>> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg, > >>> Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg) > >> > >> > > > > -- > > Richard Biener > > SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg, > > Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg) > > -- Richard Biener SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)