From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-x52d.google.com (mail-ed1-x52d.google.com [IPv6:2a00:1450:4864:20::52d]) by sourceware.org (Postfix) with ESMTPS id 129F93858D35 for ; Mon, 22 Nov 2021 11:40:07 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 129F93858D35 Received: by mail-ed1-x52d.google.com with SMTP id r11so75403780edd.9 for ; Mon, 22 Nov 2021 03:40:07 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=yswDShrvoNmzRP+ht1CJtRlSeOT/Ki3TbQwYKGNmV+0=; b=rmUCGWAiwI5/X4bNg+ousCp5aKH/IdD6idco3aiYNYXsloUcMtXqePJYgUpVKsouIU YvRaWYWLEpVoPU2wmkDGfMD0LifFQkcdDUrkvEAcQVSqtBacQNHALEV7zx/E9pBDNmX/ ytbYMfy6Cu8uLqMXWo3NtMHm3a1kuVXzeEf6wb92TJRgou3R4kKgQVzazkZFlVVe1n/L urNUeqCb2rWnHgu2ZVCK2NTVixhnuzwBcxY79BsBdhFcluBGVlySSW5FRt5Jorw6yRCJ Rs3qDew2UehlIvJXuoqDLWjX9VpMGeMYWs93cUHSDt5aUBaiwty9EDCZ527djyDyMcal w+YQ== X-Gm-Message-State: AOAM531cF0onF60IuaxGhHhCCQBgG65Pz4ylr2xBJzEH66Aq4fQdVjxp nvaCxTx1btWd0metuyNygkvIslxOtwUt/1nNQ/g= X-Google-Smtp-Source: ABdhPJxa0Q7BZFNEy8AdSHyqzzrxlaU6bwVbdbfJwkfr1Wz6CJyxuIgcZLkKqsyk+iqy2rGwGSvINimKJe7RA0LiS5g= X-Received: by 2002:a17:906:974b:: with SMTP id o11mr22402230ejy.204.1637581205933; Mon, 22 Nov 2021 03:40:05 -0800 (PST) MIME-Version: 1.0 References: <1635328798-30341-1-git-send-email-apinski@marvell.com> In-Reply-To: From: Richard Biener Date: Mon, 22 Nov 2021 12:39:55 +0100 Message-ID: Subject: Re: [V2/PATCH] Fix tree-optimization/102216: missed optimization causing Warray-bounds To: Andrew Pinski Cc: Andrew Pinski , GCC Patches Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-8.5 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, 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 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, 22 Nov 2021 11:40:09 -0000 On Mon, Nov 22, 2021 at 9:40 AM Andrew Pinski wrote: > > On Wed, Oct 27, 2021 at 3:42 AM Richard Biener via Gcc-patches > wrote: > > > > On Wed, Oct 27, 2021 at 12:00 PM apinski--- via Gcc-patches > > wrote: > > > > > > From: Andrew Pinski > > > > > > The problem here is tree-ssa-forwprop.c likes to produce > > > &MEM [(void *)_4 + 152B] which is the same as > > > _4 p+ 152 which the rest of GCC likes better. > > > This implements this transformation back to pointer plus to > > > improve better code generation later on. > > > > Why do you think so? Can you pin-point the transform that now > > fixes the new testcase? > > So we had originally: > language_names_p_9 = &MEM [(void *)_4 + 24B]; > ... > _2 = _4 + 40; Of course if that would have been _2 = &MEM [_4 + 40B]; the issue would be fixed as well. That said, I agree that _4 + 40 is better but I think we should canonicalize all &MEM[SSA + CST] this way. There is a canonicalization phase in fold_stmt_1: /* First do required canonicalization of [TARGET_]MEM_REF addresses after propagation. ??? This shouldn't be done in generic folding but in the propagation helpers which also know whether an address was propagated. Also canonicalize operand order. */ switch (gimple_code (stmt)) { case GIMPLE_ASSIGN: if (gimple_assign_rhs_class (stmt) == GIMPLE_SINGLE_RHS) { tree *rhs = gimple_assign_rhs1_ptr (stmt); if ((REFERENCE_CLASS_P (*rhs) || TREE_CODE (*rhs) == ADDR_EXPR) && maybe_canonicalize_mem_ref_addr (rhs)) changed = true; where this could be done (apart from adding a match.pd pattern for this). > if (_2 != language_names_p_9) > > Forwprop is able to figure out that the above if statement is now > always false as we have (_4 +p 40) != (_4 +p 24) which gets simplified > via a match-and-simplify pattern (). > Does that answer your question? > > I will look into the other comments in a new patch. > > Thanks, > Andrew > > > > > Comments below > > > > > OK? Bootstrapped and tested on aarch64-linux-gnu. > > > > > > Changes from v1: > > > * v2: Add comments. > > > > > > gcc/ChangeLog: > > > > > > PR tree-optimization/102216 > > > * tree-ssa-forwprop.c (rewrite_assign_addr): New function. > > > (forward_propagate_addr_expr_1): Use rewrite_assign_addr > > > when rewriting into the addr_expr into an assignment. > > > > > > gcc/testsuite/ChangeLog: > > > > > > PR tree-optimization/102216 > > > * g++.dg/tree-ssa/pr102216.C: New test. > > > --- > > > gcc/testsuite/g++.dg/tree-ssa/pr102216.C | 22 +++++++++ > > > gcc/tree-ssa-forwprop.c | 58 ++++++++++++++++++------ > > > 2 files changed, 67 insertions(+), 13 deletions(-) > > > create mode 100644 gcc/testsuite/g++.dg/tree-ssa/pr102216.C > > > > > > diff --git a/gcc/testsuite/g++.dg/tree-ssa/pr102216.C b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C > > > new file mode 100644 > > > index 00000000000..b903e4eb57d > > > --- /dev/null > > > +++ b/gcc/testsuite/g++.dg/tree-ssa/pr102216.C > > > @@ -0,0 +1,22 @@ > > > +/* { dg-options "-O2 -fdump-tree-optimized" } */ > > > +void link_error (); > > > +void g () > > > +{ > > > + const char **language_names; > > > + > > > + language_names = new const char *[6]; > > > + > > > + const char **language_names_p = language_names; > > > + > > > + language_names_p++; > > > + language_names_p++; > > > + language_names_p++; > > > + > > > + if ( (language_names_p) - (language_names+3) != 0) > > > + link_error(); > > > + delete[] language_names; > > > +} > > > +/* We should have removed the link_error on the gimple level as GCC should > > > + be able to tell that language_names_p is the same as language_names+3. */ > > > +/* { dg-final { scan-tree-dump-times "link_error" 0 "optimized" } } */ > > > + > > > diff --git a/gcc/tree-ssa-forwprop.c b/gcc/tree-ssa-forwprop.c > > > index a830bab78ba..e4331c60525 100644 > > > --- a/gcc/tree-ssa-forwprop.c > > > +++ b/gcc/tree-ssa-forwprop.c > > > @@ -637,6 +637,47 @@ forward_propagate_into_cond (gimple_stmt_iterator *gsi_p) > > > return 0; > > > } > > > > > > +/* Rewrite the DEF_RHS as needed into the (plain) use statement. */ > > > + > > > +static void > > > +rewrite_assign_addr (gimple_stmt_iterator *use_stmt_gsi, tree def_rhs) > > > +{ > > > + tree def_rhs_base; > > > + poly_int64 def_rhs_offset; > > > + > > > + /* Get the base and offset. */ > > > + if ((def_rhs_base = get_addr_base_and_unit_offset (TREE_OPERAND (def_rhs, 0), > > > + &def_rhs_offset))) > > > > So this will cause us to rewrite &MEM[p_1].a.b.c; to a pointer-plus, > > right? Don't > > we want to preserve that for object-size stuff? So maybe directly pattern > > match ADDR_EXPR > only? > > > > > + { > > > + tree new_ptr; > > > + poly_offset_int off = 0; > > > + > > > + /* If the base was a MEM, then add the offset to the other > > > + offset and adjust the base. */ > > > + if (TREE_CODE (def_rhs_base) == MEM_REF) > > > + { > > > + off += mem_ref_offset (def_rhs_base); > > > + new_ptr = TREE_OPERAND (def_rhs_base, 0); > > > + } > > > + else > > > + new_ptr = build_fold_addr_expr (def_rhs_base); > > > + > > > + /* If we have the new base is not an address express, then use a p+ expression > > > + as the new expression instead of &MEM[x, offset]. */ > > > + if (TREE_CODE (new_ptr) != ADDR_EXPR) > > > + { > > > + tree offset = wide_int_to_tree (sizetype, off); > > > + def_rhs = build2 (POINTER_PLUS_EXPR, TREE_TYPE (def_rhs), new_ptr, offset); > > > > Ick. You should be able to use gimple_assign_set_rhs_with_ops. > > > > > + } > > > + } > > > + > > > + /* Replace the rhs with the new expression. */ > > > + def_rhs = unshare_expr (def_rhs); > > > > and definitely no need to unshare anything here? > > > > > + gimple_assign_set_rhs_from_tree (use_stmt_gsi, def_rhs); > > > + gimple *use_stmt = gsi_stmt (*use_stmt_gsi); > > > + update_stmt (use_stmt); > > > +} > > > + > > > /* We've just substituted an ADDR_EXPR into stmt. Update all the > > > relevant data structures to match. */ > > > > > > @@ -696,8 +737,8 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs, > > > if (single_use_p > > > && useless_type_conversion_p (TREE_TYPE (lhs), TREE_TYPE (def_rhs))) > > > { > > > - gimple_assign_set_rhs1 (use_stmt, unshare_expr (def_rhs)); > > > - gimple_assign_set_rhs_code (use_stmt, TREE_CODE (def_rhs)); > > > + rewrite_assign_addr (use_stmt_gsi, def_rhs); > > > + gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt); > > > return true; > > > } > > > > > > @@ -741,14 +782,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs, > > > if (forward_propagate_addr_expr (lhs, new_def_rhs, single_use_p)) > > > return true; > > > > > > - if (useless_type_conversion_p (TREE_TYPE (lhs), > > > - TREE_TYPE (new_def_rhs))) > > > - gimple_assign_set_rhs_with_ops (use_stmt_gsi, TREE_CODE (new_def_rhs), > > > - new_def_rhs); > > > - else if (is_gimple_min_invariant (new_def_rhs)) > > > - gimple_assign_set_rhs_with_ops (use_stmt_gsi, NOP_EXPR, new_def_rhs); > > > - else > > > - return false; > > > + rewrite_assign_addr (use_stmt_gsi, new_def_rhs); > > > gcc_assert (gsi_stmt (*use_stmt_gsi) == use_stmt); > > > update_stmt (use_stmt); > > > return true; > > > @@ -951,9 +985,7 @@ forward_propagate_addr_expr_1 (tree name, tree def_rhs, > > > unshare_expr (def_rhs), > > > fold_convert (ptr_type_node, > > > rhs2))); > > > - gimple_assign_set_rhs_from_tree (use_stmt_gsi, new_rhs); > > > - use_stmt = gsi_stmt (*use_stmt_gsi); > > > - update_stmt (use_stmt); > > > + rewrite_assign_addr (use_stmt_gsi, new_rhs); > > > > so you only do this after addr_expr forwarding but not on stmts in > > general? You could > > do it that way in the 2nd loop over the BB. > > > > > tidy_after_forward_propagate_addr (use_stmt); > > > return true; > > > } > > > -- > > > 2.17.1 > > >