From 926f5059bb8d295e2b68cea7c9af53606946eb1a Mon Sep 17 00:00:00 2001 From: Richard Biener Date: Tue, 6 Dec 2022 10:12:01 +0100 Subject: [PATCH] tree-optimization/104475 - improve access diagnostics When we end up isolating a nullptr path it happens we diagnose accesses to offsetted nullptr objects. The current diagnostics have no good indication that this happens so the following records the fact that our heuristic detected a nullptr based access in the access_ref structure and sets up diagnostics to inform of that detail. The diagnostic itself could probably be improved here but its API is twisted and the necessary object isn't passed around. Instead of just ...bits/atomic_base.h:655:34: warning: 'unsigned int __atomic_fetch_and_4(volatile void*, unsigned int, int)' writing 4 bytes into a region of size 0 overflows the destination [-Wstringop-overflow=] we now add In member function 'void QFutureInterfaceBase::setThrottled(bool)': cc1plus: note: destination object is likely at address zero PR tree-optimization/104475 * pointer-query.h (access_ref::ref_nullptr_p): New flag. * pointer-query.cc (access_ref::access_ref): Initialize ref_nullptr_p. (compute_objsize_r): Set ref_nullptr_p if we treat it that way. (access_ref::inform_access): If ref was treated as nullptr based, indicate that. --- gcc/pointer-query.cc | 20 ++++++++++++++++---- gcc/pointer-query.h | 5 ++++- 2 files changed, 20 insertions(+), 5 deletions(-) diff --git a/gcc/pointer-query.cc b/gcc/pointer-query.cc index 95565fd..ea6ca68 100644 --- a/gcc/pointer-query.cc +++ b/gcc/pointer-query.cc @@ -600,8 +600,8 @@ gimple_parm_array_size (tree ptr, wide_int rng[2], /* Initialize the object. */ access_ref::access_ref () - : ref (), eval ([](tree x){ return x; }), deref (), trail1special (true), - base0 (true), parmarray () + : ref (), eval ([](tree x){ return x; }), deref (), ref_nullptr_p (false), + trail1special (true), base0 (true), parmarray () { /* Set to valid. */ offrng[0] = offrng[1] = 0; @@ -1193,7 +1193,16 @@ access_ref::inform_access (access_mode mode, int ostype /* = 1 */) const loc = EXPR_LOCATION (ref); else if (TREE_CODE (ref) != IDENTIFIER_NODE && TREE_CODE (ref) != SSA_NAME) - return; + { + if (TREE_CODE (ref) == INTEGER_CST && ref_nullptr_p) + { + if (mode == access_read_write || mode == access_write_only) + inform (loc, "destination object is likely at address zero"); + else + inform (loc, "source object is likely at address zero"); + } + return; + } if (mode == access_read_write || mode == access_write_only) { @@ -2280,7 +2289,10 @@ compute_objsize_r (tree ptr, gimple *stmt, bool addr, int ostype, if (targetm.addr_space.zero_address_valid (as)) pref->set_max_size_range (); else - pref->sizrng[0] = pref->sizrng[1] = 0; + { + pref->sizrng[0] = pref->sizrng[1] = 0; + pref->ref_nullptr_p = true; + } } else pref->sizrng[0] = pref->sizrng[1] = 0; diff --git a/gcc/pointer-query.h b/gcc/pointer-query.h index 801a240..19a6f15 100644 --- a/gcc/pointer-query.h +++ b/gcc/pointer-query.h @@ -88,7 +88,7 @@ struct access_ref argument to the minimum. */ offset_int size_remaining (offset_int * = nullptr) const; -/* Return true if the offset and object size are in range for SIZE. */ + /* Return true if the offset and object size are in range for SIZE. */ bool offset_in_range (const offset_int &) const; /* Return true if *THIS is an access to a declared object. */ @@ -141,6 +141,9 @@ struct access_ref /* Positive when REF is dereferenced, negative when its address is taken. */ int deref; + /* The following indicates if heuristics interpreted 'ref' is interpreted + as (offsetted) nullptr. */ + bool ref_nullptr_p; /* Set if trailing one-element arrays should be treated as flexible array members. */ bool trail1special; -- 2.7.4