On a tree-ssa build pulled today, I get "pure virtual method called" (and execution aborts) if I attempt to call a method on a static_casted pointer. I believe this regressed within the past few weeks. The error occurs with -O2, but not with -O. gcc build details: $ c++ -v Reading specs from /usr/gcc-ssa/lib/gcc/i686-pc-linux-gnu/3.5-tree-ssa/specs Configured with: ../gcc/configure --prefix=/usr/gcc-ssa --enable-shared --enable-threads=posix --with-system-zlib --enable-__cxa_atexit --host=i686-pc-linux-gnu --enable-languages=c,c++ --disable-checking Thread model: posix gcc version 3.5-tree-ssa 20040309 (merged 20040307)
Created attachment 5891 [details] testcase testcase output: $ c++ -O2 -o test_virt_cast test_virt_cast.cpp $ ./test_virt_cast pure virtual method called terminate called without an active exception Aborted
Confirmed, this is an aliasing problem (I think caused by the C++ front-end).
The issue I think is that the structs are not marked as they can alias each other.
Created attachment 5927 [details] Patch to mark VA_ARG_EXPR operands volatile as they are created
dammit! Bugzilla tricked me again and I attached a patch to the wrong case. Please disregard
Subject: Re: [tree-ssa] "pure virtual method called" error when calling a method on a static_casted object On Wed, 2004-03-10 at 14:01, pinskia at gcc dot gnu dot org wrote: > ------- Additional Comments From pinskia at gcc dot gnu dot org 2004-03-10 19:01 ------- > The issue I think is that the structs are not marked as they can alias each other. > Indeed. The problem occurs when we replace the RHS of (3) with &_ZTV4IFoo<D1485>[2] 1. this<D1553>_6->_vptr.IFoo<D1483> = &_ZTV4IFoo<D1485>[2]; 2. this<D1550>_4->_vptr.IFoo<D1511> = &_ZTV3Bar<D1512>[2]; 3. T.3<D1532>_10 = this<D1553>_6->_vptr.IFoo<D1483>; 4. T.4<D1533>_11 = *T.3<D1532>_10; 5. # VUSE <_ZTV4IFoo_1>; 6. # VUSE <_ZTV3Bar_2>; 7. T.4_11 (this<D1553>_6); The alias pass was not computing type aliases properly for this<D1553> and this<D1550> for two reasons: * Variables _ZTV4IFoo<D1485> and _ZTV3Bar<D1512 are read-only, so they were being ignored. However, ignoring them meant that the alias sets for this<D1553> and this<D1550> were not being populated, therefore the two memory tags were not found to conflict, allowing DOM to propagate (1) into (3). * The sub-type checking in may_alias_p was not computing the right pointer-to type for ARRAY_TYPEs. Bootstrapped and tested on x86, x86-64 and ia64. Diego. * tree-ssa-alias.c (compute_flow_insensitive_aliasing): Do not ignore read-only variables. (may_alias_p): Fix pointer-to-var calculation when 'var' is an array. testsuite/ChangeLog.tree-ssa: * g++.dg/tree-ssa/20040317-1.C: New test. Index: tree-ssa-alias.c =================================================================== RCS file: /cvs/gcc/gcc/gcc/Attic/tree-ssa-alias.c,v retrieving revision 1.1.2.12 diff -d -c -p -d -u -p -r1.1.2.12 tree-ssa-alias.c --- tree-ssa-alias.c 16 Mar 2004 22:31:55 -0000 1.1.2.12 +++ tree-ssa-alias.c 17 Mar 2004 19:17:31 -0000 @@ -797,10 +797,6 @@ compute_flow_insensitive_aliasing (struc if (!tag_stored_p && !var_stored_p) continue; - /* Skip memory tags which are written if the variable is readonly. */ - if (tag_stored_p && TREE_READONLY (var)) - continue; - if (may_alias_p (p_map->var, p_map->set, var, v_map->set)) { size_t num_tag_refs = ai->num_references[tag_ann->uid]; @@ -1337,7 +1333,12 @@ may_alias_p (tree ptr, HOST_WIDE_INT mem if (AGGREGATE_TYPE_P (TREE_TYPE (mem)) || AGGREGATE_TYPE_P (TREE_TYPE (var))) { - tree ptr_to_var = TYPE_POINTER_TO (TREE_TYPE (var)); + tree ptr_to_var; + + if (TREE_CODE (TREE_TYPE (var)) == ARRAY_TYPE) + ptr_to_var = TYPE_POINTER_TO (TREE_TYPE (TREE_TYPE (var))); + else + ptr_to_var = TYPE_POINTER_TO (TREE_TYPE (var)); /* If no pointer-to VAR exists, then MEM can't alias VAR. */ if (ptr_to_var == NULL_TREE) Index: testsuite/g++.dg/tree-ssa/20040317-1.C =================================================================== RCS file: testsuite/g++.dg/tree-ssa/20040317-1.C diff -N testsuite/g++.dg/tree-ssa/20040317-1.C --- /dev/null 1 Jan 1970 00:00:00 -0000 +++ testsuite/g++.dg/tree-ssa/20040317-1.C 17 Mar 2004 19:17:31 -0000 @@ -0,0 +1,38 @@ +/* { dg-do run } */ +/* { dg-options "-O2" } */ + +/* Test provided by Brian Ryner in PR 14511. The alias analyzer was + not handling structures containing arrays properly. In this case, + the static cast was introducing two assignments of the form + + this_6->_vptr.IFoo = &_ZTV4IFoo[2]; + this_4->_vptr.IFoo = &_ZTV3Bar[2]; + + which were not considered to alias each other because the alias + analyzer was not computing a proper pointer to array elements. + Another related bug was the type based alias analyzer not computing + alias relations to _ZTV4IFoo and _ZTV3Bar. Since those variables + are read-only, it was disregarding alias information for them. + So, the memory tags for the two 'this' variables were not being + marked as aliased with these variables. Resulting in the two + assignments not aliasing each other. + + This was causing the optimizers to generate a call to the virtual + method Foo() instead of the overloaded version. */ + +struct IFoo +{ + virtual void Foo() = 0; +}; + +struct Bar : IFoo +{ + void Foo() { } +}; + +int main(int argc, char **argv) +{ + Bar* b = new Bar(); + static_cast<IFoo*>(b)->Foo(); + return 0; +}
Subject: Bug 14511 CVSROOT: /cvs/gcc Module name: gcc Branch: tree-ssa-20020619-branch Changes by: dnovillo@gcc.gnu.org 2004-03-17 19:44:36 Modified files: gcc : ChangeLog.tree-ssa tree-ssa-alias.c gcc/testsuite : ChangeLog.tree-ssa gcc/testsuite/g++.dg: README Added files: gcc/testsuite/g++.dg/tree-ssa: 20040317-1.C Log message: PR optimization/14511 * tree-ssa-alias.c (compute_flow_insensitive_aliasing): Do not ignore read-only variables. (may_alias_p): Fix pointer-to-var calculation when 'var' is an array. Patches: http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/ChangeLog.tree-ssa.diff?cvsroot=gcc&only_with_tag=tree-ssa-20020619-branch&r1=1.1.2.1278&r2=1.1.2.1279 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/tree-ssa-alias.c.diff?cvsroot=gcc&only_with_tag=tree-ssa-20020619-branch&r1=1.1.2.12&r2=1.1.2.13 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.tree-ssa.diff?cvsroot=gcc&only_with_tag=tree-ssa-20020619-branch&r1=1.1.2.190&r2=1.1.2.191 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/README.diff?cvsroot=gcc&only_with_tag=tree-ssa-20020619-branch&r1=1.2.14.4&r2=1.2.14.5 http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/tree-ssa/20040317-1.C.diff?cvsroot=gcc&only_with_tag=tree-ssa-20020619-branch&r1=NONE&r2=1.1.2.1
Fixed.