> > The problem is that the patch fails testcases that assume we do such > > folding at parsing > > time. > > > > ./testsuite/gcc/gcc.sum:FAIL: gcc.dg/pr36901-1.c (test for excess errors) > > ./testsuite/gcc/gcc.sum:FAIL: gcc.dg/pr36901-2.c (test for excess errors) > > ./testsuite/gcc/gcc.sum:FAIL: gcc.dg/pr36901-3.c (test for excess errors) > > ./testsuite/gcc/gcc.sum:FAIL: gcc.dg/pr36901-4.c (test for excess errors) > > > > Here we accept the source as compile time constant while I think it is not: > > int sc = (&sc > 0); > > > > Does it seem resonable to turn those testcases into one testing for error > > and > > live with delaying the folding oppurtunities to early opts? They are now > > caught > > by ccp1 pass usually. > > IMHO all symbol visibility related foldings are very premature if done > in the frontends (well, most of fold-const.c is ...). Of course > everything depends on whether there exists a frontend that requires > these foldings for correctness ...
Yeah, in my testing it seems that C frontend do care in the testcase above - we used to accept code that does test nonzeroness of address as a constant, while we don't. Clang (IMO correctly) reject it. If we are OK with changing the bhaviour, I will just commit the patch and remove the testcase above (or turn it into error check) > > Personally I find "nonzero" ambiguous as it doesn't clearly state > it is about the symbols address rather than its value. I can change it to nonzero_address. It did not appear one might think about value stored in the symbol. Honza > > Richard. > > > > Honza > > > > * cgraph.h (symtab_node): Add method nonzero. > > (decl_in_symtab_p): Break out from ... > > (symtab_get_node): ... here. > > * symtab.c (symtab_node::nonzero): New method. > > * fold-const.c: Include cgraph.h > > (tree_single_nonzero_warnv_p): Use symtab for symbols. > > > > * testsuite/g++.dg/tree-ssa/nonzero-2.C: New testcase. > > * testsuite/g++.dg/tree-ssa/nonzero-1.C: New testcase. > > * testsuite/gcc.dg/tree-ssa/nonzero-1.c: New testcase. > > Index: cgraph.h > > =================================================================== > > --- cgraph.h (revision 211915) > > +++ cgraph.h (working copy) > > @@ -214,6 +214,9 @@ public: > > > > void set_init_priority (priority_type priority); > > priority_type get_init_priority (); > > + > > + /* Return true if symbol is known to be nonzero. */ > > + bool nonzero (); > > }; > > > > enum availability > > @@ -1068,6 +1077,17 @@ void varpool_remove_initializer (varpool > > /* In cgraph.c */ > > extern void change_decl_assembler_name (tree, tree); > > > > +/* Return true if DECL should have entry in symbol table if used. > > + Those are functions and static & external veriables*/ > > + > > +static bool > > +decl_in_symtab_p (const_tree decl) > > +{ > > + return (TREE_CODE (decl) == FUNCTION_DECL > > + || (TREE_CODE (decl) == VAR_DECL > > + && (TREE_STATIC (decl) || DECL_EXTERNAL (decl)))); > > +} > > + > > /* Return symbol table node associated with DECL, if any, > > and NULL otherwise. */ > > > > @@ -1075,12 +1095,7 @@ static inline symtab_node * > > symtab_get_node (const_tree decl) > > { > > #ifdef ENABLE_CHECKING > > - /* Check that we are called for sane type of object - functions > > - and static or external variables. */ > > - gcc_checking_assert (TREE_CODE (decl) == FUNCTION_DECL > > - || (TREE_CODE (decl) == VAR_DECL > > - && (TREE_STATIC (decl) || DECL_EXTERNAL (decl) > > - || in_lto_p))); > > + gcc_checking_assert (decl_in_symtab_p (decl)); > > /* Check that the mapping is sane - perhaps this check can go away, > > but at the moment frontends tends to corrupt the mapping by calling > > memcpy/memset on the tree nodes. */ > > Index: symtab.c > > =================================================================== > > --- symtab.c (revision 211915) > > +++ symtab.c (working copy) > > @@ -1574,4 +1574,67 @@ symtab_get_symbol_partitioning_class (sy > > > > return SYMBOL_PARTITION; > > } > > + > > +/* Return true when symbol is known to be non-zero. */ > > + > > +bool > > +symtab_node::nonzero () > > +{ > > + /* Weakrefs may be NULL when their target is not defined. */ > > + if (this->alias && this->weakref) > > + { > > + if (this->analyzed) > > + { > > + symtab_node *target = symtab_alias_ultimate_target (this); > > + > > + if (target->alias && target->weakref) > > + return false; > > + /* We can not recurse to target::nonzero. It is possible that the > > + target is used only via the alias. > > + We may walk references and look for strong use, but we do not know > > + if this strong use will survive to final binary, so be > > + conservative here. > > + ??? Maybe we could do the lookup during late optimization that > > + could be useful to eliminate the NULL pointer checks in LTO > > + programs. */ > > + if (target->definition && !DECL_EXTERNAL (target->decl)) > > + return true; > > + if (target->resolution != LDPR_UNKNOWN > > + && target->resolution != LDPR_UNDEF > > + && flag_delete_null_pointer_checks) > > + return true; > > + return false; > > + } > > + else > > + return false; > > + } > > + > > + /* With !flag_delete_null_pointer_checks we assume that symbols may > > + bind to NULL. This is on by default on embedded targets only. > > + > > + Otherwise all non-WEAK symbols must be defined and thus non-NULL or > > + linking fails. Important case of WEAK we want to do well are comdats. > > + Those are handled by later check for definition. > > + > > + When parsing, beware the cases when WEAK attribute is added later. */ > > + if (!DECL_WEAK (this->decl) > > + && flag_delete_null_pointer_checks > > + && cgraph_state > CGRAPH_STATE_PARSING) > > + return true; > > + > > + /* If target is defined and not extern, we know it will be output and > > thus > > + it will bind to non-NULL. > > + Play safe for flag_delete_null_pointer_checks where weak definition > > maye > > + be re-defined by NULL. */ > > + if (this->definition && !DECL_EXTERNAL (this->decl) > > + && (flag_delete_null_pointer_checks || !DECL_WEAK (this->decl))) > > + return true; > > + > > + /* As the last resort, check the resolution info. */ > > + if (this->resolution != LDPR_UNKNOWN > > + && this->resolution != LDPR_UNDEF > > + && flag_delete_null_pointer_checks) > > + return true; > > + return false; > > +} > > #include "gt-symtab.h" > > Index: fold-const.c > > =================================================================== > > --- fold-const.c (revision 211915) > > +++ fold-const.c (working copy) > > @@ -69,6 +69,7 @@ along with GCC; see the file COPYING3. > > #include "tree-dfa.h" > > #include "hash-table.h" /* Required for ENABLE_FOLD_CHECKING. */ > > #include "builtins.h" > > +#include "cgraph.h" > > > > /* Nonzero if we are folding constants inside an initializer; zero > > otherwise. */ > > @@ -16032,21 +16033,33 @@ tree_single_nonzero_warnv_p (tree t, boo > > case ADDR_EXPR: > > { > > tree base = TREE_OPERAND (t, 0); > > + > > if (!DECL_P (base)) > > base = get_base_address (base); > > > > if (!base) > > return false; > > > > - /* Weak declarations may link to NULL. Other things may also be NULL > > - so protect with -fdelete-null-pointer-checks; but not variables > > - allocated on the stack. */ > > + /* For objects in symbol table check if we know they are non-zero. > > + Don't do anything for variables and functions before symtab is built; > > + it is quite possible that they will be declared weak later. */ > > + if (DECL_P (base) && decl_in_symtab_p (base)) > > + { > > + struct symtab_node *symbol; > > + > > + symbol = symtab_get_node (base); > > + if (symbol) > > + return symbol->nonzero (); > > + else > > + return false; > > + } > > + > > + /* Function local objects are never NULL. */ > > if (DECL_P (base) > > - && (flag_delete_null_pointer_checks > > - || (DECL_CONTEXT (base) > > - && TREE_CODE (DECL_CONTEXT (base)) == FUNCTION_DECL > > - && auto_var_in_fn_p (base, DECL_CONTEXT (base))))) > > - return !VAR_OR_FUNCTION_DECL_P (base) || !DECL_WEAK (base); > > + && (DECL_CONTEXT (base) > > + && TREE_CODE (DECL_CONTEXT (base)) == FUNCTION_DECL > > + && auto_var_in_fn_p (base, DECL_CONTEXT (base)))) > > + return true; > > > > /* Constants are never weak. */ > > if (CONSTANT_CLASS_P (base)) > > Index: testsuite/gcc.dg/tree-ssa/nonzero-1.c > > =================================================================== > > --- testsuite/gcc.dg/tree-ssa/nonzero-1.c (revision 0) > > +++ testsuite/gcc.dg/tree-ssa/nonzero-1.c (revision 0) > > @@ -0,0 +1,11 @@ > > +/* { dg-do compile } */ > > +/* { dg-options "-O2 -fdump-tree-optimized" } */ > > +extern int a; > > +t() > > +{ > > + return &a!=0; > > +} > > +extern int a __attribute__ ((weak)); > > + > > +/* { dg-final { scan-tree-dump-not "return 1" "optimized"} } */ > > +/* { dg-final { cleanup-tree-dump "optimized" } } */ > > Index: testsuite/g++.dg/tree-ssa/nonzero-1.C > > =================================================================== > > --- testsuite/g++.dg/tree-ssa/nonzero-1.C (revision 0) > > +++ testsuite/g++.dg/tree-ssa/nonzero-1.C (revision 0) > > @@ -0,0 +1,12 @@ > > +/* { dg-do compile } */ > > +/* { dg-options "-O2 -fdump-tree-ccp1" } */ > > +inline void t() > > +{ > > +} > > +int m() > > +{ > > + void *q = (void *)&t; > > + return q != 0; > > +} > > +/* { dg-final { scan-tree-dump "return 1" "ccp1"} } */ > > +/* { dg-final { cleanup-tree-dump "ccp1" } } */ > > Index: testsuite/g++.dg/tree-ssa/nonzero-2.C > > =================================================================== > > --- testsuite/g++.dg/tree-ssa/nonzero-2.C (revision 0) > > +++ testsuite/g++.dg/tree-ssa/nonzero-2.C (revision 0) > > @@ -0,0 +1,16 @@ > > +/* { dg-do compile } */ > > +/* { dg-options "-O2 -fdump-tree-ccp1 -fdelete-null-pointer-checks" } */ > > +struct t > > +{ > > + static inline void tt() > > + { > > + } > > + virtual void q(); > > +}; > > +int m() > > +{ > > + void *q = (void *)&t::tt; > > + return q != 0; > > +} > > +/* { dg-final { scan-tree-dump "return 1" "ccp1"} } */ > > +/* { dg-final { cleanup-tree-dump "ccp1" } } */ > > > > > > -- > Richard Biener <rguent...@suse.de> > SUSE / SUSE Labs > SUSE LINUX Products GmbH - Nuernberg - AG Nuernberg - HRB 16746 > GF: Jeff Hawn, Jennifer Guild, Felix Imend"orffer