operator new returns nonzero
Gabriel Dos Reis
gdr@integrable-solutions.net
Mon Sep 9 12:49:00 GMT 2013
On Mon, Sep 9, 2013 at 4:06 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Sat, Sep 7, 2013 at 11:00 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
>> On Sat, 7 Sep 2013, Mike Stump wrote:
>>
>>> On Sep 7, 2013, at 12:27 PM, Marc Glisse <marc.glisse@inria.fr> wrote:
>>>>
>>>> Now flag_check_new should probably disable this optimization…
>>>
>>>
>>> Yes, this why my point.
>>
>>
>> Ok, here it is (again, no proper testing until bootstrap is fixed)
>
> I wonder what happens on targets where 0 is a valid address of an object
> (stated by !flag_delete_null_pointer_checks)?
We should distinguish between front-end notion of null pointer,
and backend notion of address zero. The language, and therefore
the front-end, does not allow an object to have 'this' value to be
a null pointer, nor does is allow 'operator new' to return null pointer.
Consequently, if we have a target (which ones?) where zero is
a valid address for an object, that target should take precaution
to satisfy the requirement of the language.
-- Gaby
>
> Richard.
>
>>
>> 2013-09-07 Marc Glisse <marc.glisse@inria.fr>
>>
>> PR c++/19476
>> gcc/
>> * fold-const.c (tree_expr_nonzero_warnv_p): Handle operator new.
>> * tree-vrp.c (gimple_stmt_nonzero_warnv_p,
>> stmt_interesting_for_vrp):
>> Likewise.
>> (vrp_visit_stmt): Remove duplicated code.
>>
>> gcc/testsuite/
>> * g++.dg/tree-ssa/pr19476-1.C: New file.
>> * g++.dg/tree-ssa/pr19476-2.C: Likewise.
>> * g++.dg/tree-ssa/pr19476-3.C: Likewise.
>>
>> --
>> Marc Glisse
>> Index: testsuite/g++.dg/tree-ssa/pr19476-1.C
>> ===================================================================
>> --- testsuite/g++.dg/tree-ssa/pr19476-1.C (revision 0)
>> +++ testsuite/g++.dg/tree-ssa/pr19476-1.C (revision 0)
>> @@ -0,0 +1,15 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O -fdump-tree-ccp1" } */
>> +
>> +#include <new>
>> +
>> +int f(){
>> + return 33 + (0 == new(std::nothrow) int);
>> +}
>> +int g(){
>> + return 42 + (0 == new int[50]);
>> +}
>> +
>> +/* { dg-final { scan-tree-dump "return 42" "ccp1" } } */
>> +/* { dg-final { scan-tree-dump-not "return 33" "ccp1" } } */
>> +/* { dg-final { cleanup-tree-dump "ccp1" } } */
>>
>> Property changes on: testsuite/g++.dg/tree-ssa/pr19476-1.C
>> ___________________________________________________________________
>> Added: svn:keywords
>> + Author Date Id Revision URL
>> Added: svn:eol-style
>> + native
>>
>> Index: testsuite/g++.dg/tree-ssa/pr19476-2.C
>> ===================================================================
>> --- testsuite/g++.dg/tree-ssa/pr19476-2.C (revision 0)
>> +++ testsuite/g++.dg/tree-ssa/pr19476-2.C (revision 0)
>> @@ -0,0 +1,17 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -fdump-tree-optimized" } */
>> +
>> +#include <new>
>> +
>> +int f(){
>> + int *p = new(std::nothrow) int;
>> + return 33 + (0 == p);
>> +}
>> +int g(){
>> + int *p = new int[50];
>> + return 42 + (0 == p);
>> +}
>> +
>> +/* { dg-final { scan-tree-dump "return 42" "optimized" } } */
>> +/* { dg-final { scan-tree-dump-not "return 33" "optimized" } } */
>> +/* { dg-final { cleanup-tree-dump "optimized" } } */
>>
>> Property changes on: testsuite/g++.dg/tree-ssa/pr19476-2.C
>> ___________________________________________________________________
>> Added: svn:keywords
>> + Author Date Id Revision URL
>> Added: svn:eol-style
>> + native
>>
>> Index: testsuite/g++.dg/tree-ssa/pr19476-3.C
>> ===================================================================
>> --- testsuite/g++.dg/tree-ssa/pr19476-3.C (revision 0)
>> +++ testsuite/g++.dg/tree-ssa/pr19476-3.C (revision 0)
>> @@ -0,0 +1,11 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O3 -fcheck-new -fdump-tree-optimized" } */
>> +
>> +#include <new>
>> +
>> +int g(){
>> + return 42 + (0 == new int);
>> +}
>> +
>> +/* { dg-final { scan-tree-dump-not "return 42" "optimized" } } */
>> +/* { dg-final { cleanup-tree-dump "optimized" } } */
>>
>> Property changes on: testsuite/g++.dg/tree-ssa/pr19476-3.C
>> ___________________________________________________________________
>> Added: svn:keywords
>> + Author Date Id Revision URL
>> Added: svn:eol-style
>> + native
>>
>> Index: fold-const.c
>> ===================================================================
>> --- fold-const.c (revision 202351)
>> +++ fold-const.c (working copy)
>> @@ -16171,21 +16171,31 @@ tree_expr_nonzero_warnv_p (tree t, bool
>> case MODIFY_EXPR:
>> case BIND_EXPR:
>> return tree_expr_nonzero_warnv_p (TREE_OPERAND (t, 1),
>> strict_overflow_p);
>>
>> case SAVE_EXPR:
>> return tree_expr_nonzero_warnv_p (TREE_OPERAND (t, 0),
>> strict_overflow_p);
>>
>> case CALL_EXPR:
>> - return alloca_call_p (t);
>> + {
>> + tree fn = CALL_EXPR_FN (t);
>> + if (TREE_CODE (fn) != ADDR_EXPR) return false;
>> + tree fndecl = TREE_OPERAND (fn, 0);
>> + if (TREE_CODE (fndecl) != FUNCTION_DECL) return false;
>> + if (!flag_check_new
>> + && DECL_IS_OPERATOR_NEW (fndecl)
>> + && !TREE_NOTHROW (fndecl))
>> + return true;
>> + return alloca_call_p (t);
>> + }
>>
>> default:
>> break;
>> }
>> return false;
>> }
>>
>> /* Return true when T is an address and is known to be nonzero.
>> Handle warnings about undefined signed overflow. */
>>
>> Index: tree-vrp.c
>> ===================================================================
>> --- tree-vrp.c (revision 202351)
>> +++ tree-vrp.c (working copy)
>> @@ -1047,21 +1047,29 @@ gimple_assign_nonzero_warnv_p (gimple st
>> *STRICT_OVERFLOW_P.*/
>>
>> static bool
>> gimple_stmt_nonzero_warnv_p (gimple stmt, bool *strict_overflow_p)
>> {
>> switch (gimple_code (stmt))
>> {
>> case GIMPLE_ASSIGN:
>> return gimple_assign_nonzero_warnv_p (stmt, strict_overflow_p);
>> case GIMPLE_CALL:
>> - return gimple_alloca_call_p (stmt);
>> + {
>> + tree fndecl = gimple_call_fndecl (stmt);
>> + if (!fndecl) return false;
>> + if (!flag_check_new
>> + && DECL_IS_OPERATOR_NEW (fndecl)
>> + && !TREE_NOTHROW (fndecl))
>> + return true;
>> + return gimple_alloca_call_p (stmt);
>> + }
>> default:
>> gcc_unreachable ();
>> }
>> }
>>
>> /* Like tree_expr_nonzero_warnv_p, but this function uses value ranges
>> obtained so far. */
>>
>> static bool
>> vrp_stmt_computes_nonzero (gimple stmt, bool *strict_overflow_p)
>> @@ -6486,21 +6494,22 @@ stmt_interesting_for_vrp (gimple stmt)
>> tree lhs = gimple_get_lhs (stmt);
>>
>> /* In general, assignments with virtual operands are not useful
>> for deriving ranges, with the obvious exception of calls to
>> builtin functions. */
>> if (lhs && TREE_CODE (lhs) == SSA_NAME
>> && (INTEGRAL_TYPE_P (TREE_TYPE (lhs))
>> || POINTER_TYPE_P (TREE_TYPE (lhs)))
>> && ((is_gimple_call (stmt)
>> && gimple_call_fndecl (stmt) != NULL_TREE
>> - && DECL_BUILT_IN (gimple_call_fndecl (stmt)))
>> + && (DECL_BUILT_IN (gimple_call_fndecl (stmt))
>> + || DECL_IS_OPERATOR_NEW (gimple_call_fndecl (stmt))))
>> || !gimple_vuse (stmt)))
>> return true;
>> }
>> else if (gimple_code (stmt) == GIMPLE_COND
>> || gimple_code (stmt) == GIMPLE_SWITCH)
>> return true;
>>
>> return false;
>> }
>>
>> @@ -7407,30 +7416,21 @@ vrp_visit_stmt (gimple stmt, edge *taken
>> if (dump_file && (dump_flags & TDF_DETAILS))
>> {
>> fprintf (dump_file, "\nVisiting statement:\n");
>> print_gimple_stmt (dump_file, stmt, 0, dump_flags);
>> fprintf (dump_file, "\n");
>> }
>>
>> if (!stmt_interesting_for_vrp (stmt))
>> gcc_assert (stmt_ends_bb_p (stmt));
>> else if (is_gimple_assign (stmt) || is_gimple_call (stmt))
>> - {
>> - /* In general, assignments with virtual operands are not useful
>> - for deriving ranges, with the obvious exception of calls to
>> - builtin functions. */
>> - if ((is_gimple_call (stmt)
>> - && gimple_call_fndecl (stmt) != NULL_TREE
>> - && DECL_BUILT_IN (gimple_call_fndecl (stmt)))
>> - || !gimple_vuse (stmt))
>> - return vrp_visit_assignment_or_call (stmt, output_p);
>> - }
>> + return vrp_visit_assignment_or_call (stmt, output_p);
>> else if (gimple_code (stmt) == GIMPLE_COND)
>> return vrp_visit_cond_stmt (stmt, taken_edge_p);
>> else if (gimple_code (stmt) == GIMPLE_SWITCH)
>> return vrp_visit_switch_stmt (stmt, taken_edge_p);
>>
>> /* All other statements produce nothing of interest for VRP, so mark
>> their outputs varying and prevent further simulation. */
>> FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_DEF)
>> set_value_range_to_varying (get_value_range (def));
>>
>>
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