[PATCH] Fix PR/63841: empty constructor doesn't zero-initialize
Richard Biener
richard.guenther@gmail.com
Thu Nov 13 14:32:00 GMT 2014
On Thu, Nov 13, 2014 at 3:20 PM, Teresa Johnson <tejohnson@google.com> wrote:
> Here is the new patch. Bootstrapped and tested on
> x86_64-unknown-linux-gnu. OK for trunk?
Ok for trunk and branches.
Thanks,
Richard.
> Thanks,
> Teresa
>
> 2014-11-13 <tejohnson@google.com>
>
> gcc:
> PR tree-optimization/63841
> * tree.c (initializer_zerop): A constructor with no elements
> does not zero initialize.
>
> gcc/testsuite:
> PR tree-optimization/63841
> * g++.dg/tree-ssa/pr63841.C: New test.
>
> Index: tree.c
> ===================================================================
> --- tree.c (revision 217190)
> +++ tree.c (working copy)
> @@ -10330,6 +10330,8 @@ initializer_zerop (const_tree init)
> {
> unsigned HOST_WIDE_INT idx;
>
> + if (TREE_CLOBBER_P (init))
> + return false;
> FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (init), idx, elt)
> if (!initializer_zerop (elt))
> return false;
> Index: testsuite/g++.dg/tree-ssa/pr63841.C
> ===================================================================
> --- testsuite/g++.dg/tree-ssa/pr63841.C (revision 0)
> +++ testsuite/g++.dg/tree-ssa/pr63841.C (working copy)
> @@ -0,0 +1,38 @@
> +/* { dg-do run } */
> +/* { dg-options "-O2" } */
> +
> +#include <cstdio>
> +#include <string>
> +
> +std::string __attribute__ ((noinline)) comp_test_write() {
> + std::string data;
> +
> + for (int i = 0; i < 2; ++i) {
> + char b = 1 >> (i * 8);
> + data.append(&b, 1);
> + }
> +
> + return data;
> +}
> +
> +std::string __attribute__ ((noinline)) comp_test_write_good() {
> + std::string data;
> +
> + char b;
> + for (int i = 0; i < 2; ++i) {
> + b = 1 >> (i * 8);
> + data.append(&b, 1);
> + }
> +
> + return data;
> +}
> +
> +int main() {
> + std::string good = comp_test_write_good();
> + printf("expected: %hx\n", *(short*)good.c_str());
> +
> + std::string bad = comp_test_write();
> + printf("got: %hx\n", *(short*)bad.c_str());
> +
> + return good != bad;
> +}
>
> On Wed, Nov 12, 2014 at 9:40 PM, Andrew Pinski <pinskia@gmail.com> wrote:
>> On Wed, Nov 12, 2014 at 9:38 PM, Teresa Johnson <tejohnson@google.com> wrote:
>>> On Wed, Nov 12, 2014 at 9:30 PM, Andrew Pinski <pinskia@gmail.com> wrote:
>>>> On Wed, Nov 12, 2014 at 9:25 PM, Teresa Johnson <tejohnson@google.com> wrote:
>>>>> Added testcase. Here is the new patch:
>>>>>
>>>>> 2014-11-12 <tejohnson@google.com>
>>>>>
>>>>> gcc:
>>>>> PR tree-optimization/63841
>>>>> * tree.c (initializer_zerop): A constructor with no elements
>>>>> does not zero initialize.
>>>>
>>>> Actually an empty constructor does zero initialize. A clobber does not.
>>>
>>> Ok, thanks, I wasn't sure.
>>>
>>>>
>>>> The check you want is TREE_CLOBBER_P instead.
>>>
>>> So in initializer_zerop, a constructor that is a TREE_CLOBBER_P would
>>> return false, right? I will make that change and retest.
>>
>> Yes that is correct. Note TREE_CLOBBER_P already checks if it is an
>> constructor.
>>
>> Thanks,
>> Andrew
>>
>>>
>>> Thanks,
>>> Teresa
>>>
>>>>
>>>> Thanks,
>>>> Andrew
>>>>
>>>>
>>>>>
>>>>> gcc/testsuite:
>>>>> * g++.dg/tree-ssa/pr63841.C: New test.
>>>>>
>>>>> Index: tree.c
>>>>> ===================================================================
>>>>> --- tree.c (revision 217190)
>>>>> +++ tree.c (working copy)
>>>>> @@ -10330,6 +10330,8 @@ initializer_zerop (const_tree init)
>>>>> {
>>>>> unsigned HOST_WIDE_INT idx;
>>>>>
>>>>> + if (!CONSTRUCTOR_NELTS (init))
>>>>> + return false;
>>>>> FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (init), idx, elt)
>>>>> if (!initializer_zerop (elt))
>>>>> return false;
>>>>> Index: testsuite/g++.dg/tree-ssa/pr63841.C
>>>>> ===================================================================
>>>>> --- testsuite/g++.dg/tree-ssa/pr63841.C (revision 0)
>>>>> +++ testsuite/g++.dg/tree-ssa/pr63841.C (working copy)
>>>>> @@ -0,0 +1,38 @@
>>>>> +/* { dg-do run } */
>>>>> +/* { dg-options "-O2" } */
>>>>> +
>>>>> +#include <cstdio>
>>>>> +#include <string>
>>>>> +
>>>>> +std::string __attribute__ ((noinline)) comp_test_write() {
>>>>> + std::string data;
>>>>> +
>>>>> + for (int i = 0; i < 2; ++i) {
>>>>> + char b = 1 >> (i * 8);
>>>>> + data.append(&b, 1);
>>>>> + }
>>>>> +
>>>>> + return data;
>>>>> +}
>>>>> +
>>>>> +std::string __attribute__ ((noinline)) comp_test_write_good() {
>>>>> + std::string data;
>>>>> +
>>>>> + char b;
>>>>> + for (int i = 0; i < 2; ++i) {
>>>>> + b = 1 >> (i * 8);
>>>>> + data.append(&b, 1);
>>>>> + }
>>>>> +
>>>>> + return data;
>>>>> +}
>>>>> +
>>>>> +int main() {
>>>>> + std::string good = comp_test_write_good();
>>>>> + printf("expected: %hx\n", *(short*)good.c_str());
>>>>> +
>>>>> + std::string bad = comp_test_write();
>>>>> + printf("got: %hx\n", *(short*)bad.c_str());
>>>>> +
>>>>> + return good != bad;
>>>>> +}
>>>>>
>>>>> On Wed, Nov 12, 2014 at 2:17 PM, Xinliang David Li <davidxl@google.com> wrote:
>>>>>> missing test case?
>>>>>>
>>>>>> David
>>>>>>
>>>>>> On Wed, Nov 12, 2014 at 2:13 PM, Teresa Johnson <tejohnson@google.com> wrote:
>>>>>>> This patch fixes an issue where tree-strlen was incorrectly removing a
>>>>>>> store of 0 into a string because it thought a prior CLOBBER (which is
>>>>>>> an empty constructor with no elements) was zero-initializing the
>>>>>>> string.
>>>>>>>
>>>>>>> Bootstrapped and tested on x86_64-unknown-linux-gnu. OK for trunk?
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Teresa
>>>>>>>
>>>>>>> 2014-11-12 <tejohnson@google.com>
>>>>>>>
>>>>>>> PR tree-optimization/63841
>>>>>>> * tree.c (initializer_zerop): A constructor with no elements
>>>>>>> does not zero initialize.
>>>>>>>
>>>>>>> Index: tree.c
>>>>>>> ===================================================================
>>>>>>> --- tree.c (revision 217190)
>>>>>>> +++ tree.c (working copy)
>>>>>>> @@ -10330,6 +10330,8 @@ initializer_zerop (const_tree init)
>>>>>>> {
>>>>>>> unsigned HOST_WIDE_INT idx;
>>>>>>>
>>>>>>> + if (!CONSTRUCTOR_NELTS (init))
>>>>>>> + return false;
>>>>>>> FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (init), idx, elt)
>>>>>>> if (!initializer_zerop (elt))
>>>>>>> return false;
>>>>>>>
>>>>>>>
>>>>>>> --
>>>>>>> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413
>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413
>>>
>>>
>>>
>>> --
>>> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413
>
>
>
> --
> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413
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