Use ad hoc itoa function instead of OS::SNPrintF when serializing heap snapshots

Switching to a custom itoa implementation reduces serialization time at least by the factor of 2.
Committed: https://code.google.com/p/v8/source/detail?r=11223

[mnaganov (inactive), 2012-04-04 10:03:30]

https://chromiumcodereview.appspot.com/9950146/diff/1/src/profile-generator.cc
File src/profile-generator.cc (right):

https://chromiumcodereview.appspot.com/9950146/diff/1/src/profile-generator.c...
src/profile-generator.cc:3511: static char* itoa(int value, char* buffer) {
Have you tried IntToCString? It uses Vector, which has overrun asserts in debug
mode.

[alexeif, 2012-04-04 11:20:49]

What is the performance impact of the change?

https://chromiumcodereview.appspot.com/9950146/diff/1/src/profile-generator.cc
File src/profile-generator.cc (right):

https://chromiumcodereview.appspot.com/9950146/diff/1/src/profile-generator.c...
src/profile-generator.cc:3511: static char* itoa(int value, char* buffer) {
On 2012/04/04 10:03:31, Mikhail Naganov (Chromium) wrote:
> Have you tried IntToCString? It uses Vector, which has overrun asserts in
debug
> mode.
I have more concerns regarding the checks in release mode.

https://chromiumcodereview.appspot.com/9950146/diff/1/src/profile-generator.c...
src/profile-generator.cc:3568: STATIC_CHECK(sizeof(int) ==
sizeof(entry->type()));  // NOLINT
If you remove printf these checks are unnecessary.

[yurys, 2012-04-04 12:32:16]

https://chromiumcodereview.appspot.com/9950146/diff/1/src/profile-generator.cc
File src/profile-generator.cc (right):

https://chromiumcodereview.appspot.com/9950146/diff/1/src/profile-generator.c...
src/profile-generator.cc:3511: static char* itoa(int value, char* buffer) {
On 2012/04/04 10:03:31, Mikhail Naganov (Chromium) wrote:
> Have you tried IntToCString? It uses Vector, which has overrun asserts in
debug
> mode.
IntToCString will place the number into the end of the buffer which wouldn't
work for us as we don't know number of digits beforehand. I switched this
implementation to Vector<char> so that we have overrun asserts in debug mode.

https://chromiumcodereview.appspot.com/9950146/diff/1/src/profile-generator.c...
src/profile-generator.cc:3568: STATIC_CHECK(sizeof(int) ==
sizeof(entry->type()));  // NOLINT
On 2012/04/04 11:20:49, alexeif wrote:
> If you remove printf these checks are unnecessary.
Done. Removed.

[mnaganov (inactive), 2012-04-04 12:44:31]

lgtm

[alexeif, 2012-04-04 13:01:26]

Still, what is the performance impact?

https://chromiumcodereview.appspot.com/9950146/diff/3/src/profile-generator.cc
File src/profile-generator.cc (right):

https://chromiumcodereview.appspot.com/9950146/diff/3/src/profile-generator.c...
src/profile-generator.cc:3514: value = -value;
A minor thing, but it won't work for INT_MIN. Perhaps it's worth to add a note,
so if someone decides to reuse the function he'll be aware.

[yurys, 2012-04-04 13:31:01]

On 2012/04/04 13:01:26, alexeif wrote:
> Still, what is the performance impact?
> 
See the description, it makes serialization twice as fast.

> https://chromiumcodereview.appspot.com/9950146/diff/3/src/profile-generator.cc
> File src/profile-generator.cc (right):
> 
>
https://chromiumcodereview.appspot.com/9950146/diff/3/src/profile-generator.c...
> src/profile-generator.cc:3514: value = -value;
> A minor thing, but it won't work for INT_MIN. Perhaps it's worth to add a
note,
> so if someone decides to reuse the function he'll be aware.
Done.