[wasm] Remember import indices with the compiled module

[wasm] Remember import indices

When compiling a wasm module, we initially generate placeholders for
imports, which store the index corresponding to that import. Later,
at instantiation time, we use that index to correctly link the
provided import.

In this scheme, supporting multiple instantiations requires we
preserve a template (set of unlinked compiled wasm functions) which
we clone for each instance. To avoid holding on to this template,
which may be large (wasm compiled code should be expected to be in
the order of tens of MB), we must enable cloning from an instance's
linked wasm functions.

This change is a step in that direction. Instead of assuming the wasm
functions reference placeholders, we store a table of the code objects
used for imports together with the compiled module, and use that
information to determine the index of the import. Initially, that
table contains placeholders. For instances, however, that table contains
their actual imports.

BUG=

Committed: https://crrev.com/5524cbf5b8324051da7145ef3c8b7e80b2e7ab28
Cr-Commit-Position: refs/heads/master@{#38848}

[Mircea Trofin, 2016-08-23 22:38:06]

The CQ bit was checked by mtrofin@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-08-23 22:38:15]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-23 22:42:49]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-08-23 22:42:50]

Dry run: Try jobs failed on following builders:
  v8_win_nosnap_shared_rel_ng on master.tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_win_nosnap_shared_rel_ng...)

[Mircea Trofin, 2016-08-23 23:21:37]

The CQ bit was checked by mtrofin@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-08-23 23:21:44]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Mircea Trofin, 2016-08-23 23:34:54]

mtrofin@chromium.org changed reviewers:
+ bradnelson@chromium.org

[Mircea Trofin, 2016-08-23 23:34:54]

ptal

[commit-bot: I haz the power, 2016-08-23 23:50:28]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-08-23 23:50:29]

Dry run: This issue passed the CQ dry run.

[bradnelson, 2016-08-24 00:23:35]

The CQ bit was checked by bradnelson@chromium.org

[bradnelson, 2016-08-24 00:23:36]

lgtm

[commit-bot: I haz the power, 2016-08-24 00:23:41]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-24 00:26:01]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-08-24 00:26:24]

Description was changed from

==========
[wasm] Remember import indices

When compiling a wasm module, we initially generate placeholders for
imports, which store the index corresponding to that import. Later,
at instantiation time, we use that index to correctly link the
provided import.

In this scheme, supporting multiple instantiations requires we
preserve a template (set of unlinked compiled wasm functions) which
we clone for each instance. To avoid holding on to this template,
which may be large (wasm compiled code should be expected to be in
the order of tens of MB), we must enable cloning from an instance's
linked wasm functions.

This change is a step in that direction. Instead of assuming the wasm
functions reference placeholders, we store a table of the code objects
used for imports together with the compiled module, and use that
information to determine the index of the import. Initially, that
table contains placeholders. For instances, however, that table contains
their actual imports.

BUG=
==========

to

==========
[wasm] Remember import indices

When compiling a wasm module, we initially generate placeholders for
imports, which store the index corresponding to that import. Later,
at instantiation time, we use that index to correctly link the
provided import.

In this scheme, supporting multiple instantiations requires we
preserve a template (set of unlinked compiled wasm functions) which
we clone for each instance. To avoid holding on to this template,
which may be large (wasm compiled code should be expected to be in
the order of tens of MB), we must enable cloning from an instance's
linked wasm functions.

This change is a step in that direction. Instead of assuming the wasm
functions reference placeholders, we store a table of the code objects
used for imports together with the compiled module, and use that
information to determine the index of the import. Initially, that
table contains placeholders. For instances, however, that table contains
their actual imports.

BUG=

Committed: https://crrev.com/5524cbf5b8324051da7145ef3c8b7e80b2e7ab28
Cr-Commit-Position: refs/heads/master@{#38848}
==========

[commit-bot: I haz the power, 2016-08-24 00:26:25]

Patchset 2 (id:??) landed as
https://crrev.com/5524cbf5b8324051da7145ef3c8b7e80b2e7ab28
Cr-Commit-Position: refs/heads/master@{#38848}