Fix issues with the conditional discard workarounds to do with assignments.

Fix issues with the conditional discard workarounds to do with assignments.

The old modifiesState method really checked if an operator was an assignment,
so restored that behaviour and use the new side effects detection only for
the new code.

ANGLEBUG=486
BUG=
R=nicolascapens@chromium.org, zmo@chromium.org

Committed: https://code.google.com/p/angleproject/source/detail?r=a60e080

[Jamie Madill, 2013-11-05 21:08:32]

Please take a look!

[zmo, 2013-11-05 22:00:47]

On 2013/11/05 21:08:32, Jamie Madill wrote:
> Please take a look!

Looks fine to me, but I'll let nicolas decide.

[nicolascapens, 2013-11-06 22:48:36]

LGTM

https://codereview.appspot.com/22130043/diff/1/src/compiler/Intermediate.cpp
File src/compiler/Intermediate.cpp (right):

https://codereview.appspot.com/22130043/diff/1/src/compiler/Intermediate.cpp#...
src/compiler/Intermediate.cpp:815: case EOpPreDecrement:
Increment/decrement are strictly speaking not assignments but just like an
assignment they store a new value in a variable, so it's probably not too
confusing. But perhaps the comment can clarify that the operator assigns a new
value instead of being an assignment (which is kind of redundant given the
method name).

Actually, that's what the first line of the comment says, so the second line can
simply be removed.

[Jamie Madill, 2013-11-07 16:03:49]

Committed patchset #1 manually as ra60e080 (presubmit successful).