context.  Test contexts are used for the left subexpressions of
short-circuited boolean operators.  The right subexpressions inherit
their expression context from the binary op expression.

Compilation of short-circuited operations in effect and test context
is straightforward:

effect(e0 || e1) =
 test(e0, L0, L1)
 L1: effect(e1)
 L0:

test(e0 || e1, L0, L1) =
 test(e0, L0, L2)
 L2: test(e1, L0, L1)

Because the value of the first subexpression may be needed as the
value of the whole expression in a value context, we introduce a
hybrid value/test contest (the value is needed if true, but not if
false).

value(e0 || e1) =
 value/test(e0, L0, L1)
 L1: value(e1)
 L0:

The compilation of value/test and test/value (introduced by boolean
AND) is:

value/test(e0 || e1, L0, L1) =
 value/test(e0, L0, L2)
 L2: value/test(e1, L0, L1)

test/value(e0 || e1, L0, L1) =
 test(e0, L0, L2)
 L2: test/value(e1, L0, L1)

Boolean AND is the dual.  The AST nodes themselves (not their parents)
are responsible for producing the proper result (effect, value, or
control flow) depending on their context.

Review URL: http://codereview.chromium.org/339082

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3187 ce2b1a6d-e550-0410-aec6-3dcde31c8c00