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The stringview types from the stringref proposal have three irregularities that
break common invariants and require pervasive special casing to handle properly:
they are supertypes of `none` but not subtypes of `any`, they cannot be the
targets of casts, and they cannot be used to construct nullable references. At
the same time, the stringref proposal has been superseded by the imported
strings proposal, which does not have these irregularities. The cost of
maintaing and improving our support for stringview types is no longer worth the
benefit of supporting them.
Simplify the code base by entirely removing the stringview types and related
instructions that do not have analogues in the imported strings proposal and do
not make sense in the absense of stringviews.
Three remaining instructions, `stringview_wtf16.get_codeunit`,
`stringview_wtf16.slice`, and `stringview_wtf16.length` take stringview operands
in the stringref proposal but cannot be removed because they lower to operations
from the imported strings proposal. These instructions are changed to take
stringref operands in Binaryen IR, and to allow a graceful upgrade path for
users of these instructions, the text and binary parsers still accept but ignore
`string.as_wtf16`, which is the instruction used to convert stringrefs to
stringviews. The binary writer emits code sequences that use scratch locals and `string.as_wtf16` to keep the output valid.
Future PRs will further align binaryen with the imported strings proposal
instead of the stringref proposal, for example by making `string` a subtype of
`extern` instead of a subtype of `any` and by removing additional instructions
that do not have analogues in the imported strings proposal.
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intialization (#6571)
Constants that need to be hoisted sometimes are initialized by calling
getters of other constants that need to be hoisted. These getters are
non-trivial, e.g.
(func $getConst1_<once>_@X (result (ref null $A))
(block (result (ref null $A))
(if (i32.eqz (ref.is_null (global.get $$const1@X)))
(then
(return (global.get $$const1@X))
)
)
(global.set $$const1@X (struct.new $A (i32.const 2)))
(global.get $$const1@X)
)
(func $getConst2_<once>_@X (result (ref null $A))
(block (result (ref null $A))
(if (i32.eqz (ref.is_null (global.get $$const2@X)))
(then
(return (global.get $$const2@X))
)
)
(global.set $$const2@X .... expression with (call $getConst1_<once>_@X) ....))
(global.get $$const2@X)
)
and can only be simplified after the constants they initialize are hoisted. After
the constant is hoisted the getter can be inlined and constants that depend on
it for their initialization can now be hoisted.
Before this pass, inlining would happen after the pass was run by a subsequent
run of the inliner (likely as part of -O3), requiring as many runs of this pass,
interleaved with the inliner, as the depth in the call sequence.
By having a simpler inliner run as part of the loop in this pass, the pass becomes
more effective and more independent of the call depths.
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We previously supported (and primarily used) a non-standard text format for
conditionals in which the condition, if-true expression, and if-false expression
were all simply s-expression children of the `if` expression. The standard text
format, however, requires the use of `then` and `else` forms to introduce the
if-true and if-false arms of the conditional. Update the legacy text parser to
require the standard format and update all tests to match. Update the printer to
print the standard format as well.
The .wast and .wat test inputs were mechanically updated with this script:
https://gist.github.com/tlively/85ae7f01f92f772241ec994c840ccbb1
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Existing convention uses _@once@_ but we also use @ for class separation.
It is cleaner&more future proof to use something other convention like _<once>_.
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The patch puts a new guardrail that will only hoist the field
if it is initialized with the owner class.
The constant hoisting optimization in J2CL pass relies on the
assumption that clinit that will initialize the field will be
executed before the read of the field. That means the field
that is optimized is within the same class:
class Foo {
public static final Object field = new Object();
}
Although it is possible to observe the initial value, that is
not intention of the developer (which the point of the
optimization).
However can also see a similar pattern in following:
class Foo {
public static Object field;
}
class Zoo {
static {
Foo.field = new Object();
}
}
Currently the pass also optimizes it as well since the field
is only initialized once and by a clinit. However Zoo clinit
is not guaranteed to be run before Foo.field access so it is
less safe to speculate on the intention of the developer here
hence it is not worth the risk.
FWIW, we haven't seen this issue. But this is something we
are also guarding in Closure Compiler so I decided it is
worthwhile to do here as well.
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This PR creates a new pass to optimize J2CL specific patterns
that would otherwise difficult to recognize/prove generically
by other binaryen passes.
The pass currently handles fields what we call as "constant-like".
These fields are fields initialized once and unconditionally through
"clinit" function and technically they do have 2 observable states;
- initial null/0 state
- initialized state.
However you can only observe initial null/0 state in contrived examples,
not in real world/correct applications.
This pass moves such "clinit" initialized fields to global initialization.
Above pattern also matches other lazy init construct like String and Class
literals (which binaryen already reduces to constant expressions). So
the pass is generalized to include them as well. (by matching any functions
with the name pattern "_@once_")
In order for this pass to be effective:
1. It needs to run between O3 passes
2. We need to stop inlining of "once" functions.
Stopping inlining of the once functions are important to preserve their
structure. This both helps existing OnceReducer pass and new J2CL pass to
be a lot more effective. Also it is not useful to inline these functions
as by defintion they only executed once. This could be achieved by passing
no-inline filter.
Although the inlining is generally disabled for these functions, it is
still needed for some cases since inliner is effectively responsible for
removal of the once functions that are simplified into empty or simple
delegating functions. For this reason, the pass will rename such trivial
function so no-inline filter will no longer match them.
Also note that after all optimizations completed, it does make sense to
have a final stage where the "partial inline" of all once functions are
allowed. This will speed them up by moving the initialization check to
call-site.
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