[os_log][SIL Optimization] Make new os log APIs @_transparent and change OSLogOptimization pass so that inlining is not performed.

[ravikandhadai]

@atrick @eeckstein, I have made a change to the OSLogOptimization pass to address an issue raised by @gottesmm. Basically, I have removed inlining from the pass, which caused problems as the pass was in the mandatory pipeline but wasn't using Mandatory inlining (which happens earlier). The reason for that was that the pass used @_semantics attribute to identify log calls, extract the custom string interpolation argument of the call, and identify the instructions that must be constant evaluated. The call and the @_semantics attribute will be lost by mandatory inlining.

This commit changes how the instructions to constant evaluate are identified. The new approach uses the "initializer" calls of the custom string interpolation type: 'OSLogMessage' to drive the constant evaluation and folding. The initializer calls need not be inlined and are constant evaluable. The main benefit of the current approach is that, it will kick in at every place where the type 'OSLogMessage' is instantiated using a string interpolation, regardless of whether or not it is passed to a os_log call. E.g. the optimization will also apply to cases like the following.

    let x: OSLogMessage = "Hello \(1)"
    let y = x.formatString // This will be constant folded. 

A note: the diagnostics in this pass will be subsumed and enhanced by a new pass that will enforce the library implementation model (by checking if the implementation is constant evaluable etc.) and also the user model for the log calls (by checking if the log calls are passed a string interpolation). The diagnostics in this pass will eventually become redundant and should just be asserts/noops.

[ravikandhadai]

@swift-ci Please test

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[gottesmm]

So to be clear: you marked the initializer with a semantic call so you could just constant fold it instead of inlining it?

[gottesmm]

1. For this to work when ownership is enabled, you need to at least handle destroy_value and probably need to look through copy_value.
2. Is this a struct or a class? If it is a class, you probably also need strong_release.

[ravikandhadai]

So to be clear: you marked the initializer with a semantic call so you could just constant fold it instead of inlining it?

Yes, that's right. One thing I would add is that the initializer was always constant evaluated but was mandatorily inlined earlier and then evaluated. Now it is marked with @_semantics and not mandatorily inlined (it can still be constant evaluated), and more importantly it is used to identify the range of instructions to evaluate.

[ravikandhadai]

• For this to work when ownership is enabled, you need to at least handle destroy_value and probably need to look through copy_value.
• Is this a struct or a class? If it is a class, you probably also need strong_release.

This is a struct. I see. Thanks for the update, I will watch out for that. Actually, this condition is more of a safe guard and in reality the evaluation should break even before this instruction as there will instructions that it cannot constant evaluate (due to the implementation of os_log) and will bail out earlier.

[ravikandhadai]

@swift-ci Please test linux platform

[gottesmm]

Can you add the destroy-value and copy value plz

[ravikandhadai]

Can you add the destroy-value and copy value plz

Okay. Will copy_value happen just before destroy_value? In that case, it and also destroy_value can be used as a break condition

[ravikandhadai]

I pushed a commit that makes the OSLogOptimization pass work on ownership SIL. The following are the two main changes:

• Fold results of instructions like destructure_tuple that could return multiple results and some of which are foldable.
• Include destroy_value and copy_value in end of lifetime checks that is used to stop evaluation.

There is still a problem in this pass that causes ownership verification to fail. (Basically, the string initialization instructions that are created to fold string literals are not released.) Excepting this, the pass works on ownership SIL (i.e., when ownership stripping happens after serialization). I will a create follow up PR to address this problem, and also create PRs for changes to the constant evaluator to handle ownership SIL instructions.

[ravikandhadai]

@swift-ci Please test

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[gottesmm]

@ravikandhadai was the lack of releasing of the initialization instructions a /real/ bug?

[gottesmm]

Also, you may want to look at destructure_struct as well.

[ravikandhadai]

@ravikandhadai was the lack of releasing of the initialization instructions a /real/ bug?

Yes, it was a leak, but only discovered by the ownership verifier. Basically, when an instruction like %str = struct_extract S.str is folded and replaced by a string constant, the optimizer should also add a release/destroy _value instruction. I have updated the code so that cases like these are handled. Now the optimization pass also works with ownership SIL (but for rdar://51512044).

The main changes for this is in the function destroyFoldedValueAtEndOfUse which is called by substituteConstants.

[ravikandhadai]

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[ravikandhadai]

@swift-ci Please test macOS Platform

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[ravikandhadai]

@swift-ci Please smoke test macOS Platform

[ravikandhadai]

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[ravikandhadai]

@swift-ci Please test macOS Platform

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[ravikandhadai]

@swift-ci Please clean test macOS Platform