[SILGen] Don't assume physical lvalue components are side effect free #14410
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When emitting an ignored expression, we try not perform a load of an lvalue if we can prove that loading has no observable side effects. Previously we based this on whether the components of the lvalue are physical, however some physical components (such as force unwrapping and key-paths) have side effects. This commit introduces a new method to determine whether a component has side effects, and also adds an additional case to `emitIgnoredExpr` to avoid loading in cases where we have a force unwrap of an lvalue load (instead, if possible, try to emit the precondition using the lvalue address).
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@jckarter I'm not sure who to request a review from for this, would either yourself or someone else be available? |
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Looks good to me. |
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@swift-ci Please test |
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@jckarter Is this good to merge? |
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Yes, thanks! |
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When emitting an ignored expression (such as the argument to
type(of:)), we try not perform a load of an lvalue if we can prove that loading has no observable side effects. Previously we based this on whether the components of the lvalue are physical, however some physical components, such as force unwrapping and key-paths, have side effects (the former can trap, the latter can call arbitrary getters & setters).This PR introduces and uses a new method to determine whether a component has side effects, meaning that ignored expressions with e.g force unwrap and key-path lvalue components (see SR-1327 for examples) will have their side effects correctly evaluated.
In addition, this PR adds an additional case to
emitIgnoredExprto avoid loading in cases where we have a force unwrap of an lvalue load (instead, if possible, try to emit the precondition using the lvalue address).Resolves SR-1327.