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Reland "[pkg/vm] Handle switch statements in unreachable code elimina…
…tor." This is a reland of commit 92bf76d In the original CL, the changes to the UCE assumed all SwitchStatements were exhaustive. Now if a SwitchStatement isn't explicitly or implicitly (via a default case) exhaustive and no case matches the tested constant, the SwitchStatement is properly removed. In addition, if a guaranteed to match case is found, more than one cases remain (thus the SwitchStatement is not removed or replaced with the single case's body), and the default case is removed, then the resulting SwitchStatement is marked as explicitly exhaustive, as this serves as a signal to backends that they do not need to handle the possibility of no case matching in the absence of a default case. Original change's description: > [pkg/vm] Handle switch statements in unreachable code eliminator. > > Namely, if the tested expression for a switch statement is constant, > then we can remove any constant cases where the constants differ, > and if all but a single case is removed, we can replace the switch > with the case body. > > If constant functions are not enabled, then getters annotated with > @pragma("vm:platform-const") are still evaluated with the constant > function evaluation machinery, but only those and no others (including > any functions called within an annotated getter). This way, functions > can be annotated with @pragma("vm:platform-const") without having to > rewrite them to be a single returned expression. > > TEST=pkg/vm/test/transformations/unreachable_code_elimination > pkg/vm/test/transformations/vm_constant_evaluator > > Issue: #50473 > Issue: #31969 > Change-Id: Ie290d2f1f469326238d66c3d9631f8e696685ff0 > Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/332760 > Commit-Queue: Tess Strickland <sstrickl@google.com> > Reviewed-by: Chloe Stefantsova <cstefantsova@google.com> > Reviewed-by: Alexander Markov <alexmarkov@google.com> TEST=pkg/vm/test/transformations/unreachable_code_elimination pkg/vm/test/transformations/vm_constant_evaluator Issue: #50473 Issue: #31969 Cq-Include-Trybots: luci.dart.try:vm-aot-linux-release-x64-try,vm-aot-mac-release-arm64-try Change-Id: I557ca933808012e670e306f2d880221a0d7dd670 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/334224 Reviewed-by: Chloe Stefantsova <cstefantsova@google.com> Reviewed-by: Alexander Markov <alexmarkov@google.com> Commit-Queue: Tess Strickland <sstrickl@google.com>
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