[AddressLowering] Handle multidefault switch_enum. #61950
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The test's correctness doesn't depend on the exact sequence of instructions. Use IDs to allow for other instructions to appear.
When rewriting uses, it is possible for new uses of a value to be created, as when a debug_value instruction is created when a store instruction is deleted. Ensure that all uses are rewritten by adding all uses to the worklist of uses after rewriting each use.
Resizing a SmallVector of SILValues fills it with invalid SILValues. THe intent is to reserve space for forthcoming values.
The filterDeadArgs function takes a list of dead argument indices--ordered from least to greatest--a list of original arguments, and produces a list of arguments excluding the arguments at those dead indices. It does that by iterating from 0 to size(originalArguments) - 1, adding the original argument at that index to the list of new arguments, so long as the index that of a dead argument. To avoid doing lookups into a set, this relies on the dead arguments being ordered ascending. There is an interator into the dead argument list that is incremented only when the current index is dead. When that iterator is at the end, dereferencing it just gives the size of the array of dead arguments. So in the case where the first argument is dead but no other arguments are, and there _are_ other arguments, the first argument would be skipped, and the second argument's index would be found to be equal to the dereferenced iterator (1). Previously, there was no check that the iterator was not at the end. The result was failing to add the second argument to the new list. And tripping an assertion failure. Here, it is checked that the iterator is not at the end.
If a switch_enum instruction (1) exhaustively handles all cases, there is no default case or block corresponding to it. If (2) it handles all cases but one, the default case corresponds to the unique unhandled case. Otherwise, (3) the default case corresponds to all the unhandled cases. The first two scenarios were already handled by address lowering. Here, handling is added for case (3). It is similar to what is already done for rewriting cases except that no unchecked_take_enum_data_addr must be created and that the argument is always address-only (being the same type as the operand of the switch_enum which is only being rewritten because it was address-only).
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If a
switch_enuminstruction (1) exhaustively handles all cases, there is no default case or block corresponding to it. If (2) it handles all cases but one, the default case corresponds to the unique unhandled case. Otherwise, (3) the default case corresponds to all the unhandled cases.The first two scenarios were already handled by address lowering.
Here, handling is added for scenario (3). It is similar to what is already done for rewriting cases except that no
unchecked_take_enum_data_addrmust be created and that the argument is always address-only (being the same type as the operand of the switch_enum which is only being rewritten because it was address-only).Based on #61945 .