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Jules Villard 55586b581b [preanalysis] do not delay killing variables taken by reference ... Summary: Before, the liveness pre-analysis would place extra instructions in the CFG for either: 1. marking an `Ident.t` as dead, or 2. marking a `Pvar.t` as `= 0` But we have no way of marking pvars dead without setting them to 0. This is bad because setting pvars to 0 is not possible everywhere they are dead. Indeed, we only do it when we haven't seen their address being taken anyway. This prevents the following situation, recorded in our tests: ``` int address_taken() { int** x; int* y; int i = 7; y = &i; x = &y; // if we don't reason about taken addresses while adding nullify instructions, // we'll add // `nullify(y)` here and report a false NPE on the next line return **x; } ``` So we want to mark pvars as dead without nullifying them. This diff extends the `Remove_temps` SIL instruction to accept pvars as well, and so renames it to `ExitScope`. Reviewed By: da319 Differential Revision: D13102953 fbshipit-source-id: aa7f03a52		6 years ago
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af_test.mm	Change license to MIT	7 years ago
af_test.mm.dot	[preanalysis] do not delay killing variables taken by reference	6 years ago