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- At entry to each basic block, the following can be assumed (and hence
- must be forced where necessary at the end of each basic block):
- The shadow stack @stack is empty.
- For each lexical object in @pad, VALID_IV holds for each T_INT,
- VALID_DOUBLE holds for each T_DOUBLE and VALID_SV holds otherwise.
- The C shadow variable sp holds the stack pointer (not necessarily stack_sp).
- write_back_stack
- Writes the contents of the shadow stack @stack back to the real stack.
- A write-back of each object in the stack is forced so that its
- backing SV contains the right value and that SV is then pushed onto the
- real stack. On return, @stack is empty.
- write_back_lexicals
- Forces a write-back (i.e. achieves VALID_SV), where necessary, for each
- lexical object in @pad. Objects with the TEMPORARY flag are skipped. If
- write_back_lexicals is called with an (optional) argument, then it is
- taken to be a bitmask of more flags: any lexical object with one of those
- flags set is also skipped and not written back to its SV.
- invalidate_lexicals($avoid)
- The VALID_INT and VALID_DOUBLE flags are turned off for each lexical
- object in @pad whose flags field doesn't overlap with $avoid.
- reload_lexicals
- For each necessary lexical object in @pad, makes sure that VALID_IV
- holds for objects of type T_INT, VALID_DOUBLE holds for objects for
- type T_DOUBLE, and VALID_SV holds for other objects. An object is
- considered for reloading if its flags field does not overlap with the
- (optional) argument passed to reload_lexicals.
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