Varmap2 #452
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Varmap2 #452
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I didn't look at the code, but the summary is promising! |
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Varmaps, aka environments, i.e., finite mappings from variables to their values are now represented by the Vm.t datatype. These maps are total and return a value compatible with the type of the variable. They are parametrized by an instance of the WithSubWord class telling whether said maps may hold partial values (i.e., machine words whose size is smaller than the variable they are bound to). Source-level languages enforce the “nosubword” invariant whereas lower-level languages use the relaxed “withsubword” instance. Semantics of structured languages is now parametrized by an instance of the DirectCall class. This parameter controls whether passing of function arguments and returned values behave as assignments. With the “indirect_c” instance, function arguments and returned values are truncated according to the signature of the called function. Moreover, they must not be undefined values. With the “direct_c” instance however, exchanged values are blindly copied. This more relaxed semantics enables the transformation of arrays into collections of individual variables (aka “register array expansion”) even when said arrays occur as function arguments or returned values. Indeed, even if an array is not undefined, there is no guarantee that its cells are also defined. Using the semantics with direct calls removes this constraint.
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The goal is to remove the depend map Fv.t.
This allows to generalise the semantic, in particular sem and psem can be fully unified.
Normally this should allows to extend array_expansion:
replace reg array argument and return on function call.
It should also allows to remove all the truncate stuff:
we can use sem up to regalloc, after than I think the truncate stuff are not used
anymore.