SSA2 is an IntermediateLanguage, translated from SSA by ToSSA2, optimized by SSA2Simplify, and translated by ToRSSA to RSSA.
Description
SSA2 is a FirstOrder, SimplyTyped IntermediateLanguage, a slight variant of the SSA IntermediateLanguage,
Like SSA, an SSA2 program consists of a collection of datatype declarations, a sequence of global statements, and a collection of functions, along with a distinguished "main" function. Each function consists of a collection of basic blocks, where each basic block is a sequence of statements ending with some control transfer.
Unlike SSA, SSA2 includes mutable fields in objects and makes the vector type constructor n-ary instead of unary. This allows optimizations like RefFlatten and DeepFlatten to be expressed.
Implementation
Type Checking
Type checking (type-check2.sig, type-check2.fun) of a SSA2 program verifies the following:
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no duplicate definitions (tycons, cons, vars, labels, funcs)
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no out of scope references (tycons, cons, vars, labels, funcs)
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variable definitions dominate variable uses
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case transfers are exhaustive and irredundant
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Enter/Leave profile statements match
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"traditional" well-typedness
Details and Notes
SSA is an abbreviation for Static Single Assignment.