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diff --git a/chapter15/README.md b/chapter15/README.md index d05fca54..8ab3378b 100644 --- a/chapter15/README.md +++ b/chapter15/README.md @@ -4,6 +4,7 @@ 1. [Parser changes](#parser) 2. [TypeArray is TypeStruct](#type-array-is-typestruct) +3. [Allocation and partial memory](#allocation-and-partial-memory) 4. [New Address Math](#new-address-math) 5. [Struct Layout](#struct-layout) 6. [Some Simple Address Math Peeps](#some-simple-address-math-peeps) @@ -81,6 +82,49 @@ the Parser, users cannot write their own structs which get confused as arrays. These `TypeStruct` arrays otherwise behave exactly as a `TypeStruct`. +## Allocation and partial memory + +This chapter keeps Chapter 10b's single hidden `$mem` variable and lazy +`BulkMemPhi`/`MemPhi` partitioning. Start produces `{ctrl, $mem, arg}` and +Return consumes `{ctrl, $mem, value}`. Array initialization changes New: +instead of separate initializing Stores, New allocates and zeros the object. + +New consumes `{ctrl, $mem, size}` and produces just `{ptr, $mem}`. The pointer +is result 0 because New has no control result. Its memory input and result +cover only the field aliases in New's internal `TypeStruct`, also available +through its `TypeMemPtr`. Alias numbers are identities, not projection indices. + +For an allocation affecting aliases `A`, the parser builds: + +```text +input = MemMerge(default: absent, each a in A: before[a]) +new = New(ctrl, input, size) +ptr = Proj(new, 0) +after = MemMerge(default: before, each a in A: Proj(new, 1)) +``` + +All affected entries share the same memory projection. The input MemMerge is +partial: a null default means an unlisted alias is **not covered**. The output +aggregate retains the previous memory for unrelated aliases. An empty struct +has an empty partial input and leaves whole memory unchanged. + +Memory types now pair an alias with the type of values stored in that slice. +An alias query through New combines the incoming contents with the field's +initializer: integer zero, floating zero, or null. The query follows aggregates +and allocations, stops at cached Phi types, and records optimizer dependencies. +MemPhi merges these value types for its one alias. No per-alias New projections +or new lattice domain are needed. + +A Load using New's own pointer can fold to the initialized value. A pointer +from a distinct New can bypass the allocation to its memory input. Mere node +inequality is insufficient: a Phi or cast can still denote the allocated object. +Array length is set by a subsequent Store; the array body is zeroed by New. +Array accesses retain their existing control input as the bounds-check proxy. + +Both schedulers follow an alias through MemMerge to find New's memory effect. +MemMerge itself does not overwrite memory, but must not hide the ordering of +a read before allocation and a later write to an existing object. + ## New Address Math Since arrays need adressing math to index into them, Loads and Stores need a @@ -208,4 +252,3 @@ for( int i=0; i < ary#; i++ ) that would be entirely syntatic-sugar over the existing parser, but would really help make array looping syntax clearer. There are lots of options here, which should really be the focus of another chapter! - |