mirror of
https://github.com/golang/go
synced 2024-11-19 04:34:39 -07:00
c28bf6e069
CanonicalPos was inadequate since many pairs of instruction share the same pos (e.g. Allocs and Phis). Instead, we generalize the DebugRef instruction to associate not just Idents but Exprs with ssa.Values.
We no longer store any DebugRefs for constant expressions, to save space. (The type and value of such expressions can be obtained by other means, at a cost in complexity.)
Function.ValueForExpr queries the DebugRef info to return the ssa.Value of a given Expr.
Added tests.
Also:
- the DebugInfo flag is now per package, not global.
It must be set between Create and Build phases if desired.
- {Value,Instruction}.Pos() documentation updated: we still maintain
this information in the instruction stream even in non-debug mode,
but we make fewer claims about its invariants.
- Go and Defer instructions can now use their respective go/defer
token positions (not the call's lparen), so they do.
- SelectState:
Posn token.Pos indicates the <- position
DebugNode ast.Expr is the send stmt or receive expr.
- In building SelectStmt, we introduce extra temporaries in debug
mode to hold the result of the receive in 'case <-ch' even though
this value isn't ordinarily needed.
- Use *SelectState (indirectly) since the struct is getting bigger.
- Document some missing instructions in doc.go.
R=gri
CC=golang-dev
https://golang.org/cl/12147043
127 lines
5.8 KiB
Go
127 lines
5.8 KiB
Go
// Package ssa defines a representation of the elements of Go programs
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// (packages, types, functions, variables and constants) using a
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// static single-assignment (SSA) form intermediate representation
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// (IR) for the bodies of functions.
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//
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// THIS INTERFACE IS EXPERIMENTAL AND IS LIKELY TO CHANGE.
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//
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// For an introduction to SSA form, see
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// http://en.wikipedia.org/wiki/Static_single_assignment_form.
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// This page provides a broader reading list:
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// http://www.dcs.gla.ac.uk/~jsinger/ssa.html.
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//
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// The level of abstraction of the SSA form is intentionally close to
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// the source language to facilitate construction of source analysis
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// tools. It is not primarily intended for machine code generation.
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//
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// All looping, branching and switching constructs are replaced with
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// unstructured control flow. We may add higher-level control flow
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// primitives in the future to facilitate constant-time dispatch of
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// switch statements, for example.
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//
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// Builder encapsulates the tasks of type-checking (using go/types)
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// abstract syntax trees (as defined by go/ast) for the source files
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// comprising a Go program, and the conversion of each function from
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// Go ASTs to the SSA representation.
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//
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// By supplying an instance of the SourceLocator function prototype,
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// clients may control how the builder locates, loads and parses Go
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// sources files for imported packages. This package provides
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// MakeGoBuildLoader, which creates a loader that uses go/build to
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// locate packages in the Go source distribution, and go/parser to
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// parse them.
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//
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// The builder initially builds a naive SSA form in which all local
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// variables are addresses of stack locations with explicit loads and
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// stores. Registerisation of eligible locals and φ-node insertion
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// using dominance and dataflow are then performed as a second pass
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// called "lifting" to improve the accuracy and performance of
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// subsequent analyses; this pass can be skipped by setting the
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// NaiveForm builder flag.
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//
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// The primary interfaces of this package are:
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//
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// - Member: a named member of a Go package.
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// - Value: an expression that yields a value.
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// - Instruction: a statement that consumes values and performs computation.
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//
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// A computation that yields a result implements both the Value and
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// Instruction interfaces. The following table shows for each
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// concrete type which of these interfaces it implements.
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//
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// Value? Instruction? Member?
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// *Alloc ✔ ✔
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// *BinOp ✔ ✔
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// *Builtin ✔ ✔
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// *Call ✔ ✔
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// *Capture ✔
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// *ChangeInterface ✔ ✔
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// *ChangeType ✔ ✔
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// *Const ✔
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// *Convert ✔ ✔
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// *DebugRef ✔
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// *Defer ✔
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// *Extract ✔ ✔
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// *Field ✔ ✔
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// *FieldAddr ✔ ✔
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// *Function ✔ ✔ (func)
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// *Global ✔ ✔ (var)
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// *Go ✔
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// *If ✔
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// *Index ✔ ✔
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// *IndexAddr ✔ ✔
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// *Jump ✔
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// *Lookup ✔ ✔
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// *MakeChan ✔ ✔
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// *MakeClosure ✔ ✔
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// *MakeInterface ✔ ✔
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// *MakeMap ✔ ✔
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// *MakeSlice ✔ ✔
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// *MapUpdate ✔
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// *NamedConst ✔ (const)
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// *Next ✔ ✔
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// *Panic ✔
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// *Parameter ✔
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// *Phi ✔ ✔
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// *Range ✔ ✔
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// *Ret ✔
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// *RunDefers ✔
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// *Select ✔ ✔
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// *Send ✔
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// *Slice ✔ ✔
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// *Store ✔
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// *Type ✔ (type)
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// *TypeAssert ✔ ✔
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// *UnOp ✔ ✔
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//
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// Other key types in this package include: Program, Package, Function
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// and BasicBlock.
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//
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// The program representation constructed by this package is fully
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// resolved internally, i.e. it does not rely on the names of Values,
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// Packages, Functions, Types or BasicBlocks for the correct
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// interpretation of the program. Only the identities of objects and
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// the topology of the SSA and type graphs are semantically
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// significant. (There is one exception: Ids, used to identify field
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// and method names, contain strings.) Avoidance of name-based
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// operations simplifies the implementation of subsequent passes and
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// can make them very efficient. Many objects are nonetheless named
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// to aid in debugging, but it is not essential that the names be
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// either accurate or unambiguous. The public API exposes a number of
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// name-based maps for client convenience.
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//
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// TODO(adonovan): Consider the exceptional control-flow implications
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// of defer and recover().
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//
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// TODO(adonovan): write an example showing how to visit all functions
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// in a Program, including package init functions, methods of named
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// and anon types, and functions used as values but never called
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// directly. See AllFunctions().
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//
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// TODO(adonovan): write a how-to document for all the various cases
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// of trying to determine corresponding elements across the four
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// domains of source locations, ast.Nodes, types.Objects,
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// ssa.Values/Instructions.
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//
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package ssa
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