go.tools/ssa: extend debug information to arbitrary ast.Exprs.
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
diff --git a/ssa/ssa.go b/ssa/ssa.go
index c08b3e6..a0e7b91 100644
--- a/ssa/ssa.go
+++ b/ssa/ssa.go
@@ -41,6 +41,7 @@
Members map[string]Member // all package members keyed by name
values map[types.Object]Value // package-level vars & funcs (incl. methods), keyed by object
init *Function // Func("init"); the package's (concatenated) init function
+ debug bool // include full debug info in this package.
// The following fields are set transiently, then cleared
// after building.
@@ -125,14 +126,20 @@
// Instruction.Operands contains the inverse of this relation.
Referrers() *[]Instruction
- // Pos returns the location of the source construct that
- // gave rise to this value, or token.NoPos if it was not
- // explicit in the source.
+ // Pos returns the location of the AST token most closely
+ // associated with the operation that gave rise to this value,
+ // or token.NoPos if it was not explicit in the source.
//
- // For each ast.Expr type, a particular field is designated as
- // the canonical location for the expression, e.g. the Lparen
- // for an *ast.CallExpr. This enables us to find the value
- // corresponding to a given piece of source syntax.
+ // For each ast.Node type, a particular token is designated as
+ // the closest location for the expression, e.g. the Lparen
+ // for an *ast.CallExpr. This permits a compact but
+ // approximate mapping from Values to source positions for use
+ // in diagnostic messages, for example.
+ //
+ // (Do not use this position to determine which Value
+ // corresponds to an ast.Expr; use Function.ValueForExpr
+ // instead. NB: it requires that the function was built with
+ // debug information.)
//
Pos() token.Pos
}
@@ -191,15 +198,22 @@
// Values.)
Operands(rands []*Value) []*Value
- // Pos returns the location of the source construct that
- // gave rise to this instruction, or token.NoPos if it was not
- // explicit in the source.
+ // Pos returns the location of the AST token most closely
+ // associated with the operation that gave rise to this
+ // instruction, or token.NoPos if it was not explicit in the
+ // source.
//
- // For each ast.Expr type, a particular field is designated as
- // the canonical location for the expression, e.g. the Lparen
- // for an *ast.CallExpr. This enables us to find the
- // instruction corresponding to a given piece of source
- // syntax.
+ // For each ast.Node type, a particular token is designated as
+ // the closest location for the expression, e.g. the Go token
+ // for an *ast.GoStmt. This permits a compact but approximate
+ // mapping from Instructions to source positions for use in
+ // diagnostic messages, for example.
+ //
+ // (Do not use this position to determine which Instruction
+ // corresponds to an ast.Expr; see the notes for Value.Pos.
+ // This position may be used to determine which non-Value
+ // Instruction corresponds to some ast.Stmts, but not all: If
+ // and Jump instructions have no Pos(), for example.)
//
Pos() token.Pos
}
@@ -791,10 +805,11 @@
// It represents one goal state and its corresponding communication.
//
type SelectState struct {
- Dir ast.ChanDir // direction of case
- Chan Value // channel to use (for send or receive)
- Send Value // value to send (for send)
- Pos token.Pos // position of token.ARROW
+ Dir ast.ChanDir // direction of case
+ Chan Value // channel to use (for send or receive)
+ Send Value // value to send (for send)
+ Pos token.Pos // position of token.ARROW
+ DebugNode ast.Node // ast.SendStmt or ast.UnaryExpr(<-) [debug mode]
}
// The Select instruction tests whether (or blocks until) one or more
@@ -834,7 +849,7 @@
//
type Select struct {
Register
- States []SelectState
+ States []*SelectState
Blocking bool
}
@@ -906,8 +921,9 @@
//
// Pos() returns the ast.CallExpr.Lparen if the instruction arose from
// an explicit T(e) conversion; the ast.TypeAssertExpr.Lparen if the
-// instruction arose from an explicit e.(T) operation; or token.NoPos
-// otherwise.
+// instruction arose from an explicit e.(T) operation; or the
+// ast.CaseClause.Case if the instruction arose from a case of a
+// type-switch statement.
//
// Example printed form:
// t1 = typeassert t0.(int)
@@ -1037,6 +1053,8 @@
//
// See CallCommon for generic function call documentation.
//
+// Pos() returns the ast.GoStmt.Go.
+//
// Example printed form:
// go println(t0, t1)
// go t3()
@@ -1045,6 +1063,7 @@
type Go struct {
anInstruction
Call CallCommon
+ pos token.Pos
}
// The Defer instruction pushes the specified call onto a stack of
@@ -1052,6 +1071,8 @@
//
// See CallCommon for generic function call documentation.
//
+// Pos() returns the ast.DeferStmt.Defer.
+//
// Example printed form:
// defer println(t0, t1)
// defer t3()
@@ -1060,6 +1081,7 @@
type Defer struct {
anInstruction
Call CallCommon
+ pos token.Pos
}
// The Send instruction sends X on channel Chan.
@@ -1107,15 +1129,15 @@
}
// A DebugRef instruction provides the position information for a
-// specific source-level reference that denotes the SSA value X.
+// specific source-level expression that compiles to the SSA value X.
//
// DebugRef is a pseudo-instruction: it has no dynamic effect.
//
-// Pos() returns the ast.Ident or ast.Selector.Sel of the source-level
-// reference.
+// Pos() returns Expr.Pos(), the position of the source-level
+// expression.
//
-// Object() returns the source-level (var/const) object denoted by
-// that reference.
+// Object() returns the source-level (var/const/func) object denoted
+// by Expr if it is an *ast.Ident; otherwise it is nil.
//
// (By representing these as instructions, rather than out-of-band,
// consistency is maintained during transformation passes by the
@@ -1124,8 +1146,8 @@
type DebugRef struct {
anInstruction
X Value // the value whose position we're declaring
- pos token.Pos // location of the reference
- object types.Object // the identity of the source var/const
+ Expr ast.Expr // the referring expression
+ object types.Object // the identity of the source var/const/func
}
// Embeddable mix-ins and helpers for common parts of other structs. -----------
@@ -1385,8 +1407,8 @@
}
func (v *Call) Pos() token.Pos { return v.Call.pos }
-func (s *Defer) Pos() token.Pos { return s.Call.pos }
-func (s *Go) Pos() token.Pos { return s.Call.pos }
+func (s *Defer) Pos() token.Pos { return s.pos }
+func (s *Go) Pos() token.Pos { return s.pos }
func (s *MapUpdate) Pos() token.Pos { return s.pos }
func (s *Panic) Pos() token.Pos { return s.pos }
func (s *Ret) Pos() token.Pos { return s.pos }
@@ -1395,7 +1417,7 @@
func (s *If) Pos() token.Pos { return token.NoPos }
func (s *Jump) Pos() token.Pos { return token.NoPos }
func (s *RunDefers) Pos() token.Pos { return token.NoPos }
-func (s *DebugRef) Pos() token.Pos { return s.pos }
+func (s *DebugRef) Pos() token.Pos { return s.Expr.Pos() }
// Operands.
