A function such as this:
func one() (x int) {
defer func() { recover() }()
x = 1
panic("return")
}
that combines named return parameters (NRPs) with deferred calls
that call recover, may return non-zero values despite the
fact it doesn't even contain a return statement. (!)
This requires a change to the SSA API: all functions'
control-flow graphs now have a second entry point, called
Recover, which is the block at which control flow resumes
after a recovered panic. The Recover block simply loads the
NRPs and returns them.
As an optimization, most functions don't need a Recover block,
so it is omitted. In fact it is only needed for functions that
have NRPs and defer a call to another function that _may_ call
recover.
Dataflow analysis of SSA now requires extra work, since every
may-panic instruction has an implicit control-flow edge to
the Recover block. The only dataflow analysis so far implemented
is SSA renaming, for which we make the following simplifying
assumption: the Recover block only loads the NRPs and returns.
This means we don't really need to analyze it, we can just
skip the "lifting" of such NRPs. We also special-case the Recover
block in the dominance computation.
Rejected alternative approaches:
- Specifying a Recover block for every defer instruction (like a
traditional exception handler).
This seemed like excessive generality, since Go programs
only need the same degenerate form of Recover block.
- Adding an instruction to set the Recover block immediately
after the named return values are set up, so that dominance
can be computed without special-casing.
This didn't seem worth the effort.
Interpreter:
- This CL completely reimplements the panic/recover/
defer logic in the interpreter. It's clearer and simpler
and closer to the model in the spec.
- Some runtime panic messages have been changed to be closer
to gc's, since tests depend on it.
- The interpreter now requires that the runtime.runtimeError
type be part of the SSA program. This requires that clients
import this package prior to invoking the interpreter.
This in turn requires (Importer).ImportPackage(path string),
which this CL adds.
- All $GOROOT/test/recover{,1,2,3}.go tests are now passing.
NB, the bug described in coverage.go (defer/recover in a concatenated
init function) remains. Will be fixed in a follow-up.
Fixesgolang/go#6381
R=gri
CC=crawshaw, golang-dev
https://golang.org/cl/13844043
(Motivation: "Literal" is a syntactic property, not a semantic one.)
Also: delete a "TODO: opt" that the lifting pass already does for us.
R=gri
CC=golang-dev
https://golang.org/cl/11351043
Objects:
- provide IsExported, SameName, uniqueName methods
- clean up a lot of dependent code
Scopes:
- don't add children to Universe scope (!)
- document Node, WriteTo
Types:
- remove Deref in favor of internal function deref
ssa, ssa/interp:
- introduced local deref, adjusted code
- fixed some "Underlying" bugs (pun intended)
R=adonovan
CC=golang-dev
https://golang.org/cl/11232043
Method sets:
- Simplify CallCommon.
Avoid the implicit copy when calling a T method on a *T
receiver. This simplifies clients. Instead we generate
"indirection wrapper" functions that do this (like gc does).
New invariant:
m's receiver type is exactly T for all m in MethodSet(T)
- MakeInterface no longer holds the concrete type's MethodSet.
We can defer its computation this way.
- ssa.Type now just wraps a types.TypeName object.
MethodSets are computed as needed, not eagerly.
Position info:
- new CanonicalPos utility maps ast.Expr to canonical
token.Pos, as returned by {Instruction,Value}.Pos() methods.
- Don't set posn for implicit operations (e.g. varargs array alloc)
- Set position info for ChangeInterface and Slice instructions.
Cosmetic:
- add Member.Token() method
- simplify isPointer
- Omit words "interface", "slice" when printing MakeInterface,
MakeSlice; the type is enough.
- Comments on PathEnclosingInterval.
- Remove Function.FullName() where implicit String() suffices.
Also:
- Exposed NewLiteral to clients.
- Added ssa.Instruction.Parent() *Function
Added ssa.BasicBlock.Parent() *Function.
Added Sanity checks for above.
R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/10166045
Implement Pos() method for
Values: Parameter, Capture, Phi. (Not Literal, Builtin.)
Instructions: UnOp, BinOp, Store.
'address' (an lvalue) now needs position of '*' in "*addr".
Also:
- Un-export fields Pos_ Type_ Name_ Block_ from various values/instructions.
Define NewFunction() as a temporary measure.
Will try to eliminate calls from clients...
- Remove Implements{Value,Member,Interface} marker methods.
I've decided I don't like them.
- Func.addParamObj helper.
- Various comment fixes.
R=gri
CC=golang-dev
https://golang.org/cl/9740046
Alan Donovan
Robert Griesemer
Rob Pike