Overview: Function.finish() now invokes the "lifting" pass which replaces local allocs and loads and stores to such cells by SSA registers.  We use very standard machinery:

(1) we build the dominator tree for the function's control flow graph (CFG) using the "Simple" Lengauer-Tarjan algorithm.  (Very "simple" in fact: even simple path compression is not yet implemented.)

In sanity-checking mode, we cross check the dominator tree against an alternative implementation using a simple iterative dataflow algorithm.
This all lives in dom.go, along with some diagnostic printing routines.

(2) we build the dominance frontier for the entire CFG using the Cytron et al algorithm.  The DF is represented as a slice of slices, keyed by block index.  See buildDomFrontier() in lift.go.

(3) we determine for each Alloc whether it can be lifted: is it only subject to loads and stores?  If so, we traverse the iterated dominance frontier (IDF) creating φ-nodes; they are not prepended to the blocks yet.
See liftAlloc() in lift.go.

(4) we perform the SSA renaming algorithm from Cytron et al, replacing all loads to lifted Alloc cells by the value stored by the dominating store operation, and deleting the stores and allocs.  See rename() in lift.go.

(5) we eliminate unneeded φ-nodes, then concatenate the remaining ones with the non-deleted instructions of the block into a new slice.  We eliminate any lifted allocs from Function.Locals.

To ease reviewing, I have avoided almost all optimisations at this point, though there are many opportunities to explore.  These will be easier to understand as follow-up changes.

All the existing tests (pending CL 7313062) pass.  (Faster!)

Details:

"NaiveForm" BuilderMode flag suppresses all the new logic.
Exposed as 'ssadump -build=N'.

BasicBlock:
- add .Index field (b.Func[b.Index]==b), simplifying
  algorithms such as Kildall-style dataflow with bitvectors.
- rename the Name field to Comment to better reflect its
  reduced purpose.  It now has a String() method.
- 'dom' field holds dominator tree node; private for now.
- new predIndex method.
- hasPhi is now a method

dom.go:
- domTree: a new struct for a node in a dominator tree.
- buildDomTree builds the dominator tree using the simple
  variant Lengauer/Tarjan algorithm with Georgiadis'
  bucket optimizations.
- sanityCheckDomTree builds dominance relation using
  Kildall-style dataflow and ensures the same result is
  obtained.
- printDomTreeDot prints the CFG/DomTree in GraphViz format.

blockopt.go:
- perform a mark/sweep pass to eliminate unreachable
  cycles; the previous prune() opt would only eliminate
  trivially dead blocks.  (Needed for LT algo.)
- using .Index, fuseblocks can now delete fused blocks directly.
- delete prune().

sanity.go: more consistency checks:
- Phi with missing edge value
- local Alloc instructions must appear in Function.Locals.
- BasicBlock.Index, Func consistency
- CFG edges are all intraprocedural.
- detect nils in BasicBlock.Instrs.
- detect Function.Locals with Heap flag set.
- check fn.Blocks is nil if empty.

Also:
- Phi now has Comment field for debugging.
- Fixed bug in Select.Operands()
  (took address of temporary copy of field)
- new Literal constructor zeroLiteral().
- algorithms steal private fields Alloc.index,
  BasicBlock.gaps to avoid allocating maps.
- We print Function.Locals in DumpTo.
- added profiling support to ssadump.

R=iant, gri
CC=golang-dev
https://golang.org/cl/7229074

mpreinit() is called on the parent thread and with mcache (can allocate memory),
minit() is called on the child thread and can not allocate memory.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7389043

And add a test too, for Alex. :)

Fixes #3734

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/7399046

* allow commit watcher to be disabled, useful for small slow builders who will never be the first to notice a commit.
* builders always update their local master working copy before cloning a specific revision.
* refactor hg repo operations into a new type, Repo.

R=adg, shanemhansen, luitvd
CC=golang-dev
https://golang.org/cl/7326053

Minor simplification of gcimporter, removed TODO.

R=adonovan
CC=golang-dev
https://golang.org/cl/7363044

Fixes #4852

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/7374045

R=nigeltao
CC=golang-dev
https://golang.org/cl/7399044

Simplifies the contract for Driver.Stmt.Close in
the process of fixing issue 3865.

Fixes #3865
Update #4459 (maybe fixes it; uninvestigated)

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7363043

Fixes #4435.

R=golang-dev, iant, alex.brainman, minux.ma, dvyukov
CC=golang-dev
https://golang.org/cl/7304104

Mimic the Emacs convention of presenting read-only files meant
for browsing using view-mode, rather than Fundamental mode
which mistakenly allows editing of the "godoc" content.
Fixes #4322.

R=golang-dev, bradfitz, sameer
CC=golang-dev
https://golang.org/cl/7231055

Generated by addca.

R=gobot
CC=golang-dev
https://golang.org/cl/7377045

Fixes #4112.

R=remyoudompheng, daniel.morsing, dave, rsc
CC=golang-dev
https://golang.org/cl/7085053

Generated by addca.

R=gobot
CC=golang-dev
https://golang.org/cl/7400045

Also close the file when we're done.

R=bradfitz
CC=golang-dev
https://golang.org/cl/7363045

Apply width when using Printf with nil values.
Fixes #4772.

R=r, adg
CC=golang-dev
https://golang.org/cl/7314114

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7386045

R=rsc
CC=golang-dev
https://golang.org/cl/7385045

R=rsc
CC=golang-dev
https://golang.org/cl/7381046

(per r's suggestion)

R=r
CC=golang-dev
https://golang.org/cl/7376045

Add a new, simple interface for scanning (probably textual) data,
based on a new type called Scanner. It does its own internal buffering,
so should be plausibly efficient even without injecting a bufio.Reader.
The format of the input is defined by a "split function", by default
splitting into lines. Other implemented split functions include single
bytes, single runes, and space-separated words.

Here's the loop to scan stdin as a file of lines:

        s := bufio.NewScanner(os.Stdin)
        for s.Scan() {
                fmt.Printf("%s\n", s.Bytes())
        }
        if s.Err() != nil {
                log.Fatal(s.Err())
        }

While we're dealing with spaces, define what space means to strings.Fields.

Fixes #4802.

R=adg, rogpeppe, bradfitz, rsc
CC=golang-dev
https://golang.org/cl/7322088

(Offsetof is a function of Alignof and Sizeof.)

- removed IntSize, PtrSize from Context (set Sizeof instead)
- GcImporter needs a Context now (it needs to have
  access to Sizeof/Alignof)
- removed exported Size field from Basic (use Sizeof)
- added Offset to Field
- added Alignment, Size to Struct

R=adonovan
CC=golang-dev
https://golang.org/cl/7357046

Can not happen ATM. In preparation for the new scheduler.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7388043

In preparation for the new scheduler.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7386044

This is followup to https://golang.org/cl/7319050/

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/7379043

Fixes #4819.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/7322086

The removed code leads to the situation when M executes the same locked G again
and again.
This is https://golang.org/cl/7310096 but with return instead of break
in the nested switch.
Fixes #4820.

R=golang-dev, alex.brainman, rsc
CC=golang-dev
https://golang.org/cl/7304102

The Camlistore code tree rearranged after the go tool came
out. (I didn't know this link was here until I saw it in
some logs.)

R=adg
CC=golang-dev
https://golang.org/cl/7374043

On Windows, directory names in PATH can be fully or partially quoted
in double quotes ('"'), but the path names as used by most APIs must
be unquoted. In addition, quoted names can contain the semicolon
(';') character, which is otherwise used as ListSeparator.

This CL changes SplitList in path/filepath and LookPath in os/exec
to only	treat unquoted semicolons as separators, and to unquote the
separated elements.

(In addition, fix harmless test bug I introduced for LookPath on Unix.)

Related discussion thread:
https://groups.google.com/d/msg/golang-nuts/PXCr10DsRb4/sawZBM7scYgJ

R=rsc, minux.ma, mccoyst, alex.brainman, iant
CC=golang-dev
https://golang.org/cl/7181047

Fixes #4844.

R=golang-dev, alex.brainman
CC=golang-dev
https://golang.org/cl/7366043

R=r, golang-dev
CC=golang-dev
https://golang.org/cl/7327053

The data file should be opened when a Conn is first
established, rather than waiting for the first Read or
Write.

Upon Close, we now make sure to try to close both, the
ctl as well as data files and set both to nil, even in
the face of errors, instead of returning early.

The Accept call was not setting the remote address
of the connection properly. Now, we read the correct
file.

Make functions that establish Conn use newTCPConn
or newUDPConn.

R=rsc, rminnich, ality, dave
CC=golang-dev
https://golang.org/cl/7228068

This CL changes nothing to existing API behavior, just sets up
Zone in IPNet and IPAddr structures if possible.

Also does small simplification.

Update #4234.

R=rsc, dave
CC=golang-dev
https://golang.org/cl/7300081

On Linux point-to-point interface an IFA_ADDRESS attribute
represents a peer address. For a correct interface address
we should take an IFA_LOCAL attribute instead.

Fixes #4839.

R=golang-dev, dave, rsc
CC=golang-dev
https://golang.org/cl/7352045

This avoids ambiguity and makes the diagnostics closer to
those issued by gc, but it is more verbose since it qualifies
intra-package references.

Without extra context---e.g. a 'from *Package' parameter to
Type.String()---we are forced to err on one side or the other.

Also, cosmetic changes to exp/ssa:
- Remove package-qualification workaround in Function.FullName.
- Always set go/types.Package.Path field to the import path,
  since we know the correct path at this point.
- In Function.DumpTo, show variadic '...' and result type info,
  and delete now-redundant "# Type: " line.

R=gri
CC=golang-dev
https://golang.org/cl/7325051

R=golang-dev, dsymonds, bradfitz
CC=golang-dev
https://golang.org/cl/7323073

Also:
- faster code for example extraction
- simplify handling of command documentation:
  all "main" packages are treated as commands
- various minor cleanups along the way

For commands written in Go, any doc.go file containing
documentation must now be part of package main (rather
then package documentation), otherwise the documentation
won't show up in godoc (it will still build, though).

For commands written in C, documentation may still be
in doc.go files defining package documentation, but the
recommended way is to explicitly ignore those files with
a +build ignore constraint to define package main.

Fixes #4806.

R=adg, rsc, dave, bradfitz
CC=golang-dev
https://golang.org/cl/7333046

R=golang-dev, bradfitz, minux.ma
CC=golang-dev
https://golang.org/cl/7291043

This comment matches the one in path.

Fixes #4837.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7305100

side expression evaluation in assignment operations.

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/7349046

ref: http://www.dwarfstd.org/doc/DWARF4.pdf

Update #4829

R=minux.ma, iant
CC=dave, golang-dev
https://golang.org/cl/7354043