all: rewrite goroutine lowering

Before this commit, goroutine support was spread through the compiler.
This commit changes this support, so that the compiler itself only
generates simple intrinsics and leaves the real support to a compiler
pass that runs as one of the TinyGo-specific optimization passes.

The biggest change, that was done together with the rewrite, was support
for goroutines in WebAssembly for JavaScript. The challenge in
JavaScript is that in general no blocking operations are allowed, which
means that programs that call time.Sleep() but do not start goroutines
also have to be scheduled by the scheduler.

ir/ir.go

@@ -18,31 +18,26 @@ import (
 // View on all functions, types, and globals in a program, with analysis
 // results.
 type Program struct {
-	Program        *ssa.Program
-	LoaderProgram  *loader.Program
-	mainPkg        *ssa.Package
-	Functions      []*Function
-	functionMap    map[*ssa.Function]*Function
-	Globals        []*Global
-	globalMap      map[*ssa.Global]*Global
-	comments       map[string]*ast.CommentGroup
-	NamedTypes     []*NamedType
-	needsScheduler bool
-	goCalls        []*ssa.Go
+	Program       *ssa.Program
+	LoaderProgram *loader.Program
+	mainPkg       *ssa.Package
+	Functions     []*Function
+	functionMap   map[*ssa.Function]*Function
+	Globals       []*Global
+	globalMap     map[*ssa.Global]*Global
+	comments      map[string]*ast.CommentGroup
+	NamedTypes    []*NamedType
 }
 
 // Function or method.
 type Function struct {
 	*ssa.Function
 	LLVMFn    llvm.Value
-	linkName  string      // go:linkname, go:export, go:interrupt
-	exported  bool        // go:export
-	nobounds  bool        // go:nobounds
-	blocking  bool        // calculated by AnalyseBlockingRecursive
-	flag      bool        // used by dead code elimination
-	interrupt bool        // go:interrupt
-	parents   []*Function // calculated by AnalyseCallgraph
-	children  []*Function // calculated by AnalyseCallgraph
+	linkName  string // go:linkname, go:export, go:interrupt
+	exported  bool   // go:export
+	nobounds  bool   // go:nobounds
+	flag      bool   // used by dead code elimination
+	interrupt bool   // go:interrupt
 }
 
 // Global variable, possibly constant.