cmd/compile: delay expansion of OpArg until expand_calls

As it says, delay expanpsion of OpArg to the expand_calls phase,
to enable (eventually) interprocedural SSA optimizations, and
(sooner) change to a register ABI.

Includes a round of cleanup to function names and comments,
largely to match the expanded scope of the functions.

This CL removes the per-function dependence on GOSSAHASH,
but the go116lateCallExpansion kill switch remains (and was
tested locally to ensure it worked).

Two functions in expand_calls.go that performed overlapping
things were combined into a single function that is called
twice.

Fixes #42236.
For #40724.

Change-Id: Icbb78947eaa39f17f2c1210d5c2caef20abd6571
Reviewed-on: https://go-review.googlesource.com/c/go/+/262117
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

Author: dr2chase

src/cmd/compile/fmtmap_test.go

@@ -136,7 +136,6 @@ var knownFormats = map[string]string{
 	"cmd/compile/internal/types.EType %s":             "",
 	"cmd/compile/internal/types.EType %v":             "",
 	"cmd/internal/obj.ABI %v":                         "",
-	"cmd/internal/src.XPos %v":                        "",
 	"error %v":                                        "",
 	"float64 %.2f":                                    "",
 	"float64 %.3f":                                    "",

src/cmd/compile/internal/gc/ssa.go

@@ -409,11 +409,17 @@ func buildssa(fn *Node, worker int) *ssa.Func {
 
 	// Generate addresses of local declarations
 	s.decladdrs = map[*Node]*ssa.Value{}
+	var args []ssa.Param
+	var results []ssa.Param
 	for _, n := range fn.Func.Dcl {
 		switch n.Class() {
-		case PPARAM, PPARAMOUT:
+		case PPARAM:
+			s.decladdrs[n] = s.entryNewValue2A(ssa.OpLocalAddr, types.NewPtr(n.Type), n, s.sp, s.startmem)
+			args = append(args, ssa.Param{Type: n.Type, Offset: int32(n.Xoffset)})
+		case PPARAMOUT:
 			s.decladdrs[n] = s.entryNewValue2A(ssa.OpLocalAddr, types.NewPtr(n.Type), n, s.sp, s.startmem)
-			if n.Class() == PPARAMOUT && s.canSSA(n) {
+			results = append(results, ssa.Param{Type: n.Type, Offset: int32(n.Xoffset)})
+			if s.canSSA(n) {
 				// Save ssa-able PPARAMOUT variables so we can
 				// store them back to the stack at the end of
 				// the function.
@@ -4909,7 +4915,7 @@ func (s *state) canSSA(n *Node) bool {
 	if n.Class() == PPARAM && n.Sym != nil && n.Sym.Name == ".this" {
 		// wrappers generated by genwrapper need to update
 		// the .this pointer in place.
-		// TODO: treat as a PPARMOUT?
+		// TODO: treat as a PPARAMOUT?
 		return false
 	}
 	return canSSAType(n.Type)

src/cmd/compile/internal/ssa/compile.go

@@ -429,7 +429,7 @@ var passes = [...]pass{
 	{name: "early copyelim", fn: copyelim},
 	{name: "early deadcode", fn: deadcode}, // remove generated dead code to avoid doing pointless work during opt
 	{name: "short circuit", fn: shortcircuit},
-	{name: "decompose args", fn: decomposeArgs, required: true},
+	{name: "decompose args", fn: decomposeArgs, required: !go116lateCallExpansion, disabled: go116lateCallExpansion}, // handled by late call lowering
 	{name: "decompose user", fn: decomposeUser, required: true},
 	{name: "pre-opt deadcode", fn: deadcode},
 	{name: "opt", fn: opt, required: true},               // NB: some generic rules know the name of the opt pass. TODO: split required rules and optimizing rules

src/cmd/compile/internal/ssa/config.go

@@ -199,9 +199,9 @@ const (
 const go116lateCallExpansion = true
 
 // LateCallExpansionEnabledWithin returns true if late call expansion should be tested
-// within compilation of a function/method triggered by GOSSAHASH (defaults to "yes").
+// within compilation of a function/method.
 func LateCallExpansionEnabledWithin(f *Func) bool {
-	return go116lateCallExpansion && f.DebugTest // Currently set up for GOSSAHASH bug searches
+	return go116lateCallExpansion
 }
 
 // NewConfig returns a new configuration object for the given architecture.