[dev.typeparams] cmd/compile: simplify ~r/~b naming

The compiler renames anonymous and blank result parameters to ~rN or
~bN, but the current semantics for computing N are rather annoying and
difficult to reproduce cleanly. They also lead to difficult to read
escape analysis results in tests.

This CL changes N to always be calculated as the parameter's index
within the function's result parameter tuple. E.g., if a function has
a single result, it will now always be named "~r0".

The normative change to this CL is fairly simple, but it requires
updating a lot of test expectations.

Change-Id: I58a3c94de00cb822cb94efe52d115531193c993c
Reviewed-on: https://go-review.googlesource.com/c/go/+/323010
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dan Scales <danscales@google.com>

3 files changed, 17 insertions, 18 deletions

diff --git a/src/cmd/compile/internal/logopt/logopt_test.go b/src/cmd/compile/internal/logopt/logopt_test.go
index 71976174b0..41a11b0c70 100644
--- a/src/cmd/compile/internal/logopt/logopt_test.go
+++ b/src/cmd/compile/internal/logopt/logopt_test.go
@@ -209,7 +209,7 @@ func s15a8(x *[15]int64) [15]int64 {
 		want(t, slogged, `{"range":{"start":{"line":11,"character":6},"end":{"line":11,"character":6}},"severity":3,"code":"isInBounds","source":"go compiler","message":""}`)
 		want(t, slogged, `{"range":{"start":{"line":7,"character":6},"end":{"line":7,"character":6}},"severity":3,"code":"canInlineFunction","source":"go compiler","message":"cost: 35"}`)
 		// escape analysis explanation
-		want(t, slogged, `{"range":{"start":{"line":7,"character":13},"end":{"line":7,"character":13}},"severity":3,"code":"leak","source":"go compiler","message":"parameter z leaks to ~r2 with derefs=0",`+
+		want(t, slogged, `{"range":{"start":{"line":7,"character":13},"end":{"line":7,"character":13}},"severity":3,"code":"leak","source":"go compiler","message":"parameter z leaks to ~r0 with derefs=0",`+
 			`"relatedInformation":[`+
 			`{"location":{"uri":"file://tmpdir/file.go","range":{"start":{"line":9,"character":13},"end":{"line":9,"character":13}}},"message":"escflow:    flow: y = z:"},`+
 			`{"location":{"uri":"file://tmpdir/file.go","range":{"start":{"line":9,"character":13},"end":{"line":9,"character":13}}},"message":"escflow:      from y := z (assign-pair)"},`+
@@ -220,7 +220,7 @@ func s15a8(x *[15]int64) [15]int64 {
 			`{"location":{"uri":"file://tmpdir/file.go","range":{"start":{"line":9,"character":13},"end":{"line":9,"character":13}}},"message":"escflow:      from \u0026y.b (address-of)"},`+
 			`{"location":{"uri":"file://tmpdir/file.go","range":{"start":{"line":4,"character":9},"end":{"line":4,"character":9}}},"message":"inlineLoc"},`+
 			`{"location":{"uri":"file://tmpdir/file.go","range":{"start":{"line":9,"character":13},"end":{"line":9,"character":13}}},"message":"escflow:      from ~R0 = \u0026y.b (assign-pair)"},`+
-			`{"location":{"uri":"file://tmpdir/file.go","range":{"start":{"line":9,"character":3},"end":{"line":9,"character":3}}},"message":"escflow:    flow: ~r2 = ~R0:"},`+
+			`{"location":{"uri":"file://tmpdir/file.go","range":{"start":{"line":9,"character":3},"end":{"line":9,"character":3}}},"message":"escflow:    flow: ~r0 = ~R0:"},`+
 			`{"location":{"uri":"file://tmpdir/file.go","range":{"start":{"line":9,"character":3},"end":{"line":9,"character":3}}},"message":"escflow:      from return (*int)(~R0) (return)"}]}`)
 	})
 }
diff --git a/src/cmd/compile/internal/noder/object.go b/src/cmd/compile/internal/noder/object.go
index a1a10e4eaa..581a3652ec 100644
--- a/src/cmd/compile/internal/noder/object.go
+++ b/src/cmd/compile/internal/noder/object.go
@@ -113,19 +113,21 @@ func (g *irgen) obj(obj types2.Object) *ir.Name {
 		}
 
 	case *types2.Var:
-		var sym *types.Sym
-		if class == ir.PPARAMOUT {
+		sym := g.sym(obj)
+		if class == ir.PPARAMOUT && (sym == nil || sym.IsBlank()) {
 			// Backend needs names for result parameters,
 			// even if they're anonymous or blank.
-			switch obj.Name() {
-			case "":
-				sym = typecheck.LookupNum("~r", len(ir.CurFunc.Dcl)) // 'r' for "result"
-			case "_":
-				sym = typecheck.LookupNum("~b", len(ir.CurFunc.Dcl)) // 'b' for "blank"
+			nresults := 0
+			for _, n := range ir.CurFunc.Dcl {
+				if n.Class == ir.PPARAMOUT {
+					nresults++
+				}
+			}
+			if sym == nil {
+				sym = typecheck.LookupNum("~r", nresults) // 'r' for "result"
+			} else {
+				sym = typecheck.LookupNum("~b", nresults) // 'b' for "blank"
 			}
-		}
-		if sym == nil {
-			sym = g.sym(obj)
 		}
 		name = g.objCommon(pos, ir.ONAME, sym, class, g.typ(obj.Type()))
 
diff --git a/src/cmd/compile/internal/typecheck/dcl.go b/src/cmd/compile/internal/typecheck/dcl.go
index f3058d8811..5f8b8b3d41 100644
--- a/src/cmd/compile/internal/typecheck/dcl.go
+++ b/src/cmd/compile/internal/typecheck/dcl.go
@@ -353,12 +353,10 @@ func funcargs(nt *ir.FuncType) {
 	}
 
 	// declare the out arguments.
-	gen := len(nt.Params)
-	for _, n := range nt.Results {
+	for i, n := range nt.Results {
 		if n.Sym == nil {
 			// Name so that escape analysis can track it. ~r stands for 'result'.
-			n.Sym = LookupNum("~r", gen)
-			gen++
+			n.Sym = LookupNum("~r", i)
 		}
 		if n.Sym.IsBlank() {
 			// Give it a name so we can assign to it during return. ~b stands for 'blank'.
@@ -367,8 +365,7 @@ func funcargs(nt *ir.FuncType) {
 			//	func g() int
 			// f is allowed to use a plain 'return' with no arguments, while g is not.
 			// So the two cases must be distinguished.
-			n.Sym = LookupNum("~b", gen)
-			gen++
+			n.Sym = LookupNum("~b", i)
 		}
 
 		funcarg(n, ir.PPARAMOUT)