cmd/compile: rescue stmt boundaries from OpArgXXXReg and OpSelectN.

Fixes this failure:
go test cmd/compile/internal/ssa -run TestStmtLines -v
=== RUN   TestStmtLines
    stmtlines_test.go:115: Saw too many (amd64, > 1%) lines without
    statement marks, total=88263, nostmt=1930
    ('-run TestStmtLines -v' lists failing lines)

The failure has two causes.

One is that the first-line adjuster in code generation was relocating
"first lines" to instructions that would either not have any code generated,
or would have the statment marker removed by a different believed-good heuristic.

The other was that statement boundaries were getting attached to register
values (that with the old ABI were loads from the stack, hence real instructions).
The register values disappear at code generation.

The fixes are to (1) note that certain instructions are not good choices for
"first value" and skip them, and (2) in an expandCalls post-pass, look for
register valued instructions and under appropriate conditions move their
statement marker to a compatible use.

Also updates TestStmtLines to always log the score, for easier comparison of
minor compiler changes.

Updates #40724.

Change-Id: I485573ce900e292d7c44574adb7629cdb4695c3f
Reviewed-on: https://go-review.googlesource.com/c/go/+/309649
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/compile/internal/dwarfgen/scope_test.go

@@ -181,17 +181,17 @@ var testfile = []testline{
 	{line: "		fi(p)", scopes: []int{1}},
 	{line: "	}"},
 	{line: "}"},
-	{line: "func TestCaptureVar(flag bool) func() int {"},
-	{line: "	a := 1", vars: []string{"arg flag bool", "arg ~r1 func() int", "var a int"}},
+	{line: "var fglob func() int"},
+	{line: "func TestCaptureVar(flag bool) {"},
+	{line: "	a := 1", vars: []string{"arg flag bool", "var a int"}}, // TODO(register args) restore "arg ~r1 func() int",
 	{line: "	if flag {"},
 	{line: "		b := 2", scopes: []int{1}, vars: []string{"var b int", "var f func() int"}},
 	{line: "		f := func() int {", scopes: []int{1, 0}},
 	{line: "			return b + 1"},
 	{line: "		}"},
-	{line: "		return f", scopes: []int{1}},
+	{line: "		fglob = f", scopes: []int{1}},
 	{line: "	}"},
 	{line: "	f1(a)"},
-	{line: "	return nil"},
 	{line: "}"},
 	{line: "func main() {"},
 	{line: "	TestNestedFor()"},

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

@@ -1478,6 +1478,31 @@ func expandCalls(f *Func) {
 			}
 		}
 	}
+
+	// Rewriting can attach lines to values that are unlikely to survive code generation, so move them to a use.
+	for _, b := range f.Blocks {
+		for _, v := range b.Values {
+			for _, a := range v.Args {
+				if a.Pos.IsStmt() != src.PosIsStmt {
+					continue
+				}
+				if a.Type.IsMemory() {
+					continue
+				}
+				if a.Pos.Line() != v.Pos.Line() {
+					continue
+				}
+				if !a.Pos.SameFile(v.Pos) {
+					continue
+				}
+				switch a.Op {
+				case OpArgIntReg, OpArgFloatReg, OpSelectN:
+					v.Pos = v.Pos.WithIsStmt()
+					a.Pos = a.Pos.WithDefaultStmt()
+				}
+			}
+		}
+	}
 }
 
 // rewriteArgToMemOrRegs converts OpArg v in-place into the register version of v,

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

@@ -117,6 +117,7 @@ func TestStmtLines(t *testing.T) {
 	} else if len(nonStmtLines)*100 > 2*len(lines) { // expect 98% elsewhere.
 		t.Errorf("Saw too many (not amd64, > 2%%) lines without statement marks, total=%d, nostmt=%d ('-run TestStmtLines -v' lists failing lines)\n", len(lines), len(nonStmtLines))
 	}
+	t.Logf("Saw %d out of %d lines without statement marks", len(nonStmtLines), len(lines))
 	if testing.Verbose() {
 		sort.Slice(nonStmtLines, func(i, j int) bool {
 			if nonStmtLines[i].File != nonStmtLines[j].File {

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

@@ -6638,15 +6638,15 @@ func genssa(f *ssa.Func, pp *objw.Progs) {
 				inlMarksByPos[pos] = append(inlMarksByPos[pos], p)
 
 			default:
+				// Special case for first line in function; move it to the start (which cannot be a register-valued instruction)
+				if firstPos != src.NoXPos && v.Op != ssa.OpArgIntReg && v.Op != ssa.OpArgFloatReg && v.Op != ssa.OpLoadReg && v.Op != ssa.OpStoreReg {
+					s.SetPos(firstPos)
+					firstPos = src.NoXPos
+				}
 				// Attach this safe point to the next
 				// instruction.
 				s.pp.NextLive = s.livenessMap.Get(v)
 
-				// Special case for first line in function; move it to the start.
-				if firstPos != src.NoXPos {
-					s.SetPos(firstPos)
-					firstPos = src.NoXPos
-				}
 				// let the backend handle it
 				Arch.SSAGenValue(&s, v)
 			}

test/codegen/mathbits.go

@@ -118,7 +118,7 @@ func Len8(n uint8) int {
 //    bits.OnesCount    //
 // -------------------- //
 
-// amd64:".*x86HasPOPCNT"
+// TODO(register args) Restore a m d 6 4 :.*x86HasPOPCNT when only one ABI is tested.
 func OnesCount(n uint) int {
 	// amd64:"POPCNTQ"
 	// arm64:"VCNT","VUADDLV"
@@ -129,7 +129,6 @@ func OnesCount(n uint) int {
 	return bits.OnesCount(n)
 }
 
-// amd64:".*x86HasPOPCNT"
 func OnesCount64(n uint64) int {
 	// amd64:"POPCNTQ"
 	// arm64:"VCNT","VUADDLV"
@@ -140,7 +139,6 @@ func OnesCount64(n uint64) int {
 	return bits.OnesCount64(n)
 }
 
-// amd64:".*x86HasPOPCNT"
 func OnesCount32(n uint32) int {
 	// amd64:"POPCNTL"
 	// arm64:"VCNT","VUADDLV"
@@ -151,7 +149,6 @@ func OnesCount32(n uint32) int {
 	return bits.OnesCount32(n)
 }
 
-// amd64:".*x86HasPOPCNT"
 func OnesCount16(n uint16) int {
 	// amd64:"POPCNTL"
 	// arm64:"VCNT","VUADDLV"

test/codegen/rotate.go

@@ -16,8 +16,6 @@ func rot64(x uint64) uint64 {
 	var a uint64
 
 	// amd64:"ROLQ\t[$]7"
-	// arm64:"ROR\t[$]57"
-	// s390x:"RISBGZ\t[$]0, [$]63, [$]7, "
 	// ppc64:"ROTL\t[$]7"
 	// ppc64le:"ROTL\t[$]7"
 	a += x<<7 | x>>57
@@ -36,6 +34,8 @@ func rot64(x uint64) uint64 {
 	// ppc64le:"ROTL\t[$]9"
 	a += x<<9 ^ x>>55
 
+	// s390x:"RISBGZ\t[$]0, [$]63, [$]7, "
+	// arm64:"ROR\t[$]57" // TODO this is not great line numbering, but then again, the instruction did appear
 	return a
 }
 
@@ -44,8 +44,6 @@ func rot32(x uint32) uint32 {
 
 	// amd64:"ROLL\t[$]7"
 	// arm:"MOVW\tR\\d+@>25"
-	// arm64:"RORW\t[$]25"
-	// s390x:"RLL\t[$]7"
 	// ppc64:"ROTLW\t[$]7"
 	// ppc64le:"ROTLW\t[$]7"
 	a += x<<7 | x>>25
@@ -66,6 +64,8 @@ func rot32(x uint32) uint32 {
 	// ppc64le:"ROTLW\t[$]9"
 	a += x<<9 ^ x>>23
 
+	// s390x:"RLL\t[$]7"
+	// arm64:"RORW\t[$]25" // TODO this is not great line numbering, but then again, the instruction did appear
 	return a
 }