cmd/compile: add ideal int constants to dwarf

The core dump reader would like a bunch of ideal int
constants to be available in dwarf.

Makes the go binary 0.9% bigger.

Update #14517

Change-Id: I00cdfc7f53bcdc56fccba576c1d33010f03bdd95
Reviewed-on: https://go-review.googlesource.com/69270
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

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

@@ -219,14 +219,15 @@ func dumpGlobal(n *Node) {
 
 func dumpGlobalConst(n *Node) {
 	// only export typed constants
-	if n.Type == nil {
+	t := n.Type
+	if t == nil {
 		return
 	}
 	if n.Sym.Pkg != localpkg {
 		return
 	}
 	// only export integer constants for now
-	switch n.Type.Etype {
+	switch t.Etype {
 	case TINT8:
 	case TINT16:
 	case TINT32:
@@ -239,10 +240,20 @@ func dumpGlobalConst(n *Node) {
 	case TUINT:
 	case TUINTPTR:
 		// ok
+	case TIDEAL:
+		if !Isconst(n, CTINT) {
+			return
+		}
+		x := n.Val().U.(*Mpint)
+		if x.Cmp(minintval[TINT]) < 0 || x.Cmp(maxintval[TINT]) > 0 {
+			return
+		}
+		// Ideal integers we export as int (if they fit).
+		t = types.Types[TINT]
 	default:
 		return
 	}
-	Ctxt.DwarfIntConst(myimportpath, n.Sym.Name, typesymname(n.Type), n.Int64())
+	Ctxt.DwarfIntConst(myimportpath, n.Sym.Name, typesymname(t), n.Int64())
 }
 
 func dumpglobls() {

src/runtime/runtime-gdb_test.go

@@ -427,6 +427,7 @@ func TestGdbConst(t *testing.T) {
 		"-ex", "print main.largeConstant",
 		"-ex", "print main.minusOne",
 		"-ex", "print 'runtime._MSpanInUse'",
+		"-ex", "print 'runtime._PageSize'",
 		filepath.Join(dir, "a.exe"),
 	}
 	got, _ := exec.Command("gdb", args...).CombinedOutput()
@@ -435,7 +436,7 @@ func TestGdbConst(t *testing.T) {
 
 	t.Logf("output %q", sgot)
 
-	if !strings.Contains(sgot, "\n$1 = 42\n$2 = 18446744073709551615\n$3 = -1\n$4 = 1 '\\001'") {
+	if !strings.Contains(sgot, "\n$1 = 42\n$2 = 18446744073709551615\n$3 = -1\n$4 = 1 '\\001'\n$5 = 8192") {
 		t.Fatalf("output mismatch")
 	}
 }