cmd/compile: call fieldtrack after flushing Progs

Fixes #20014

Change-Id: Ie58d3e989f2d7388b3d8849fbcfbceed3c6aa084
Reviewed-on: https://go-review.googlesource.com/41132
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -211,12 +211,13 @@ func compile(fn *Node) {
 	ssafn := buildssa(fn)
 	pp := newProgs(fn)
 	genssa(ssafn, pp)
-	fieldtrack(pp.Text.From.Sym, fn.Func.FieldTrack)
 	if pp.Text.To.Offset < 1<<31 {
 		pp.Flush()
 	} else {
 		largeStackFrames = append(largeStackFrames, fn.Pos)
 	}
+	// fieldtrack must be called after pp.Flush. See issue 20014.
+	fieldtrack(pp.Text.From.Sym, fn.Func.FieldTrack)
 	pp.Free()
 }