cmd/internal/objfile: reuse tabwriter across symbols when disassembling

Since the tabwriter is flushed at every symbol,
it can be re-used with no impact on the output.

This cuts allocated space when objdump-ing
the compiler by almost 40%,
and enables further upcoming improvements.

It also speeds up objdump.

name            old time/op       new time/op       delta
ObjdumpCompile        9.22s ± 3%        8.77s ± 3%   -4.79%  (p=0.000 n=10+9)

Change-Id: Ief114d6c2680a4e762b5f439d3ca8dc7a89b9b27
Reviewed-on: https://go-review.googlesource.com/106978
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/cmd/internal/objfile/disasm.go b/src/cmd/internal/objfile/disasm.go
index 40f87e4869c52b11154b8dae40c9c0b0711ea586..deba7276951d02979e4bc8e8a5ebe189a1763550 100644 (file)
--- a/src/cmd/internal/objfile/disasm.go
+++ b/src/cmd/internal/objfile/disasm.go
@@ -197,6 +197,7 @@ func (d *Disasm) Print(w io.Writer, filter *regexp.Regexp, start, end uint64, pr
                fc = NewFileCache(8)
        }
 
+       tw := tabwriter.NewWriter(bw, 18, 8, 1, '\t', tabwriter.StripEscape)
        for _, sym := range d.syms {
                symStart := sym.Addr
                symEnd := sym.Addr + uint64(sym.Size)
@@ -215,7 +216,6 @@ func (d *Disasm) Print(w io.Writer, filter *regexp.Regexp, start, end uint64, pr
                file, _, _ := d.pcln.PCToLine(sym.Addr)
                fmt.Fprintf(bw, "TEXT %s(SB) %s\n", sym.Name, file)
 
-               tw := tabwriter.NewWriter(bw, 18, 8, 1, '\t', tabwriter.StripEscape)
                if symEnd > end {
                        symEnd = end
                }