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cmd/compile: more compact DWARF location for locals and arguments

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Now that all functions have a DW_AT_frame_base defined we can use
DW_OP_fbreg to specify the location of variables and formal parameters,
instead of the DW_OP_call_frame_cfa/DW_OP_consts/DW_OP_plus, saving 2
bytes for every variable and 2 bytes for every formal parameter after
the first one.

Change-Id: I2c7395b67e4a814a0131ab1520df11ca48ff9327
Reviewed-on: https://go-review.googlesource.com/60550
Run-TryBot: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
This commit is contained in:
Alessandro Arzilli 2017-07-04 08:32:02 +02:00 committed by Heschi Kreinick
parent 84188296e9
commit 31ddd8a39d
1 changed files with 12 additions and 6 deletions
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18
src/cmd/internal/dwarf/dwarf.go
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@ -804,12 +804,14 @@ func putvar(ctxt Context, info, loc Sym, v *Var, startPC Sym, encbuf []byte) {
putattr(ctxt, info, v.Abbrev, DW_FORM_sec_offset, DW_CLS_PTR, int64(loc.Len()), loc)
addLocList(ctxt, loc, startPC, v, encbuf)
} else {
loc := append(encbuf[:0], DW_OP_call_frame_cfa)
if v.StackOffset != 0 {
loc = append(loc, DW_OP_consts)
loc := encbuf[:0]
if v.StackOffset == 0 {
loc = append(loc, DW_OP_call_frame_cfa)
} else {
loc = append(loc, DW_OP_fbreg)
loc = AppendSleb128(loc, int64(v.StackOffset))
loc = append(loc, DW_OP_plus)
}
putattr(ctxt, info, v.Abbrev, DW_FORM_block1, DW_CLS_BLOCK, int64(len(loc)), loc)
}
putattr(ctxt, info, v.Abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, v.Type)
@ -826,8 +828,12 @@ func addLocList(ctxt Context, listSym, startPC Sym, v *Var, encbuf []byte) {
for _, piece := range entry.Pieces {
if !piece.Missing {
if piece.OnStack {
locBuf = append(locBuf, DW_OP_fbreg)
locBuf = AppendSleb128(locBuf, int64(piece.StackOffset))
if piece.StackOffset == 0 {
locBuf = append(locBuf, DW_OP_call_frame_cfa)
} else {
locBuf = append(locBuf, DW_OP_fbreg)
locBuf = AppendSleb128(locBuf, int64(piece.StackOffset))
}
} else {
if piece.RegNum < 32 {
locBuf = append(locBuf, DW_OP_reg0+byte(piece.RegNum))