577764 - TM: avoid a dead guard at the end of loop fragments

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Nicholas Nethercote [inactive]]

Attachment: patch

Loop fragments always look something like this:

      ebx = parami 0 ebx
      esi = parami 1 esi
      edi = parami 2 edi
      state = parami 0 ecx
      label1:
      ...
      lti1 = lti addxovi1, immi1/*......*/
      xf1: xf lti1 -> pc=...... imacpc=0x0 sp+16 rp+0 (GuardID=003)
      j -> label1
      livei state
      x1: x  -> pc=...... imacpc=0x0 sp+0 rp+0 (GuardID=004)

That guard at the end is dead.  This patch removes it.  This doesn't save much  perf-wise -- just the processing and storing of a single guard at compile-time.  But it saves me the mental effort of having to ignore it :)

Comment 1

[Nicholas Nethercote [inactive]]

It'll also make things a tiny bit easier for LICM (bug 545406).

Comment 2

[Nicholas Nethercote [inactive]]

http://hg.mozilla.org/tracemonkey/rev/cf557e3fc53d

Comment 3

[Robert Sayre]

http://hg.mozilla.org/mozilla-central/rev/cf557e3fc53d

Comment 4

[Boris Zbarsky [:bzbarsky]]

This looks like it caused bug 582766.