[LLVMdev] How to update LiveInterval information of newly inserted machine basic block

Haishan hndxvon at 163.com
Sun Jan 5 05:24:27 PST 2014

At 2014-01-05 03:28:22,"Andrew Trick" <atrick at apple.com> wrote:

On Jan 4, 2014, at 4:38 AM, Haishan <hndxvon at 163.com> wrote:

 At 2014-01-04 06:11:38,"Jakob Stoklund Olesen" <stoklund at 2pi.dk> wrote:

On Jan 3, 2014, at 1:52 PM, Andrew Trick <atrick at apple.com> wrote:

He really just wants to rerun LiveIntervals analysis, but LiveVariables is no longer available. Would it work just to clear all the intervals rerun LiveIntervals::computeVirtRegs after all the CFG transforms are complete?

Yes, I should think so.


Thank you very much for your talk.
I think I could append more information about updating LiveIntervals.
1. It works well if I just use from step1 to step3, without step4.
2. In step4, I firstly use UnreachableBlockElim pass to delete OldMBB.
Then, remove all intervals and recompute all the virtual registers' LiveIntervals.
3. I debug source code in LiveRangeCalc.cpp and copy partial code shown following.
/// LiveRangeCalc.cpp
#ifndef NDEBUG
    if (MBB->pred_empty()) {
      llvm_unreachable("Use not jointly dominated by defs.");
/// LiveRangeCalc.cpp
This MBB is the first block of MachineFunction. That's to say, This MBB doesn't have predecessor. It is reasonable?
From debug information, this unreachable error is generated from recompute a virtual register which isn't used or defined in this MBB. But this virtual register, in NewMBB,  is defined in a machine instruction which is copied from OldMBB.
So I am puzzled. 
Then, I do as Andy's suggestion, but it doesn't work, and it has same error.
Could you have any suggestion?
Thank you very much again.

Incrementally updating the live intervals will be complicated. You may be able to completely recompute them by clearing all VirtRegIntervals, then calling computeVirtRegs.


  Thank you very much for replying.
  I have some doubt about only using computeVirtRegs function to update LiveInterval.
  There are two other functions like "computeRegMasks() computeLiveInRegUnits()" in runOnMachineFunction of LiveIntervalAnalysis.cpp.
  So, I think that these two functions maybe effect updating LiveInterval information.
  What do you think of two functions?
  Thank you very much again.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20140105/7063fdaa/attachment.html>

More information about the llvm-dev mailing list