[PATCH] D40308: [RegisterCoalescer] More fixes for subreg join failure in RegCoalescer

[Matthias Braun via Phabricator via llvm-commits]

MatzeB accepted this revision.
MatzeB added a comment.
This revision is now accepted and ready to land.

LGTM, with same change to avoid unnecessary repeated shrinkToUses().



================
Comment at: lib/CodeGen/RegisterCoalescer.cpp:620-625
+  // Also deal with subranges
+  for (LiveInterval::SubRange &S : IntA.subranges()) {
+    LiveInterval::iterator SS = S.FindSegmentContaining(CopyUseIdx);
+    if (SS->end == CopyIdx)
+      shrinkToUses(&IntA);
+  }
----------------
You only ever need to do shrinkToUses once as it will deal with all subranges. Therefore I'd propose to change this block to:

```
  // Rewrite the copy.
  CopyMI->substituteRegister(IntA.reg, IntB.reg, 0, *TRI);
  // If the copy instruction was killing the destination register or any
  // subrange before the merge trim the live range.
  bool RecomputeLiveRange = AS->end == CopyIdx;
  if (!RecomputeLiveRange) {
    for (LiveInterval::SubRange &S : IntA.subranges()) {
      LiveInterval::iterator SS = S.FindSegmentContaining(CopyUseIdx);
      if (SS != S.end() && SS->end == CopyIdx) {
        RecomputeLiveRange = true;
        break;
      }
    }
  }
  if (RecomputeLiveRange)
    shrinkToUses(&IntA);
```


https://reviews.llvm.org/D40308