[LiveRange] Verify Other LiveRange in Join API

[annamthomas]

The LiveRange::join API takes in two live ranges. We should verify the
LiveRange passed in to the Join API as well.

[llvmbot]

@llvm/pr-subscribers-llvm-regalloc

Changes

The LiveRange::join API takes in two live ranges. We should verify the
LiveRange argument passed in as well.

---

Full diff: https://github.com/llvm/llvm-project/pull/66809.diff

1 Files Affected:

• (modified) llvm/lib/CodeGen/LiveInterval.cpp (+1)

diff --git a/llvm/lib/CodeGen/LiveInterval.cpp b/llvm/lib/CodeGen/LiveInterval.cpp
index 1cf354349c5610c..a8e45d46c07cee6 100644
--- a/llvm/lib/CodeGen/LiveInterval.cpp
+++ b/llvm/lib/CodeGen/LiveInterval.cpp
@@ -629,6 +629,7 @@ void LiveRange::join(LiveRange &Other,
                      const int *RHSValNoAssignments,
                      SmallVectorImpl<VNInfo *> &NewVNInfo) {
   verify();
+  Other.verify();
 
   // Determine if any of our values are mapped.  This is uncommon, so we want
   // to avoid the range scan if not.

[annamthomas]

Just for context, this came up because we saw a crash in LiveRange::join() which cannot be reproduced and we do not have debugInfo on the core.

When cross-referencing the asm of the function to the source code, we see the crash is in this code, with S.valno being null:

// Rewrite Other values before changing the VNInfo ids.
  // This can leave Other in an invalid state because we're not coalescing
  // touching segments that now have identical values. That's OK since Other is
  // not supposed to be valid after calling join();
  for (Segment &S : Other.segments)
    S.valno = NewVNInfo[RHSValNoAssignments[S.valno->id]];

With Verify() run onOther LiveRange, this will be caught.

[andykaylor]

Looks reasonable