[llvm] [LiveIntervals] Ignore artificial regs when adding kill flags (PR #116963)

[Matt Arsenault via llvm-commits]

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@@ -780,7 +783,7 @@ void LiveIntervals::addKillFlags(const VirtRegMap *VRM) {
         // are actually never written by %2. After assignment the <kill>
         // flag at the read instruction is invalid.
         LaneBitmask DefinedLanesMask;
-        if (LI.hasSubRanges()) {
+        if (LI.hasSubRanges() && TRI->getNumAllocatableSubRegs(PhysReg) > 1) {
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arsenm wrote:

I don't understand why this doesn't naturally fall out of the lanemasks for the register (e.g. above replace the TRI->regunits with MCRegUnitMaskIterator) 

https://github.com/llvm/llvm-project/pull/116963