[llvm] [SPIR-V] Fix BB ordering & register lifetime (PR #111026)

[Nathan Gauër via llvm-commits]

================
@@ -87,6 +87,8 @@ BasicBlock *getExitFor(const ConvergenceRegion *CR) {
 // Returns the merge block designated by I if I is a merge instruction, nullptr
 // otherwise.
 BasicBlock *getDesignatedMergeBlock(Instruction *I) {
+  if (I == nullptr)
+    return nullptr;
----------------
Keenuts wrote:

done

https://github.com/llvm/llvm-project/pull/111026