[llvm] [LV] Create block in mask up-front if needed. (PR #76635)

[via llvm-commits]

================
@@ -120,6 +120,7 @@ bool VPRecipeBase::mayHaveSideEffects() const {
     return false;
   case VPInstructionSC:
     switch (cast<VPInstruction>(this)->getOpcode()) {
+    case Instruction::Or:
----------------
ayalz wrote:

Fix independent of this patch?
Worth noting somewhere that the default is conservative, and should be revisited when new ones are introduced?

https://github.com/llvm/llvm-project/pull/76635