[VPlan] Address review

Author: artagnon

llvm/lib/Transforms/Vectorize/VPlanUtils.cpp

@@ -113,7 +113,12 @@ bool vputils::isUniformAcrossVFsAndUFs(VPValue *V) {
   return TypeSwitch<const VPRecipeBase *, bool>(R)
       .Case<VPDerivedIVRecipe>([](const auto *R) { return true; })
       .Case<VPReplicateRecipe>([](const auto *R) {
+        // Be conservative about side-effects, except for the
+        // known-side-effecting assumes and stores, which we know will be
+        // uniform.
         return R->isSingleScalar() &&
+               (!R->mayHaveSideEffects() ||
+                isa<AssumeInst, StoreInst>(R->getUnderlyingInstr())) &&
                all_of(R->operands(), isUniformAcrossVFsAndUFs);
       })
       .Case<VPInstruction>([](const auto *VPI) {