[LV] Invalidate cost model decisions along with interleave groups.

Cost-modeling decisions are tied to the compute interleave groups
(widening decisions, scalar and uniform values). When invalidating the
interleave groups, those decisions also need to be invalidated.

Otherwise there is a mis-match during VPlan construction.
VPWidenMemoryRecipes created initially are left around w/o converting them
into VPInterleave recipes. Such a conversion indeed should not take place,
and these gather/scatter recipes may in fact be right. The crux is leaving around
obsolete CM_Interleave (and dependent) markings of instructions along with
their costs, instead of recalculating decisions, costs, and recipes.

Alternatively to forcing a complete recompute later on, we could try
to selectively invalidate the decisions connected to the interleave
groups. But we would likely need to run the uniform/scalar value
detection parts again anyways and the extra complexity is probably not
worth it.

Fixes PR45572.

Reviewers: gilr, rengolin, Ayal, hsaito

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D78298

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/VectorUtils.cpp b/llvm/lib/Analysis/VectorUtils.cpp
index 0d41148..7cbcb17 100644
--- a/llvm/lib/Analysis/VectorUtils.cpp
+++ b/llvm/lib/Analysis/VectorUtils.cpp
@@ -1243,6 +1243,8 @@ void InterleavedAccessInfo::invalidateGroupsRequiringScalarEpilogue() {
     if (Group->requiresScalarEpilogue())
       DelSet.insert(Group);
   }
+  assert(!DelSet.empty() && "At least one group must be invalidated, as a "
+                            "scalar epilogue was required");
   for (auto *Ptr : DelSet) {
     LLVM_DEBUG(
         dbgs()