[LAA] Also clear DiffChecks in LAI::reset().

DiffChecks will get populated twice when re-trying with runtime checks.
Without clearing it like the regular Checks vector, it will contain some
duplicates and the order the checks are created may not match the order
the checks have been queued when re-trying.

Author: fhahn

llvm/include/llvm/Analysis/LoopAccessAnalysis.h

@@ -486,6 +486,7 @@ class RuntimePointerChecking {
     Need = false;
     Pointers.clear();
     Checks.clear();
+    DiffChecks.clear();
   }
 
   /// Insert a pointer and calculate the start and end SCEVs.

llvm/test/Transforms/LoopVectorize/runtime-checks-difference-simplifications.ll

@@ -232,9 +232,9 @@ define void @check_creation_order(ptr %a, ptr %b, i32 %m) {
 ; CHECK-NEXT:    [[INVARIANT_GEP:%.*]] = getelementptr double, ptr [[A]], i64 [[M_EXT]]
 ; CHECK-NEXT:    br i1 false, label [[SCALAR_PH:%.*]], label [[VECTOR_MEMCHECK:%.*]]
 ; CHECK:       vector.memcheck:
-; CHECK-NEXT:    [[TMP0:%.*]] = sub i64 [[A1]], [[B2]]
+; CHECK-NEXT:    [[TMP0:%.*]] = mul nsw i64 [[M_EXT]], -8
 ; CHECK-NEXT:    [[DIFF_CHECK:%.*]] = icmp ult i64 [[TMP0]], 32
-; CHECK-NEXT:    [[TMP1:%.*]] = mul nsw i64 [[M_EXT]], -8
+; CHECK-NEXT:    [[TMP1:%.*]] = sub i64 [[A1]], [[B2]]
 ; CHECK-NEXT:    [[DIFF_CHECK3:%.*]] = icmp ult i64 [[TMP1]], 32
 ; CHECK-NEXT:    [[CONFLICT_RDX:%.*]] = or i1 [[DIFF_CHECK]], [[DIFF_CHECK3]]
 ; CHECK-NEXT:    br i1 [[CONFLICT_RDX]], label [[SCALAR_PH]], label [[VECTOR_PH:%.*]]