[llvm] [VPlan] Model branch cond to enter scalar epilogue in VPlan. (PR #92651)

[Florian Hahn via llvm-commits]

================
@@ -18,8 +18,12 @@ define i32 @read_only_loop_with_runtime_check(ptr noundef %array, i32 noundef %c
 ; CHECK:       for.body.preheader10:
 ; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i32 [[N]], 8
 ; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label [[FOR_BODY_PREHEADER13:%.*]], label [[VECTOR_PH:%.*]]
+; CHECK:       for.body.preheader13:
+; CHECK-NEXT:    [[INDVARS_IV_PH:%.*]] = phi i64 [ 0, [[FOR_BODY_PREHEADER10]] ], [ [[N_VEC:%.*]], [[MIDDLE_BLOCK:%.*]] ]
+; CHECK-NEXT:    [[SUM_07_PH:%.*]] = phi i32 [ 0, [[FOR_BODY_PREHEADER10]] ], [ [[TMP7:%.*]], [[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
----------------
fhahn wrote:

changes to the input was left over from debugging, restored, thanks!

https://github.com/llvm/llvm-project/pull/92651