Tag cached interference with a user-provided tag instead of the virtual register number.

The live range of a virtual register may change which invalidates the cached
interference information.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127772 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/RegAllocBasic.cpp b/lib/CodeGen/RegAllocBasic.cpp
index d51be52..ce92f3d 100644
--- a/lib/CodeGen/RegAllocBasic.cpp
+++ b/lib/CodeGen/RegAllocBasic.cpp
@@ -296,6 +296,9 @@
       continue;
     }
 
+    // Invalidate all interference queries, live ranges could have changed.
+    ++UserTag;
+
     // selectOrSplit requests the allocator to return an available physical
     // register if possible and populate a list of new live intervals that
     // result from splitting.