CodeGen: Assert that inlined-at locations agree

As a follow-up to r234021, assert that a debug info intrinsic variable's
`MDLocalVariable::getInlinedAt()` always matches the
`MDLocation::getInlinedAt()` of its `!dbg` attachment.

The goal here is to get rid of `MDLocalVariable::getInlinedAt()`
entirely (PR22778), but I'll let these assertions bake for a while
first.

If you have an out-of-tree backend that just broke, you're probably
attaching the wrong `DebugLoc` to a `DBG_VALUE` instruction.  The one
you want is the location that was attached to the corresponding
`@llvm.dbg.declare` or `@llvm.dbg.value` call that you started with.

llvm-svn: 234038
diff --git a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
index 73061b6..8f504e1 100644
--- a/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -1131,6 +1131,8 @@
                                      false);
 
     if (Op) {
+      assert(DI->getVariable()->isValidLocationForIntrinsic(DbgLoc) &&
+             "Expected inlined-at fields to agree");
       if (Op->isReg()) {
         Op->setIsDebug(true);
         BuildMI(*FuncInfo.MBB, FuncInfo.InsertPt, DbgLoc,
@@ -1155,6 +1157,8 @@
     const DbgValueInst *DI = cast<DbgValueInst>(II);
     const MCInstrDesc &II = TII.get(TargetOpcode::DBG_VALUE);
     const Value *V = DI->getValue();
+    assert(DI->getVariable()->isValidLocationForIntrinsic(DbgLoc) &&
+           "Expected inlined-at fields to agree");
     if (!V) {
       // Currently the optimizer can produce this; insert an undef to
       // help debugging.  Probably the optimizer should not do this.