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/RegAllocFast.cpp b/llvm/lib/CodeGen/RegAllocFast.cpp
index c6214140..dbf1a90 100644
--- a/llvm/lib/CodeGen/RegAllocFast.cpp
+++ b/llvm/lib/CodeGen/RegAllocFast.cpp
@@ -301,13 +301,9 @@
       const MDNode *Expr = DBG->getDebugExpression();
       bool IsIndirect = DBG->isIndirectDebugValue();
       uint64_t Offset = IsIndirect ? DBG->getOperand(1).getImm() : 0;
-      DebugLoc DL;
-      if (MI == MBB->end()) {
-        // If MI is at basic block end then use last instruction's location.
-        MachineBasicBlock::iterator EI = MI;
-        DL = (--EI)->getDebugLoc();
-      } else
-        DL = MI->getDebugLoc();
+      DebugLoc DL = DBG->getDebugLoc();
+      assert(DIVariable(Var)->isValidLocationForIntrinsic(DL) &&
+             "Expected inlined-at fields to agree");
       MachineInstr *NewDV =
           BuildMI(*MBB, MI, DL, TII->get(TargetOpcode::DBG_VALUE))
               .addFrameIndex(FI)
@@ -877,6 +873,8 @@
               const MDNode *Expr = MI->getDebugExpression();
               DebugLoc DL = MI->getDebugLoc();
               MachineBasicBlock *MBB = MI->getParent();
+              assert(DIVariable(Var)->isValidLocationForIntrinsic(DL) &&
+                     "Expected inlined-at fields to agree");
               MachineInstr *NewDV = BuildMI(*MBB, MBB->erase(MI), DL,
                                             TII->get(TargetOpcode::DBG_VALUE))
                                         .addFrameIndex(SS)