Fix lifetime_dependence_borrow_fail diagnostic.

Report the correct variable name.

Author: atrick

SwiftCompilerSources/Sources/Optimizer/Utilities/LifetimeDependenceUtils.swift

@@ -597,6 +597,11 @@ struct VariableIntroducerUseDefWalker : LifetimeDependenceUseDefWalker {
     if let inst = value.definingInstruction, VariableScopeInstruction(inst) != nil {
       return introducer(value, owner)
     }
+    // Finding a variable introducer requires following the mark_dependence forwarded value, not the base value like the
+    // default LifetimeDependenceUseDefWalker.
+    if value is MarkDependenceInst {
+      return walkUpDefault(forwarded: value, owner)
+    }
     return walkUpDefault(dependent: value, owner: owner)
   }
 

test/SILOptimizer/lifetime_dependence/lifetime_dependence_borrow_fail.swift

@@ -77,10 +77,11 @@ func bv_incorrect_annotation2(_ w1: borrowing Wrapper, _ w2: borrowing Wrapper)
 }                                                                                                     // expected-note @-1{{this use causes the lifetime-dependent value to escape}}
 
 let ptr = UnsafeRawPointer(bitPattern: 1)!
-let nc = NC(ptr, 0) // expected-error {{lifetime-dependent variable 'nc' escapes its scope}}
+let nc = NC(ptr, 0)
 
 func bv_global(dummy: BV) -> BV {
-  nc.getBV()
+  nc.getBV()  // expected-error {{lifetime-dependent value escapes its scope}}
+  // expected-note @-4{{it depends on the lifetime of variable 'nc'}}
 } // expected-note {{this use causes the lifetime-dependent value to escape}}
 
 func testEmpty(nc: consuming NC) {