CopyToBorrowOptimization: need to update borrowed-from instructions when changes are made

When ownership is changed from owned to guaranteed, the enclosing values of a guaranteed value can change.
Fixes a SIL verifier error.

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/CopyToBorrowOptimization.swift

@@ -53,49 +53,60 @@ let copyToBorrowOptimization = FunctionPass(name: "copy-to-borrow-optimization")
     return
   }
 
+  var changed = false
+
   for inst in function.instructions {
     switch inst {
     case let load as LoadInst:
-      optimize(load: load, context)
+      if optimize(load: load, context) {
+        changed = true
+      }
     case let copy as CopyValueInst:
-      optimize(copy: copy, context)
+      if optimize(copy: copy, context) {
+        changed = true
+      }
     default:
       break
     }
   }
+
+  if changed {
+    updateBorrowedFrom(in: function, context)
+  }
 }
 
-private func optimize(load: LoadInst, _ context: FunctionPassContext) {
+private func optimize(load: LoadInst, _ context: FunctionPassContext) -> Bool {
   if load.loadOwnership != .copy {
-    return
+    return false
   }
 
   var collectedUses = Uses(context)
   defer { collectedUses.deinitialize() }
   if !collectedUses.collectUses(of: load) {
-    return
+    return false
   }
 
   if mayWrite(toAddressOf: load,
               within: collectedUses.destroys,
               usersInDeadEndBlocks: collectedUses.usersInDeadEndBlocks,
               context)
   {
-    return
+    return false
   }
 
   load.replaceWithLoadBorrow(collectedUses: collectedUses)
+  return true
 }
 
-private func optimize(copy: CopyValueInst, _ context: FunctionPassContext) {
+private func optimize(copy: CopyValueInst, _ context: FunctionPassContext) -> Bool {
   if copy.fromValue.ownership != .guaranteed {
-    return
+    return false
   }
 
   var collectedUses = Uses(context)
   defer { collectedUses.deinitialize() }
   if !collectedUses.collectUses(of: copy) {
-    return
+    return false
   }
 
   var liverange = InstructionRange(begin: copy, context)
@@ -104,10 +115,11 @@ private func optimize(copy: CopyValueInst, _ context: FunctionPassContext) {
   liverange.insert(contentsOf: collectedUses.usersInDeadEndBlocks)
 
   if !liverange.isFullyContainedIn(borrowScopeOf: copy.fromValue.lookThroughForwardingInstructions) {
-    return
+    return false
   }
 
   remove(copy: copy, collectedUses: collectedUses, liverange: liverange)
+  return true
 }
 
 private struct Uses {

test/SILOptimizer/copy-to-borrow-optimization.sil

@@ -2275,3 +2275,22 @@ bb1(%6 : @guaranteed $MyArrayStorageBase):
   %13 = tuple ()
   return %13
 }
+
+// CHECK-LABEL: sil [ossa] @test_updating_borrowed_from :
+// CHECK:         borrowed {{.*}} from (%0)
+// CHECK-LABEL: } // end sil function 'test_updating_borrowed_from'
+sil [ossa] @test_updating_borrowed_from : $@convention(thin) (@guaranteed NonTrivialStruct) -> () {
+bb0(%0 : @guaranteed $NonTrivialStruct):
+  %1 = destructure_struct %0 : $NonTrivialStruct
+  %2 = copy_value %1 : $Klass
+  %3 = begin_borrow %2 : $Klass
+  br bb1(%3 : $Klass)
+
+bb1(%5 : @reborrow $Klass):
+  %6 = borrowed %5 : $Klass from (%2 : $Klass)
+  end_borrow %6 : $Klass
+  destroy_value %2 : $Klass
+  %9 = tuple ()
+  return %9 : $()
+}
+