Update SideEffects for borrow accessors returning addresses

Add a read effect on the self parameter. Without this, the self parameter can get dead code eliminated by the GenericSpecializer.

Author: meg-gupta

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/ComputeSideEffects.swift

@@ -254,6 +254,11 @@ private struct CollectedEffects {
       // effect, it would not give any significant benefit in any of our current optimizations.
       addEffects(.destroy, to: inst.operands[0].value, fromInitialPath: SmallProjectionPath(.anyValueFields))
 
+    case is ReturnInst:
+      if inst.parentFunction.convention.hasGuaranteedAddressResult {
+        addEffects(.read, to: inst.operands[0].value)
+      }
+
     default:
       if inst.mayRelease {
         globalEffects = .worstEffects

SwiftCompilerSources/Sources/SIL/FunctionConvention.swift

@@ -98,6 +98,20 @@ public struct FunctionConvention : CustomStringConvertible {
     return SILFunctionType_getLifetimeDependencies(functionType.bridged).count() != 0
   }
 
+  public var hasGuaranteedResult: Bool {
+    if results.count != 1 {
+      return false
+    }
+    return results[0].convention == .guaranteed
+  }
+
+  public var hasGuaranteedAddressResult: Bool {
+    if results.count != 1 {
+      return false
+    }
+    return results[0].convention == .guaranteedAddress
+  }
+
   public var description: String {
     var str = functionType.description
     for paramIdx in 0..<parameters.count {