Update SILGen for borrow accessors under library evolution

Under library evolution, loadable self arguments are passed as @in_guaranteed.
SILGen generates load_borrow for such self arguments proactively.
load_borrow creates an artifical scope and returning values produced within this scope
will be illegal without resorting to unsafe operations today.

This change avoids creating a load_borrow proactively for borrow accessors.

Author: meg-gupta

lib/SILGen/SILGenApply.cpp

@@ -7306,12 +7306,16 @@ bool AccessorBaseArgPreparer::shouldLoadBaseAddress() const {
     return base.isLValue() || base.isPlusZeroRValueOrTrivial()
       || !SGF.silConv.useLoweredAddresses();
 
-  case ParameterConvention::Indirect_In_Guaranteed:
+  case ParameterConvention::Indirect_In_Guaranteed: {
+    if (accessor.isBorrowAccessor()) {
+      return false;
+    }
     // We can pass the memory we already have at +0. The memory referred to
     // by the base should be already immutable unless it was lowered as an
     // lvalue.
     return base.isLValue()
       || !SGF.silConv.useLoweredAddresses();
+  }
 
   // If the accessor wants the value directly, we definitely have to
   // load.

lib/SILGen/SILGenProlog.cpp

@@ -728,13 +728,15 @@ class ArgumentInitHelper {
                                         : AbstractionPattern(substType));
 
       // A parameter can be directly marked as addressable, or its
-      // addressability can be implied by a scoped dependency.
-      bool isAddressable = false;
-      
-      isAddressable = pd->isAddressable()
-        || (ScopedDependencies.contains(pd)
-            && SGF.getTypeProperties(origType, substType)
-                  .isAddressableForDependencies());
+      // addressability can be implied by a scoped dependency or a borrow
+      // dependency.
+      bool isAddressable =
+          pd->isAddressable() ||
+          (ScopedDependencies.contains(pd) &&
+           SGF.getTypeProperties(origType, substType)
+               .isAddressableForDependencies()) ||
+          SGF.getFunction().getConventions().hasGuaranteedAddressResult() ||
+          SGF.getFunction().getConventions().hasGuaranteedResult();
       paramValue = argEmitter.handleParam(origType, substType, pd,
                                           isAddressable);
     }