CSE/OSSA avoid endless cloning and reoptimization.

Prevent CSE from introducing useless copies, borrows, and
clones. Otherwise it will endlessly clone and re-cse the same
projections endlessly.

TODO: Most of these cases can be handled GuarateedOwnershipExtension
or extendOwnedLifetime without requiring any copies!

Author: atrick

lib/SILOptimizer/Transforms/CSE.cpp

@@ -1033,7 +1033,10 @@ bool CSE::processNode(DominanceInfoNode *Node) {
         OwnershipRAUWHelper helper(RAUWFixupContext,
                                    cast<SingleValueInstruction>(Inst),
                                    cast<SingleValueInstruction>(AvailInst));
-        if (!helper.isValid())
+        // If RAUW requires cloning the original, then there's no point. If it
+        // also requires introducing a copy and new borrow scope, then it's a
+        // very bad idea.
+        if (!helper.isValid() || helper.requiresCopyBorrowAndClone())
           continue;
         // Replace SingleValueInstruction using OSSA RAUW here
         nextI = helper.perform();

lib/SILOptimizer/Utils/OwnershipOptUtils.cpp

@@ -1041,10 +1041,9 @@ OwnershipRAUWHelper::replaceAddressUses(SingleValueInstruction *oldValue,
                                         SILValue newValue) {
   assert(oldValue->getType().isAddress() && newValue->getType().isAddress());
 
-  // If we are replacing addresses, see if we need to handle interior pointer
-  // fixups. If we don't have any extra info, then we know that we can just RAUW
-  // without any further work.
-  if (!ctx->extraAddressFixupInfo.base)
+  // If newValue was not generated by an interior pointer, then it cannot
+  // be within a borrow scope, so direct replacement works.
+  if (!requiresCopyBorrowAndClone())
     return replaceAllUsesAndErase(oldValue, newValue, ctx->callbacks);
 
   // We are RAUWing two addresses and we found that: