Revert "Ban address phis in non-OSSA as well"

This reverts commit 923c62c.

Author: meg-gupta

lib/SIL/Verifier/SILVerifier.cpp

@@ -985,6 +985,24 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
     return InstNumbers[a] < InstNumbers[b];
   }
 
+  // FIXME: For sanity, address-type phis should be prohibited at all SIL
+  // stages. However, the optimizer currently breaks the invariant in three
+  // places:
+  // 1. Normal Simplify CFG during conditional branch simplification
+  //    (sneaky jump threading).
+  // 2. Simplify CFG via Jump Threading.
+  // 3. Loop Rotation.
+  //
+  // BasicBlockCloner::canCloneInstruction and sinkAddressProjections is
+  // designed to avoid this issue, we just need to make sure all passes use it
+  // correctly.
+  //
+  // Minimally, we must prevent address-type phis as long as access markers are
+  // preserved. A goal is to preserve access markers in OSSA.
+  bool prohibitAddressPhis() {
+    return F.hasOwnership();
+  }
+
   void visitSILPhiArgument(SILPhiArgument *arg) {
     // Verify that the `isPhiArgument` property is sound:
     // - Phi arguments come from branches.
@@ -1008,7 +1026,7 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
                 "All phi argument inputs must be from branches.");
       }
     }
-    if (arg->isPhi()) {
+    if (arg->isPhi() && prohibitAddressPhis()) {
       // As a property of well-formed SIL, we disallow address-type
       // phis. Supporting them would prevent reliably reasoning about the
       // underlying storage of memory access. This reasoning is important for