[region-isolation] Propagate through the whole source operand instead of just the representative of the source value when constructing assign and merge.

This will let me know the exact source operand used instead of the source value
representative. This will ensure that the name associated with the diagnostic is
not of the representative value, but the actual value that was the source of the
assign.

This is an NFCI commit that is an algebraic refactor.

(cherry picked from commit ae797d4)

Author: gottesmm

include/swift/SIL/InstWrappers.h

@@ -221,6 +221,13 @@ class SelectEnumOperation {
       return sei->getCase(i);
     return value.get<SelectEnumAddrInst *>()->getCase(i);
   }
+
+  std::pair<EnumElementDecl *, Operand *> getCaseOperand(unsigned i) const {
+    if (auto *sei = value.dyn_cast<SelectEnumInst *>())
+      return sei->getCaseOperand(i);
+    return value.get<SelectEnumAddrInst *>()->getCaseOperand(i);
+  }
+
   /// Return the value that will be used as the result for the specified enum
   /// case.
   SILValue getCaseResult(EnumElementDecl *D) {
@@ -229,6 +236,12 @@ class SelectEnumOperation {
     return value.get<SelectEnumAddrInst *>()->getCaseResult(D);
   }
 
+  Operand *getCaseResultOperand(EnumElementDecl *D) {
+    if (auto *sei = value.dyn_cast<SelectEnumInst *>())
+      return sei->getCaseResultOperand(D);
+    return value.get<SelectEnumAddrInst *>()->getCaseResultOperand(D);
+  }
+
   /// If the default refers to exactly one case decl, return it.
   NullablePtr<EnumElementDecl> getUniqueCaseForDefault();
 
@@ -243,6 +256,12 @@ class SelectEnumOperation {
       return sei->getDefaultResult();
     return value.get<SelectEnumAddrInst *>()->getDefaultResult();
   }
+
+  Operand *getDefaultResultOperand() const {
+    if (auto *sei = value.dyn_cast<SelectEnumInst *>())
+      return sei->getDefaultResultOperand();
+    return value.get<SelectEnumAddrInst *>()->getDefaultResultOperand();
+  }
 };
 
 class ForwardingOperation {

include/swift/SIL/SILInstruction.h

@@ -7018,6 +7018,12 @@ class SelectEnumInstBase : public BaseTy {
                           getAllOperands()[i+1].get());
   }
 
+  std::pair<EnumElementDecl *, Operand *> getCaseOperand(unsigned i) const {
+    auto *self = const_cast<SelectEnumInstBase *>(this);
+    return std::make_pair(getEnumElementDeclStorage()[i],
+                          &self->getAllOperands()[i + 1]);
+  }
+
   /// Return the value that will be used as the result for the specified enum
   /// case.
   SILValue getCaseResult(EnumElementDecl *D) {
@@ -7030,6 +7036,18 @@ class SelectEnumInstBase : public BaseTy {
     return getDefaultResult();
   }
 
+  Operand *getCaseResultOperand(EnumElementDecl *D) {
+    for (unsigned i = 0, e = getNumCases(); i != e; ++i) {
+      auto Entry = getCaseOperand(i);
+      if (Entry.first == D)
+        return Entry.second;
+    }
+
+    // select_enum is required to be fully covered, so return the default if we
+    // didn't find anything.
+    return getDefaultResultOperand();
+  }
+
   bool hasDefault() const {
     return sharedUInt8().SelectEnumInstBase.hasDefault;
   }
@@ -7039,6 +7057,12 @@ class SelectEnumInstBase : public BaseTy {
     return getAllOperands().back().get();
   }
 
+  Operand *getDefaultResultOperand() const {
+    assert(hasDefault() && "doesn't have a default");
+    auto *self = const_cast<SelectEnumInstBase *>(this);
+    return &self->getAllOperands().back();
+  }
+
   unsigned getNumCases() const {
     return getAllOperands().size() - 1 - hasDefault();
   }

include/swift/SILOptimizer/Utils/PartitionUtils.h

@@ -510,15 +510,23 @@ class PartitionOp {
            "Transfer needs a sourceInst");
   }
 
+  PartitionOp(PartitionOpKind opKind, Element arg1, Element arg2,
+              Operand *sourceOp = nullptr)
+      : opKind(opKind), opArgs({arg1, arg2}), source(sourceOp) {
+    assert((opKind == PartitionOpKind::Assign ||
+            opKind == PartitionOpKind::Merge) &&
+           "Only supported for assign and merge");
+  }
+
   PartitionOp(PartitionOpKind opKind, SILInstruction *sourceInst)
       : opKind(opKind), opArgs(), source(sourceInst) {}
 
   friend class Partition;
 
 public:
-  static PartitionOp Assign(Element tgt, Element src,
-                            SILInstruction *sourceInst = nullptr) {
-    return PartitionOp(PartitionOpKind::Assign, tgt, src, sourceInst);
+  static PartitionOp Assign(Element destElt, Element srcElt,
+                            Operand *srcOperand = nullptr) {
+    return PartitionOp(PartitionOpKind::Assign, destElt, srcElt, srcOperand);
   }
 
   static PartitionOp AssignFresh(Element tgt,
@@ -535,9 +543,10 @@ class PartitionOp {
     return PartitionOp(PartitionOpKind::UndoTransfer, tgt, untransferringInst);
   }
 
-  static PartitionOp Merge(Element tgt1, Element tgt2,
-                           SILInstruction *sourceInst = nullptr) {
-    return PartitionOp(PartitionOpKind::Merge, tgt1, tgt2, sourceInst);
+  static PartitionOp Merge(Element destElement, Element srcElement,
+                           Operand *sourceOperand = nullptr) {
+    return PartitionOp(PartitionOpKind::Merge, destElement, srcElement,
+                       sourceOperand);
   }
 
   static PartitionOp Require(Element tgt,