[region-isolation] Create helpers for inferring name from value and infer name/root from value.

This just cleans up the code by not exposing the details from the
VariableNameInferrer outside of the utilities. It also makes it easier to write
conditional code that uses these helpers by returning an optional, so instead of
having a long setup + an if statement, we just have an if statement optional
check.

Author: gottesmm

lib/SILOptimizer/Mandatory/TransferNonSendable.cpp

@@ -88,6 +88,34 @@ static Expr *inferArgumentExprFromApplyExpr(ApplyExpr *sourceApply,
   return foundExpr;
 }
 
+static std::optional<Identifier> inferNameFromValue(SILValue value) {
+  auto *fn = value->getFunction();
+  if (!fn)
+    return {};
+  VariableNameInferrer::Options options;
+  options |= VariableNameInferrer::Flag::InferSelfThroughAllAccessors;
+  SmallString<64> resultingName;
+  VariableNameInferrer inferrer(fn, options, resultingName);
+  if (!inferrer.inferByWalkingUsesToDefsReturningRoot(value))
+    return {};
+  return fn->getASTContext().getIdentifier(resultingName);
+}
+
+static std::optional<std::pair<Identifier, SILValue>>
+inferNameAndRootFromValue(SILValue value) {
+  auto *fn = value->getFunction();
+  if (!fn)
+    return {};
+  VariableNameInferrer::Options options;
+  options |= VariableNameInferrer::Flag::InferSelfThroughAllAccessors;
+  SmallString<64> resultingName;
+  VariableNameInferrer inferrer(fn, options, resultingName);
+  SILValue rootValue = inferrer.inferByWalkingUsesToDefsReturningRoot(value);
+  if (!rootValue)
+    return {};
+  return {{fn->getASTContext().getIdentifier(resultingName), rootValue}};
+}
+
 //===----------------------------------------------------------------------===//
 //                             MARK: Diagnostics
 //===----------------------------------------------------------------------===//
@@ -748,25 +776,19 @@ void UseAfterTransferDiagnosticInferrer::init(const Operand *op) {
   if (auto *sourceApply = loc.getAsASTNode<ApplyExpr>()) {
     // Before we do anything further, see if we can find a name and emit a name
     // error.
-    SmallString<64> resultingName;
-    VariableNameInferrer::Options options;
-    options |= VariableNameInferrer::Flag::InferSelfThroughAllAccessors;
-    VariableNameInferrer inferrer(op->getFunction(), options, resultingName);
-    auto &astContext = op->getFunction()->getASTContext();
-    if (auto rootValue =
-            inferrer.inferByWalkingUsesToDefsReturningRoot(op->get())) {
-      if (auto *svi = dyn_cast<SingleValueInstruction>(rootValue)) {
+    if (auto rootValueAndName = inferNameAndRootFromValue(op->get())) {
+      if (auto *svi =
+              dyn_cast<SingleValueInstruction>(rootValueAndName->second)) {
         return appendUseInfo(UseDiagnosticInfo::forNamedIsolationCrossing(
-            baseLoc, svi->getLoc(),
-            astContext.getIdentifier(inferrer.getName()),
+            baseLoc, svi->getLoc(), rootValueAndName->first,
             *sourceApply->getIsolationCrossing()));
       }
 
-      if (auto *fArg = dyn_cast<SILFunctionArgument>(rootValue)) {
+      if (auto *fArg =
+              dyn_cast<SILFunctionArgument>(rootValueAndName->second)) {
         return appendUseInfo(UseDiagnosticInfo::forNamedIsolationCrossing(
             baseLoc, RegularLocation(fArg->getDecl()->getLoc()),
-            astContext.getIdentifier(inferrer.getName()),
-            *sourceApply->getIsolationCrossing()));
+            rootValueAndName->first, *sourceApply->getIsolationCrossing()));
       }
     }
 
@@ -1105,13 +1127,8 @@ bool TransferNonTransferrableDiagnosticInferrer::run() {
 
     // See if we can infer a name from the value.
     SmallString<64> resultingName;
-    VariableNameInferrer::Options options;
-    options |= VariableNameInferrer::Flag::InferSelfThroughAllAccessors;
-    VariableNameInferrer inferrer(op->getFunction(), options, resultingName);
-    if (inferrer.inferByWalkingUsesToDefsReturningRoot(op->get())) {
-      auto &astContext = op->getFunction()->getASTContext();
-      diagnosticInfo = UseDiagnosticInfo::forNamed(
-          astContext.getIdentifier(inferrer.getName()), *isolation);
+    if (auto name = inferNameFromValue(op->get())) {
+      diagnosticInfo = UseDiagnosticInfo::forNamed(*name, *isolation);
       return true;
     }