[clang] [CIR] Upstream a basic version of class LexicalScope (PR #131945)

[Erich Keane via cfe-commits]

================
@@ -149,14 +156,125 @@ void CIRGenFunction::declare(mlir::Value addrVal, const Decl *var, QualType ty,
     allocaOp.setConstantAttr(mlir::UnitAttr::get(&getMLIRContext()));
 }
 
+void CIRGenFunction::LexicalScope::cleanup() {
+  CIRGenBuilderTy &builder = cgf.builder;
+  LexicalScope *localScope = cgf.currLexScope;
+
+  if (returnBlock != nullptr) {
+    // Write out the return block, which loads the value from `__retval` and
+    // issues the `cir.return`.
+    mlir::OpBuilder::InsertionGuard guard(builder);
+    builder.setInsertionPointToEnd(returnBlock);
+    (void)emitReturn(*returnLoc);
+  }
+
+  mlir::Block *currBlock = builder.getBlock();
+  if (isGlobalInit() && !currBlock)
+    return;
+  if (currBlock->mightHaveTerminator() && currBlock->getTerminator())
+    return;
+
+  // Get rid of any empty block at the end of the scope.
+  bool entryBlock = builder.getInsertionBlock()->isEntryBlock();
+  if (!entryBlock && currBlock->empty()) {
+    currBlock->erase();
+    if (returnBlock != nullptr && returnBlock->getUses().empty())
+      returnBlock->erase();
+    return;
+  }
+
+  // Reached the end of the scope.
+  {
+    mlir::OpBuilder::InsertionGuard guard(builder);
+    builder.setInsertionPointToEnd(currBlock);
+
+    if (localScope->depth == 0) {
+      // Reached the end of the function.
+      if (returnBlock != nullptr) {
+        if (returnBlock->getUses().empty())
+          returnBlock->erase();
+        else {
+          builder.create<cir::BrOp>(*returnLoc, returnBlock);
+          return;
+        }
+      }
+      emitImplicitReturn();
+      return;
+    }
+    // Reached the end of a non-function scope.  Some scopes, such as those
+    // used with the ?: operator, can return a value.
+    if (!localScope->isTernary() && !currBlock->mightHaveTerminator()) {
+      !retVal ? builder.create<cir::YieldOp>(localScope->endLoc)
+              : builder.create<cir::YieldOp>(localScope->endLoc, retVal);
+    }
+  }
+}
+
+cir::ReturnOp CIRGenFunction::LexicalScope::emitReturn(mlir::Location loc) {
+  CIRGenBuilderTy &builder = cgf.getBuilder();
+
+  if (!cgf.curFn.getFunctionType().hasVoidReturn()) {
+    // Load the value from `__retval` and return it via the `cir.return` op.
+    auto value = builder.create<cir::LoadOp>(
+        loc, cgf.curFn.getFunctionType().getReturnType(), *cgf.fnRetAlloca);
+    return builder.create<cir::ReturnOp>(loc,
+                                         llvm::ArrayRef(value.getResult()));
+  }
+  return builder.create<cir::ReturnOp>(loc);
+}
+
+// This is copyied from CodeGenModule::MayDropFunctionReturn.  This is a
----------------
erichkeane wrote:

```suggestion
// This is copied from CodeGenModule::MayDropFunctionReturn.  This is a
```

https://github.com/llvm/llvm-project/pull/131945