[libc] Extend WrapperGen to emit aliases.

Reviewed By: michaelrj

Differential Revision: https://reviews.llvm.org/D90985

libc/utils/tools/WrapperGen/Main.cpp

@@ -10,6 +10,7 @@
 
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/MemoryBuffer.h"
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Main.h"
 
@@ -19,8 +20,37 @@
 llvm::cl::opt<std::string>
     FunctionName("name", llvm::cl::desc("Name of the function to be wrapped."),
                  llvm::cl::value_desc("<function name>"), llvm::cl::Required);
+llvm::cl::opt<std::string>
+    AliaseeString("aliasee",
+                  llvm::cl::desc("Declare as an alias to this C name."),
+                  llvm::cl::value_desc("<aliasee string>"));
+llvm::cl::opt<std::string>
+    AliaseeFile("aliasee-file",
+                llvm::cl::desc("Declare as an alias to the C name read from "
+                               "this file."),
+                llvm::cl::value_desc("<path to a file containing alias name>"));
+llvm::cl::opt<std::string>
+    AppendToFile("append-to-file",
+                 llvm::cl::desc("Append the generated content at the end of "
+                                "the contents of this file."),
+                 llvm::cl::value_desc("<path to a file>"));
+
+static std::string GetAliaseeName() {
+  if (AliaseeString.size() > 0)
+    return AliaseeString;
+
+  auto ErrorOrBuf = llvm::MemoryBuffer::getFile(AliaseeFile);
+  if (!ErrorOrBuf)
+    llvm::PrintFatalError("Unable to read the aliasee file " + AliaseeFile);
+  return std::string(ErrorOrBuf.get()->getBuffer().trim());
+}
 
 static bool WrapperGenMain(llvm::raw_ostream &OS, llvm::RecordKeeper &Records) {
+  if (!AliaseeString.empty() && !AliaseeFile.empty()) {
+    llvm::PrintFatalError("The options 'aliasee' and 'aliasee-file' cannot "
+                          "be specified simultaniously.");
+  }
+
   llvm_libc::APIIndexer Indexer(Records);
   auto Iter = Indexer.FunctionSpecMap.find(FunctionName);
   if (Iter == Indexer.FunctionSpecMap.end()) {
@@ -28,11 +58,27 @@ static bool WrapperGenMain(llvm::raw_ostream &OS, llvm::RecordKeeper &Records) {
                           "' not found in any standard spec.");
   }
 
-  // To avoid all confusion, we include the implementation header using the
-  // full path (relative the libc directory.)
-  std::string Header = Indexer.FunctionToHeaderMap[FunctionName];
-  auto RelPath = llvm::StringRef(Header).drop_back(2); // Drop the ".h" suffix.
-  OS << "#include \"src/" << RelPath << "/" << FunctionName << ".h\"\n";
+  bool EmitAlias = !(AliaseeString.empty() && AliaseeFile.empty());
+
+  if (!EmitAlias && AppendToFile.empty()) {
+    // If not emitting an alias, and not appending to another file,
+    // we should include the implementation header to ensure the wrapper
+    // compiles.
+    // To avoid all confusion, we include the implementation header using the
+    // full path (relative to the libc directory.)
+    std::string Header = Indexer.FunctionToHeaderMap[FunctionName];
+    auto RelPath =
+        llvm::StringRef(Header).drop_back(2); // Drop the ".h" suffix.
+    OS << "#include \"src/" << RelPath << "/" << FunctionName << ".h\"\n";
+  }
+  if (!AppendToFile.empty()) {
+    auto ErrorOrBuf = llvm::MemoryBuffer::getFile(AppendToFile);
+    if (!ErrorOrBuf) {
+      llvm::PrintFatalError("Unable to read the file '" + AppendToFile +
+                            "' to append to.");
+    }
+    OS << ErrorOrBuf.get()->getBuffer().trim() << '\n';
+  }
 
   auto &NameSpecPair = *Iter;
   llvm::Record *FunctionSpec = NameSpecPair.second;
@@ -79,14 +125,17 @@ static bool WrapperGenMain(llvm::raw_ostream &OS, llvm::RecordKeeper &Records) {
     }
   }
 
-  // TODO: Arg types of the C++ implementation functions need not
-  // match the standard types. Either handle such differences here, or
-  // avoid such a thing in the implementations.
-  OS << ") {\n"
-     << "  " << (ShouldReturn ? "return " : "")
-     << "__llvm_libc::" << FunctionName << "(" << CallArgs.str() << ");\n"
-     << "}\n";
-
+  if (EmitAlias) {
+    OS << ") __attribute__((alias(\"" << GetAliaseeName() << "\")));\n";
+  } else {
+    // TODO: Arg types of the C++ implementation functions need not
+    // match the standard types. Either handle such differences here, or
+    // avoid such a thing in the implementations.
+    OS << ") {\n"
+       << "  " << (ShouldReturn ? "return " : "")
+       << "__llvm_libc::" << FunctionName << "(" << CallArgs.str() << ");\n"
+       << "}\n";
+  }
   return false;
 }