Utils: Add utility pass to lower ifuncs

Create a global constructor which will initialize a global table of
function pointers. For now, this is only used as a reduction technique
for llvm-reduce.

In the future this may be useful to support ifunc on systems where the
program loader doesn't natively support it.

1 files changed, 27 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/LowerIFunc.cpp b/llvm/lib/Transforms/Utils/LowerIFunc.cpp
new file mode 100644
index 0000000..18ae0bbe
--- /dev/null
+++ b/llvm/lib/Transforms/Utils/LowerIFunc.cpp
@@ -0,0 +1,27 @@
+//===- LowerIFunc.cpp -----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements replacing calls to ifuncs by introducing indirect calls.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/LowerIFunc.h"
+#include "llvm/IR/Module.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Utils/ModuleUtils.h"
+
+using namespace llvm;
+
+/// Replace all call users of ifuncs in the module.
+PreservedAnalyses LowerIFuncPass::run(Module &M, ModuleAnalysisManager &AM) {
+  if (M.ifunc_empty())
+    return PreservedAnalyses::all();
+
+  lowerGlobalIFuncUsersAsGlobalCtor(M, {});
+  return PreservedAnalyses::none();
+}