vendor/llvm/llvm-trunk-r301939

1 files changed, 53 insertions, 0 deletions

diff --git a/include/llvm/Transforms/Scalar/SimpleLoopUnswitch.h b/include/llvm/Transforms/Scalar/SimpleLoopUnswitch.h
new file mode 100644
index 000000000000..d7282ac6a781
--- /dev/null
+++ b/include/llvm/Transforms/Scalar/SimpleLoopUnswitch.h
@@ -0,0 +1,53 @@
+//===- SimpleLoopUnswitch.h - Hoist loop-invariant control flow -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TRANSFORMS_SCALAR_SIMPLELOOPUNSWITCH_H
+#define LLVM_TRANSFORMS_SCALAR_SIMPLELOOPUNSWITCH_H
+
+#include "llvm/Analysis/LoopAnalysisManager.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/Transforms/Scalar/LoopPassManager.h"
+
+namespace llvm {
+
+/// This pass transforms loops that contain branches on loop-invariant
+/// conditions to have multiple loops. For example, it turns the left into the
+/// right code:
+///
+///  for (...)                  if (lic)
+///    A                          for (...)
+///    if (lic)                     A; B; C
+///      B                      else
+///    C                          for (...)
+///                                 A; C
+///
+/// This can increase the size of the code exponentially (doubling it every time
+/// a loop is unswitched) so we only unswitch if the resultant code will be
+/// smaller than a threshold.
+///
+/// This pass expects LICM to be run before it to hoist invariant conditions out
+/// of the loop, to make the unswitching opportunity obvious.
+///
+class SimpleLoopUnswitchPass : public PassInfoMixin<SimpleLoopUnswitchPass> {
+public:
+  SimpleLoopUnswitchPass() = default;
+
+  PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
+                        LoopStandardAnalysisResults &AR, LPMUpdater &U);
+};
+
+/// Create the legacy pass object for the simple loop unswitcher.
+///
+/// See the documentaion for `SimpleLoopUnswitchPass` for details.
+Pass *createSimpleLoopUnswitchLegacyPass();
+
+} // end namespace llvm
+
+#endif // LLVM_TRANSFORMS_SCALAR_SIMPLELOOPUNSWITCH_H