Add a new Jump Threading pass, which will handle cases
such as those in PR2235. Right now the pass is not very
effective. :)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50000 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
new file mode 100644
index 0000000..7773edb
--- /dev/null
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -0,0 +1,52 @@
+//===- JumpThreading.cpp - Thread control through conditional blocks ------===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs 'jump threading', which looks at blocks that have multiple
+// predecessors and multiple successors. If one or more of the predecessors of
+// the block can be proven to always jump to one of the successors, we forward
+// the edge from the predecessor to the successor by duplicating the contents of
+// this block.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "jump-threading"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Compiler.h"
+using namespace llvm;
+
+//STATISTIC(NumThreads, "Number of jumps threaded");
+
+namespace {
+ cl::opt<unsigned>
+ Threshold("jump-threading-threshold",
+ cl::desc("Max block size to duplicate for jump threading"),
+ cl::init(6), cl::Hidden);
+ class VISIBILITY_HIDDEN JumpThreading : public FunctionPass {
+ public:
+ static char ID; // Pass identification
+ JumpThreading() : FunctionPass((intptr_t)&ID) {}
+
+ bool runOnFunction(Function &F);
+ };
+ char JumpThreading::ID = 0;
+ RegisterPass<JumpThreading> X("jump-threading", "Jump Threading");
+}
+
+// Public interface to the Jump Threading pass
+FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); }
+
+/// runOnFunction - Top level algorithm.
+///
+bool JumpThreading::runOnFunction(Function &F) {
+ bool Changed = false;
+ return Changed;
+}