//
// This file implements the Jump Threading pass.
//
+// Jump threading tries to find distinct threads of control flow running through
+// a basic block. This pass 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 cause a jump to one of the successors, we forward the edge
+// from the predecessor to the successor by duplicating the contents of this
+// block.
+//
+// An example of when this can occur is code like this:
+//
+// if () { ...
+// X = 4;
+// }
+// if (X < 3) {
+//
+// In this case, the unconditional branch at the end of the first if can be
+// revectored to the false side of the second if.
+//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "jump-threading"
cl::init(6), cl::Hidden);
namespace {
- /// 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.
- ///
- /// An example of when this can occur is code like this:
- ///
- /// if () { ...
- /// X = 4;
- /// }
- /// if (X < 3) {
- ///
- /// In this case, the unconditional branch at the end of the first if can be
- /// revectored to the false side of the second if.
- ///
class VISIBILITY_HIDDEN JumpThreading : public FunctionPass {
public:
static char ID; // Pass identification