Add a speculative execution pass

Summary:
This is a pass for speculative execution of instructions for simple if-then (triangle) control flow. It's aimed at GPUs, but could perhaps be used in other contexts. Enabling this pass gives us a 1.0% geomean improvement on Google benchmark suites, with one benchmark improving 33%.

Credit goes to Jingyue Wu for writing an earlier version of this pass.

Patched by Bjarke Roune. 

Test Plan:
This patch adds a set of tests in test/Transforms/SpeculativeExecution/spec.ll
The pass is controlled by a flag which defaults to having the pass not run.

Reviewers: eliben, dberlin, meheff, jingyue, hfinkel

Reviewed By: jingyue, hfinkel

Subscribers: majnemer, jholewinski, llvm-commits

Differential Revision: http://reviews.llvm.org/D9360

llvm-svn: 237459

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/IR/BasicBlock.cpp b/llvm/lib/IR/BasicBlock.cpp
index 23ec7052954..e6a4585a936 100644
--- a/llvm/lib/IR/BasicBlock.cpp
+++ b/llvm/lib/IR/BasicBlock.cpp
@@ -238,6 +238,14 @@ BasicBlock *BasicBlock::getUniquePredecessor() {
   return PredBB;
 }
 
+BasicBlock *BasicBlock::getSingleSuccessor() {
+  succ_iterator SI = succ_begin(this), E = succ_end(this);
+  if (SI == E) return nullptr; // no successors
+  BasicBlock *TheSucc = *SI;
+  ++SI;
+  return (SI == E) ? TheSucc : nullptr /* multiple successors */;
+}
+
 BasicBlock *BasicBlock::getUniqueSuccessor() {
   succ_iterator SI = succ_begin(this), E = succ_end(this);
   if (SI == E) return NULL; // No successors