[DA] GPUDivergenceAnalysis for unstructured GPU kernels

Summary:
This is patch #3 of the new DivergenceAnalysis

  <https://lists.llvm.org/pipermail/llvm-dev/2018-May/123606.html>

The GPUDivergenceAnalysis is intended to eventually supersede the existing
LegacyDivergenceAnalysis. The existing LegacyDivergenceAnalysis produces
incorrect results on unstructured Control-Flow Graphs:

  <https://bugs.llvm.org/show_bug.cgi?id=37185>

This patch adds the option -use-gpu-divergence-analysis to the
LegacyDivergenceAnalysis to turn it into a transparent wrapper for the
GPUDivergenceAnalysis.

Reviewers: nhaehnle

Reviewed By: nhaehnle

Subscribers: jholewinski, jvesely, jfb, llvm-commits, alex-t, sameerds, arsenm, nhaehnle

Differential Revision: https://reviews.llvm.org/D53493

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@348048 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/DivergenceAnalysis.cpp

@@ -422,3 +422,36 @@ void DivergenceAnalysis::print(raw_ostream &OS, const Module *) const {
       OS << "DIVERGENT:" << I << '\n';
   }
 }
+
+// class GPUDivergenceAnalysis
+GPUDivergenceAnalysis::GPUDivergenceAnalysis(Function &F,
+                                             const DominatorTree &DT,
+                                             const PostDominatorTree &PDT,
+                                             const LoopInfo &LI,
+                                             const TargetTransformInfo &TTI)
+    : SDA(DT, PDT, LI), DA(F, nullptr, DT, LI, SDA, false) {
+  for (auto &I : instructions(F)) {
+    if (TTI.isSourceOfDivergence(&I)) {
+      DA.markDivergent(I);
+    } else if (TTI.isAlwaysUniform(&I)) {
+      DA.addUniformOverride(I);
+    }
+  }
+  for (auto &Arg : F.args()) {
+    if (TTI.isSourceOfDivergence(&Arg)) {
+      DA.markDivergent(Arg);
+    }
+  }
+
+  DA.compute();
+}
+
+bool GPUDivergenceAnalysis::isDivergent(const Value &val) const {
+  return DA.isDivergent(val);
+}
+
+void GPUDivergenceAnalysis::print(raw_ostream &OS, const Module *mod) const {
+  OS << "Divergence of kernel " << DA.getFunction().getName() << " {\n";
+  DA.print(OS, mod);
+  OS << "}\n";
+}