llvm-dg: preserve dbg intrinsic

We usually want them in the sliced code.

Part of a fix for staticafi/symbiotic#202

Author: mchalupa

include/dg/llvm/LLVMDependenceGraph.h

@@ -147,7 +147,7 @@ class LLVMDependenceGraph : public DependenceGraph<LLVMNode> {
 
     LLVMNode *findNode(llvm::Value *value) const;
 
-    void addDefUseEdges();
+    void addDefUseEdges(bool preserveDbg = true);
     void computeInterferenceDependentEdges(ControlFlowGraph *controlFlowGraph);
     static void computeForkJoinDependencies(ControlFlowGraph *controlFlowGraph);
     static void computeCriticalSections(ControlFlowGraph *controlFlowGraph);

include/dg/llvm/LLVMDependenceGraphBuilder.h

@@ -40,6 +40,7 @@ struct LLVMDependenceGraphOptions {
 
     bool verifyGraph{true};
     bool threads{false};
+    bool preserveDbg{true};
 
     std::string entryFunction{"main"};
 
@@ -164,7 +165,7 @@ class LLVMDependenceGraphBuilder {
         _dg->build(_M, _PTA.get(), _DDA.get(), _entryFunction);
 
         // insert the data dependencies edges
-        _dg->addDefUseEdges();
+        _dg->addDefUseEdges(_options.preserveDbg);
 
         // compute and fill-in control dependencies
         _runControlDependenceAnalysis();
@@ -228,7 +229,7 @@ class LLVMDependenceGraphBuilder {
 
         // data-dependence edges
         _runDataDependenceAnalysis();
-        _dg->addDefUseEdges();
+        _dg->addDefUseEdges(_options.preserveDbg);
 
         // fill-in control dependencies
         _runControlDependenceAnalysis();

lib/llvm/LLVMDependenceGraph.cpp

@@ -21,6 +21,7 @@
 #include <llvm/IR/DataLayout.h>
 #include <llvm/IR/Function.h>
 #include <llvm/IR/Instructions.h>
+#include <llvm/IR/InstIterator.h>
 #include <llvm/IR/Module.h>
 #include <llvm/IR/Value.h>
 #include <llvm/Support/raw_ostream.h>
@@ -1250,9 +1251,37 @@ void LLVMDependenceGraph::addNoreturnDependencies(
     }
 }
 
-void LLVMDependenceGraph::addDefUseEdges() {
+void LLVMDependenceGraph::addDefUseEdges(bool preserveDbg) {
     LLVMDefUseAnalysis DUA(this, DDA, PTA);
     DUA.run();
+
+    if (preserveDbg) {
+        using namespace llvm;
+
+        for (const auto &it : getConstructedFunctions()) {
+            LLVMDependenceGraph *dg = it.second;
+            for (auto &I : instructions(cast<Function>(it.first))) {
+                Value *val = nullptr;
+                if (auto *DI = dyn_cast<DbgDeclareInst>(&I))
+                    val = DI->getAddress();
+                else if (auto *DI = dyn_cast<DbgValueInst>(&I))
+                    val = DI->getValue();
+                else if (auto *DI = dyn_cast<DbgAddrIntrinsic>(&I))
+                    val = DI->getAddress();
+
+                if (val) {
+                    auto *nd = dg->getNode(&I);
+                    auto *ndop = dg->getNode(val);
+                    assert(nd && "Do not have a node for a dbg intrinsic");
+                    assert(ndop && "Do not have a node for an operand of a dbg intrinsic");
+                    // add a use edge such that we preserve
+                    // the debugging intrinsic when we preserve
+                    // the value it is talking about
+                    nd->addUseDependence(ndop);
+                }
+            }
+        }
+    }
 }
 
 LLVMNode *findInstruction(llvm::Instruction *instruction,

tools/llvm-slicer-opts.cpp

@@ -209,6 +209,11 @@ SlicerOptions parseSlicerOptions(int argc, char *argv[], bool requireCrit,
                     "Consider threads are in input file (default=false)."),
             llvm::cl::init(false), llvm::cl::cat(SlicingOpts));
 
+    llvm::cl::opt<bool> preserveDbg(
+            "preserve-dbg",
+            llvm::cl::desc("Preserve debugging information (default=true)."),
+            llvm::cl::init(true), llvm::cl::cat(SlicingOpts));
+
     llvm::cl::opt<std::string> allocationFuns(
             "allocation-funs",
             llvm::cl::desc(
@@ -380,6 +385,7 @@ SlicerOptions parseSlicerOptions(int argc, char *argv[], bool requireCrit,
     auto &CDAOptions = dgOptions.CDAOptions;
 
     dgOptions.entryFunction = entryFunction;
+    dgOptions.preserveDbg = preserveDbg;
     dgOptions.threads = threads;
 
     CDAOptions.algorithm = cdAlgorithm;