[ConstraintElimination] Change debug output to display variable names.

Previously when constraint system outputs the rows in the system the variables used are x1,2...n making it hard to infer which ones they relate to in the IR

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D142618

llvm/include/llvm/Analysis/ConstraintSystem.h

@@ -36,13 +36,17 @@ class ConstraintSystem {
   // Eliminate constraints from the system using Fourier–Motzkin elimination.
   bool eliminateUsingFM();
 
-  /// Print the constraints in the system, using x0...xn as variable names.
-  void dump() const;
-
   /// Returns true if there may be a solution for the constraints in the system.
   bool mayHaveSolutionImpl();
 
+  /// Get list of variable names from the Value2Index map.
+  SmallVector<std::string> getVarNamesList() const;
+
 public:
+  ConstraintSystem() {}
+  ConstraintSystem(const DenseMap<Value *, unsigned> &Value2Index)
+      : Value2Index(Value2Index) {}
+
   bool addVariableRow(ArrayRef<int64_t> R) {
     assert(Constraints.empty() || R.size() == Constraints.back().size());
     // If all variable coefficients are 0, the constraint does not provide any
@@ -103,8 +107,8 @@ class ConstraintSystem {
   /// Returns the number of rows in the constraint system.
   unsigned size() const { return Constraints.size(); }
 
-  /// Print the constraints in the system, using \p Names as variable names.
-  void dump(ArrayRef<std::string> Names) const;
+  /// Print the constraints in the system.
+  void dump() const;
 };
 } // namespace llvm
 

llvm/lib/Analysis/ConstraintSystem.cpp

@@ -111,10 +111,23 @@ bool ConstraintSystem::mayHaveSolutionImpl() {
   return all_of(Constraints, [](auto &R) { return R[0] >= 0; });
 }
 
-void ConstraintSystem::dump(ArrayRef<std::string> Names) const {
+SmallVector<std::string> ConstraintSystem::getVarNamesList() const {
+  SmallVector<std::string> Names(Value2Index.size(), "");
+  for (auto &[V, Index] : Value2Index) {
+    std::string OperandName;
+    if (V->getName().empty())
+      OperandName = V->getNameOrAsOperand();
+    else
+      OperandName = std::string("%") + V->getName().str();
+    Names[Index - 1] = OperandName;
+  }
+  return Names;
+}
+
+void ConstraintSystem::dump() const {
   if (Constraints.empty())
     return;
-
+  SmallVector<std::string> Names = getVarNamesList();
   for (const auto &Row : Constraints) {
     SmallVector<std::string, 16> Parts;
     for (unsigned I = 1, S = Row.size(); I < S; ++I) {
@@ -131,14 +144,6 @@ void ConstraintSystem::dump(ArrayRef<std::string> Names) const {
   }
 }
 
-void ConstraintSystem::dump() const {
-  SmallVector<std::string, 16> Names;
-  for (unsigned i = 1; i < Constraints.back().size(); ++i)
-    Names.push_back("x" + std::to_string(i));
-  LLVM_DEBUG(dbgs() << "---\n");
-  dump(Names);
-}
-
 bool ConstraintSystem::mayHaveSolution() {
   LLVM_DEBUG(dump());
   bool HasSolution = mayHaveSolutionImpl();

llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

@@ -644,20 +644,12 @@ struct State {
 } // namespace
 
 #ifndef NDEBUG
-static void dumpWithNames(const ConstraintSystem &CS,
-                          DenseMap<Value *, unsigned> &Value2Index) {
-  SmallVector<std::string> Names(Value2Index.size(), "");
-  for (auto &KV : Value2Index) {
-    Names[KV.second - 1] = std::string("%") + KV.first->getName().str();
-  }
-  CS.dump(Names);
-}
 
-static void dumpWithNames(ArrayRef<int64_t> C,
-                          DenseMap<Value *, unsigned> &Value2Index) {
-  ConstraintSystem CS;
+static void dumpConstraint(ArrayRef<int64_t> C,
+                           const DenseMap<Value *, unsigned> &Value2Index) {
+  ConstraintSystem CS(Value2Index);
   CS.addVariableRowFill(C);
-  dumpWithNames(CS, Value2Index);
+  CS.dump();
 }
 #endif
 
@@ -1005,7 +997,7 @@ void ConstraintInfo::addFact(CmpInst::Predicate Pred, Value *A, Value *B,
 
     LLVM_DEBUG({
       dbgs() << "  constraint: ";
-      dumpWithNames(R.Coefficients, getValue2Index(R.IsSigned));
+      dumpConstraint(R.Coefficients, getValue2Index(R.IsSigned));
       dbgs() << "\n";
     });
 
@@ -1150,8 +1142,8 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT,
         break;
       LLVM_DEBUG({
         dbgs() << "Removing ";
-        dumpWithNames(Info.getCS(E.IsSigned).getLastConstraint(),
-                      Info.getValue2Index(E.IsSigned));
+        dumpConstraint(Info.getCS(E.IsSigned).getLastConstraint(),
+                       Info.getValue2Index(E.IsSigned));
         dbgs() << "\n";
       });