[llvm] a78ce48 - [ConstraintElimination] Introduce struct to manage constraints. (NFC)

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2022-01-27T12:40:09Z
New Revision: a78ce48c373572946a51228dda741681d1695d63

URL: https://github.com/llvm/llvm-project/commit/a78ce48c373572946a51228dda741681d1695d63
DIFF: https://github.com/llvm/llvm-project/commit/a78ce48c373572946a51228dda741681d1695d63.diff

LOG: [ConstraintElimination] Introduce struct to manage constraints. (NFC)

This patch adds a struct to manage a list of constraints. It simplifies
a follow-up change, that adds pre-conditions that must hold before a
list of constraints can be used.

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/ConstraintElimination.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index fcb88b54a094..0c4d7c8ecb48 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -43,6 +43,51 @@ DEBUG_COUNTER(EliminatedCounter, "conds-eliminated",
 
 static int64_t MaxConstraintValue = std::numeric_limits<int64_t>::max();
 
+namespace {
+struct ConstraintTy {
+  SmallVector<int64_t, 8> Coefficients;
+
+  ConstraintTy(SmallVector<int64_t, 8> Coefficients)
+      : Coefficients(Coefficients) {}
+
+  unsigned size() const { return Coefficients.size(); }
+};
+
+/// Struct to manage a list of constraints.
+struct ConstraintListTy {
+  SmallVector<ConstraintTy, 4> Constraints;
+
+  ConstraintListTy() {}
+
+  ConstraintListTy(const SmallVector<ConstraintTy, 4> &Constraints)
+      : Constraints(Constraints) {}
+
+  void mergeIn(const ConstraintListTy &Other) {
+    append_range(Constraints, Other.Constraints);
+  }
+
+  unsigned size() const { return Constraints.size(); }
+
+  unsigned empty() const { return Constraints.empty(); }
+
+  /// Returns true if any constraint has a non-zero coefficient for any of the
+  /// newly added indices. Zero coefficients for new indices are removed. If it
+  /// returns true, no new variable need to be added to the system.
+  bool needsNewIndices(const DenseMap<Value *, unsigned> &NewIndices) {
+    assert(size() == 1);
+    for (unsigned I = 0; I < NewIndices.size(); ++I) {
+      int64_t Last = get(0).Coefficients.pop_back_val();
+      if (Last != 0)
+        return true;
+    }
+    return false;
+  }
+
+  ConstraintTy &get(unsigned I) { return Constraints[I]; }
+};
+
+} // namespace
+
 // Decomposes \p V into a vector of pairs of the form { c, X } where c * X. The
 // sum of the pairs equals \p V.  The first pair is the constant-factor and X
 // must be nullptr. If the expression cannot be decomposed, returns an empty
@@ -113,19 +158,10 @@ static SmallVector<std::pair<int64_t, Value *>, 4> decompose(Value *V) {
   return {{0, nullptr}, {1, V}};
 }
 
-struct ConstraintTy {
-  SmallVector<int64_t, 8> Coefficients;
-
-  ConstraintTy(SmallVector<int64_t, 8> Coefficients)
-      : Coefficients(Coefficients) {}
-
-  unsigned size() const { return Coefficients.size(); }
-};
-
 /// Turn a condition \p CmpI into a vector of constraints, using indices from \p
 /// Value2Index. Additional indices for newly discovered values are added to \p
 /// NewIndices.
-static SmallVector<ConstraintTy, 4>
+static ConstraintListTy
 getConstraint(CmpInst::Predicate Pred, Value *Op0, Value *Op1,
               const DenseMap<Value *, unsigned> &Value2Index,
               DenseMap<Value *, unsigned> &NewIndices) {
@@ -155,7 +191,7 @@ getConstraint(CmpInst::Predicate Pred, Value *Op0, Value *Op1,
         getConstraint(CmpInst::ICMP_UGE, Op0, Op1, Value2Index, NewIndices);
     auto B =
         getConstraint(CmpInst::ICMP_ULE, Op0, Op1, Value2Index, NewIndices);
-    append_range(A, B);
+    A.mergeIn(B);
     return A;
   }
 
@@ -200,10 +236,10 @@ getConstraint(CmpInst::Predicate Pred, Value *Op0, Value *Op1,
     R[GetOrAddIndex(KV.second)] -= KV.first;
 
   R[0] = Offset1 + Offset2 + (Pred == CmpInst::ICMP_ULT ? -1 : 0);
-  return {R};
+  return {{R}};
 }
 
-static SmallVector<ConstraintTy, 4>
+static ConstraintListTy
 getConstraint(CmpInst *Cmp, const DenseMap<Value *, unsigned> &Value2Index,
               DenseMap<Value *, unsigned> &NewIndices) {
   return getConstraint(Cmp->getPredicate(), Cmp->getOperand(0),
@@ -397,21 +433,10 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT) {
         if (R.size() != 1)
           continue;
 
-        // Check if all coefficients of new indices are 0 after building the
-        // constraint. Skip if any of the new indices has a non-null
-        // coefficient.
-        bool HasNewIndex = false;
-        for (unsigned I = 0; I < NewIndices.size(); ++I) {
-          int64_t Last = R[0].Coefficients.pop_back_val();
-          if (Last != 0) {
-            HasNewIndex = true;
-            break;
-          }
-        }
-        if (HasNewIndex || R[0].size() == 1)
+        if (R.needsNewIndices(NewIndices) || R.get(0).size() == 1)
           continue;
 
-        if (CS.isConditionImplied(R[0].Coefficients)) {
+        if (CS.isConditionImplied(R.get(0).Coefficients)) {
           if (!DebugCounter::shouldExecute(EliminatedCounter))
             continue;
 
@@ -432,7 +457,7 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT) {
           Changed = true;
         }
         if (CS.isConditionImplied(
-                ConstraintSystem::negate(R[0].Coefficients))) {
+                ConstraintSystem::negate(R.get(0).Coefficients))) {
           if (!DebugCounter::shouldExecute(EliminatedCounter))
             continue;
 
@@ -479,7 +504,7 @@ static bool eliminateConstraints(Function &F, DominatorTree &DT) {
 
     LLVM_DEBUG(dbgs() << "Adding " << *CB.Condition << " " << CB.Not << "\n");
     bool Added = false;
-    for (auto &C : R) {
+    for (auto &C : R.Constraints) {
       auto Coeffs = C.Coefficients;
       LLVM_DEBUG({
         dbgs() << "  constraint: ";