Simplify affine binary op expression class hierarchy

- Drop sub-classing of affine binary op expressions.
- Drop affine expr op kind sub. Represent it as multiply by -1 and add. This
  will also be in line with the math form when we'll need to represent a system of
  linear equalities/inequalities: the negative number goes into the coefficient
  of an affine form. (For eg. x_1 + (-1)*x_2 + 3*x_3 + (-2) >= 0). The folding
  simplification will transparently deal with multiplying the -1 with any other
  constants. This also means we won't need to simplify a multiply expression
  like in x_1 + (-2)*x_2 to a subtract expression (x_1 - 2*x_2) for
  canonicalization/uniquing.
- When we print the IR, we will still pretty print to a subtract when possible.

PiperOrigin-RevId: 205298958
diff --git a/lib/IR/AffineExpr.cpp b/lib/IR/AffineExpr.cpp
index 8d0ee3d..6bfbaf5 100644
--- a/lib/IR/AffineExpr.cpp
+++ b/lib/IR/AffineExpr.cpp
@@ -28,27 +28,19 @@
   switch (kind) {
   case Kind::Add:
     assert(!isa<AffineConstantExpr>(lhs));
-    // TODO (more verification)
-    break;
-  case Kind::Sub:
-    // TODO (verification)
     break;
   case Kind::Mul:
     assert(!isa<AffineConstantExpr>(lhs));
     assert(rhs->isSymbolicOrConstant());
-    // TODO (more verification)
     break;
   case Kind::FloorDiv:
     assert(rhs->isSymbolicOrConstant());
-    // TODO (more verification)
     break;
   case Kind::CeilDiv:
     assert(rhs->isSymbolicOrConstant());
-    // TODO (more verification)
     break;
   case Kind::Mod:
     assert(rhs->isSymbolicOrConstant());
-    // TODO (more verification)
     break;
   default:
     llvm_unreachable("unexpected binary affine expr");
@@ -67,7 +59,6 @@
     return true;
 
   case Kind::Add:
-  case Kind::Sub:
   case Kind::Mul:
   case Kind::FloorDiv:
   case Kind::CeilDiv:
@@ -87,16 +78,15 @@
   case Kind::DimId:
   case Kind::Constant:
     return true;
-  case Kind::Add:
-  case Kind::Sub: {
-    auto op = cast<AffineBinaryOpExpr>(this);
+  case Kind::Add: {
+    auto *op = cast<AffineBinaryOpExpr>(this);
     return op->getLHS()->isPureAffine() && op->getRHS()->isPureAffine();
   }
 
   case Kind::Mul: {
     // TODO: Canonicalize the constants in binary operators to the RHS when
     // possible, allowing this to merge into the next case.
-    auto op = cast<AffineBinaryOpExpr>(this);
+    auto *op = cast<AffineBinaryOpExpr>(this);
     return op->getLHS()->isPureAffine() && op->getRHS()->isPureAffine() &&
            (isa<AffineConstantExpr>(op->getLHS()) ||
             isa<AffineConstantExpr>(op->getRHS()));
@@ -104,7 +94,7 @@
   case Kind::FloorDiv:
   case Kind::CeilDiv:
   case Kind::Mod: {
-    auto op = cast<AffineBinaryOpExpr>(this);
+    auto *op = cast<AffineBinaryOpExpr>(this);
     return op->getLHS()->isPureAffine() &&
            isa<AffineConstantExpr>(op->getRHS());
   }
diff --git a/lib/IR/AffineMap.cpp b/lib/IR/AffineMap.cpp
index d8e09b5..8972510 100644
--- a/lib/IR/AffineMap.cpp
+++ b/lib/IR/AffineMap.cpp
@@ -38,7 +38,7 @@
 
   if (isa<AffineConstantExpr>(lhs) ||
       (lhs->isSymbolicOrConstant() && !rhs->isSymbolicOrConstant()))
-    return AffineAddExpr::get(rhs, lhs, context);
+    return AffineBinaryOpExpr::get(Kind::Add, rhs, lhs, context);
 
   return nullptr;
   // TODO(someone): implement more simplification like x + 0 -> x; (x + 2) + 4
@@ -46,16 +46,6 @@
   // simplifications as opposed to incremental hacks.
 }
 
-AffineExpr *AffineBinaryOpExpr::simplifySub(AffineExpr *lhs, AffineExpr *rhs,
-                                            MLIRContext *context) {
-  if (auto *l = dyn_cast<AffineConstantExpr>(lhs))
-    if (auto *r = dyn_cast<AffineConstantExpr>(rhs))
-      return AffineConstantExpr::get(l->getValue() - r->getValue(), context);
-
-  return nullptr;
-  // TODO(someone): implement more simplification like mentioned for add.
-}
-
 /// Simplify a multiply expression. Fold it to a constant when possible, and
 /// make the symbolic/constant operand the RHS.
 AffineExpr *AffineBinaryOpExpr::simplifyMul(AffineExpr *lhs, AffineExpr *rhs,
@@ -71,7 +61,7 @@
   // constant. (Note that a constant is trivially symbolic).
   if (!rhs->isSymbolicOrConstant() || isa<AffineConstantExpr>(lhs)) {
     // At least one of them has to be symbolic.
-    return AffineMulExpr::get(rhs, lhs, context);
+    return AffineBinaryOpExpr::get(Kind::Mul, rhs, lhs, context);
   }
 
   return nullptr;
diff --git a/lib/IR/AsmPrinter.cpp b/lib/IR/AsmPrinter.cpp
index 570ae49..03d9b1d 100644
--- a/lib/IR/AsmPrinter.cpp
+++ b/lib/IR/AsmPrinter.cpp
@@ -661,38 +661,62 @@
   llvm::errs() << "\n";
 }
 
-void AffineAddExpr::print(raw_ostream &os) const {
-  os << "(" << *getLHS() << " + " << *getRHS() << ")";
-}
-
-void AffineSubExpr::print(raw_ostream &os) const {
-  os << "(" << *getLHS() << " - " << *getRHS() << ")";
-}
-
-void AffineMulExpr::print(raw_ostream &os) const {
-  os << "(" << *getLHS() << " * " << *getRHS() << ")";
-}
-
-void AffineModExpr::print(raw_ostream &os) const {
-  os << "(" << *getLHS() << " mod " << *getRHS() << ")";
-}
-
-void AffineFloorDivExpr::print(raw_ostream &os) const {
-  os << "(" << *getLHS() << " floordiv " << *getRHS() << ")";
-}
-
-void AffineCeilDivExpr::print(raw_ostream &os) const {
-  os << "(" << *getLHS() << " ceildiv " << *getRHS() << ")";
-}
-
 void AffineSymbolExpr::print(raw_ostream &os) const {
-  os << "s" << getPosition();
+  os << 's' << getPosition();
 }
 
-void AffineDimExpr::print(raw_ostream &os) const { os << "d" << getPosition(); }
+void AffineDimExpr::print(raw_ostream &os) const { os << 'd' << getPosition(); }
 
 void AffineConstantExpr::print(raw_ostream &os) const { os << getValue(); }
 
+static void printAdd(const AffineBinaryOpExpr *addExpr, raw_ostream &os) {
+  os << '(' << *addExpr->getLHS();
+
+  // Pretty print addition to a product that has a negative operand as a
+  // subtraction.
+  if (auto *rhs = dyn_cast<AffineBinaryOpExpr>(addExpr->getRHS())) {
+    if (rhs->getKind() == AffineExpr::Kind::Mul) {
+      if (auto *rrhs = dyn_cast<AffineConstantExpr>(rhs->getRHS())) {
+        if (rrhs->getValue() < 0) {
+          os << " - (" << *rhs->getLHS() << " * " << -rrhs->getValue() << "))";
+          return;
+        }
+      }
+    }
+  }
+
+  // Pretty print addition to a negative number as a subtraction.
+  if (auto *rhs = dyn_cast<AffineConstantExpr>(addExpr->getRHS())) {
+    if (rhs->getValue() < 0) {
+      os << " - " << -rhs->getValue() << ")";
+      return;
+    }
+  }
+
+  os << " + " << *addExpr->getRHS() << ")";
+}
+
+void AffineBinaryOpExpr::print(raw_ostream &os) const {
+  switch (getKind()) {
+  case Kind::Add:
+    return printAdd(this, os);
+  case Kind::Mul:
+    os << "(" << *getLHS() << " * " << *getRHS() << ")";
+    return;
+  case Kind::FloorDiv:
+    os << "(" << *getLHS() << " floordiv " << *getRHS() << ")";
+    return;
+  case Kind::CeilDiv:
+    os << "(" << *getLHS() << " ceildiv " << *getRHS() << ")";
+    return;
+  case Kind::Mod:
+    os << "(" << *getLHS() << " mod " << *getRHS() << ")";
+    return;
+  default:
+    llvm_unreachable("unexpected affine binary op expression");
+  }
+}
+
 void AffineExpr::print(raw_ostream &os) const {
   switch (getKind()) {
   case Kind::SymbolId:
@@ -702,17 +726,11 @@
   case Kind::Constant:
     return cast<AffineConstantExpr>(this)->print(os);
   case Kind::Add:
-    return cast<AffineAddExpr>(this)->print(os);
-  case Kind::Sub:
-    return cast<AffineSubExpr>(this)->print(os);
   case Kind::Mul:
-    return cast<AffineMulExpr>(this)->print(os);
   case Kind::FloorDiv:
-    return cast<AffineFloorDivExpr>(this)->print(os);
   case Kind::CeilDiv:
-    return cast<AffineCeilDivExpr>(this)->print(os);
   case Kind::Mod:
-    return cast<AffineModExpr>(this)->print(os);
+    return cast<AffineBinaryOpExpr>(this)->print(os);
   }
 }
 
diff --git a/lib/IR/Builders.cpp b/lib/IR/Builders.cpp
index 3d7e023..dc5b8e2 100644
--- a/lib/IR/Builders.cpp
+++ b/lib/IR/Builders.cpp
@@ -121,27 +121,23 @@
 }
 
 AffineExpr *Builder::getAddExpr(AffineExpr *lhs, AffineExpr *rhs) {
-  return AffineAddExpr::get(lhs, rhs, context);
-}
-
-AffineExpr *Builder::getSubExpr(AffineExpr *lhs, AffineExpr *rhs) {
-  return AffineSubExpr::get(lhs, rhs, context);
+  return AffineBinaryOpExpr::get(AffineExpr::Kind::Add, lhs, rhs, context);
 }
 
 AffineExpr *Builder::getMulExpr(AffineExpr *lhs, AffineExpr *rhs) {
-  return AffineMulExpr::get(lhs, rhs, context);
+  return AffineBinaryOpExpr::get(AffineExpr::Kind::Mul, lhs, rhs, context);
 }
 
 AffineExpr *Builder::getModExpr(AffineExpr *lhs, AffineExpr *rhs) {
-  return AffineModExpr::get(lhs, rhs, context);
+  return AffineBinaryOpExpr::get(AffineExpr::Kind::Mod, lhs, rhs, context);
 }
 
 AffineExpr *Builder::getFloorDivExpr(AffineExpr *lhs, AffineExpr *rhs) {
-  return AffineFloorDivExpr::get(lhs, rhs, context);
+  return AffineBinaryOpExpr::get(AffineExpr::Kind::FloorDiv, lhs, rhs, context);
 }
 
 AffineExpr *Builder::getCeilDivExpr(AffineExpr *lhs, AffineExpr *rhs) {
-  return AffineCeilDivExpr::get(lhs, rhs, context);
+  return AffineBinaryOpExpr::get(AffineExpr::Kind::CeilDiv, lhs, rhs, context);
 }
 
 //===----------------------------------------------------------------------===//
diff --git a/lib/IR/MLIRContext.cpp b/lib/IR/MLIRContext.cpp
index df3d01a..8d2de10 100644
--- a/lib/IR/MLIRContext.cpp
+++ b/lib/IR/MLIRContext.cpp
@@ -684,9 +684,6 @@
   case Kind::Add:
     simplified = AffineBinaryOpExpr::simplifyAdd(lhs, rhs, context);
     break;
-  case Kind::Sub:
-    simplified = AffineBinaryOpExpr::simplifySub(lhs, rhs, context);
-    break;
   case Kind::Mul:
     simplified = AffineBinaryOpExpr::simplifyMul(lhs, rhs, context);
     break;
@@ -720,36 +717,6 @@
   return result;
 }
 
-AffineExpr *AffineAddExpr::get(AffineExpr *lhs, AffineExpr *rhs,
-                               MLIRContext *context) {
-  return AffineBinaryOpExpr::get(Kind::Add, lhs, rhs, context);
-}
-
-AffineExpr *AffineSubExpr::get(AffineExpr *lhs, AffineExpr *rhs,
-                               MLIRContext *context) {
-  return AffineBinaryOpExpr::get(Kind::Sub, lhs, rhs, context);
-}
-
-AffineExpr *AffineMulExpr::get(AffineExpr *lhs, AffineExpr *rhs,
-                               MLIRContext *context) {
-  return AffineBinaryOpExpr::get(Kind::Mul, lhs, rhs, context);
-}
-
-AffineExpr *AffineFloorDivExpr::get(AffineExpr *lhs, AffineExpr *rhs,
-                                    MLIRContext *context) {
-  return AffineBinaryOpExpr::get(Kind::FloorDiv, lhs, rhs, context);
-}
-
-AffineExpr *AffineCeilDivExpr::get(AffineExpr *lhs, AffineExpr *rhs,
-                                   MLIRContext *context) {
-  return AffineBinaryOpExpr::get(Kind::CeilDiv, lhs, rhs, context);
-}
-
-AffineExpr *AffineModExpr::get(AffineExpr *lhs, AffineExpr *rhs,
-                               MLIRContext *context) {
-  return AffineBinaryOpExpr::get(Kind::Mod, lhs, rhs, context);
-}
-
 AffineDimExpr *AffineDimExpr::get(unsigned position, MLIRContext *context) {
   // TODO(bondhugula): complete this
   // FIXME: this should be POD