[mlir] Don't assert when simplifying certain AffineExprs (#78855)

Currently, `simplifyMul()` asserts that either `lhs` or `rhs` is
symbolic or constant. This method is called by the overloaded `*`
operator for `AffineExpr`s which leads to a crash when building a
multiplication expression where neither operand is symbolic or constant.
This patch returns a `nullptr` from `simplifyMul()` to signal that the
expression could not be simplified instead.

Fix #75770

Author: ubfx

mlir/lib/IR/AffineExpr.cpp

@@ -774,7 +774,8 @@ static AffineExpr simplifyMul(AffineExpr lhs, AffineExpr rhs) {
     return getAffineConstantExpr(lhsConst.getValue() * rhsConst.getValue(),
                                  lhs.getContext());
 
-  assert(lhs.isSymbolicOrConstant() || rhs.isSymbolicOrConstant());
+  if (!lhs.isSymbolicOrConstant() && !rhs.isSymbolicOrConstant())
+    return nullptr;
 
   // Canonicalize the mul expression so that the constant/symbolic term is the
   // RHS. If both the lhs and rhs are symbolic, swap them if the lhs is a

mlir/unittests/IR/AffineExprTest.cpp

@@ -0,0 +1,32 @@
+//===- AffineExprTest.cpp - unit tests for affine expression API ----------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "mlir/IR/AffineExpr.h"
+#include "mlir/IR/Builders.h"
+#include "gtest/gtest.h"
+
+using namespace mlir;
+
+// Test creating AffineExprs using the overloaded binary operators.
+TEST(AffineExprTest, constructFromBinaryOperators) {
+  MLIRContext ctx;
+  OpBuilder b(&ctx);
+
+  auto d0 = b.getAffineDimExpr(0);
+  auto d1 = b.getAffineDimExpr(1);
+
+  auto sum = d0 + d1;
+  auto difference = d0 - d1;
+  auto product = d0 * d1;
+  auto remainder = d0 % d1;
+
+  ASSERT_EQ(sum.getKind(), AffineExprKind::Add);
+  ASSERT_EQ(difference.getKind(), AffineExprKind::Add);
+  ASSERT_EQ(product.getKind(), AffineExprKind::Mul);
+  ASSERT_EQ(remainder.getKind(), AffineExprKind::Mod);
+}

mlir/unittests/IR/CMakeLists.txt

@@ -1,5 +1,6 @@
 add_mlir_unittest(MLIRIRTests
   AdaptorTest.cpp
+  AffineExprTest.cpp
   AffineMapTest.cpp
   AttributeTest.cpp
   DialectTest.cpp