[mlir][ValueBounds] memref.dim and tensor.dim are always positive (#122804)

Add the constraint that the length of a memref or tensor dimension is
always non-negative (at least 0) even if we don't know which dimension
we're querying the length of.

Author: krzysz00

mlir/lib/Dialect/MemRef/IR/ValueBoundsOpInterfaceImpl.cpp

@@ -51,6 +51,7 @@ struct DimOpInterface
     auto dimOp = cast<DimOp>(op);
     assert(value == dimOp.getResult() && "invalid value");
 
+    cstr.bound(value) >= 0;
     auto constIndex = dimOp.getConstantIndex();
     if (!constIndex.has_value())
       return;

mlir/lib/Dialect/Tensor/IR/ValueBoundsOpInterfaceImpl.cpp

@@ -38,6 +38,7 @@ struct DimOpInterface
     auto dimOp = cast<DimOp>(op);
     assert(value == dimOp.getResult() && "invalid value");
 
+    cstr.bound(value) >= 0;
     auto constIndex = dimOp.getConstantIndex();
     if (!constIndex.has_value())
       return;

mlir/test/Dialect/MemRef/value-bounds-op-interface-impl.mlir

@@ -52,6 +52,17 @@ func.func @memref_dim(%m: memref<?xf32>) -> index {
 
 // -----
 
+// CHECK-LABEL: func @memref_dim_all_positive(
+func.func @memref_dim_all_positive(%m: memref<?xf32>, %x: index) {
+  %c0 = arith.constant 0 : index
+  %0 = memref.dim %m, %x : memref<?xf32>
+  // expected-remark @below{{true}}
+  "test.compare"(%0, %c0) {cmp = "GE"} : (index, index) -> ()
+  return
+}
+
+// -----
+
 // CHECK-LABEL: func @memref_get_global(
 //       CHECK:   %[[c4:.*]] = arith.constant 4 : index
 //       CHECK:   return %[[c4]]

mlir/test/Dialect/Tensor/value-bounds-op-interface-impl.mlir

@@ -44,6 +44,17 @@ func.func @dim(%t: tensor<?xf32>) -> index {
 
 // -----
 
+// CHECK-LABEL: func @dim_all_positive(
+func.func @dim_all_positive(%t: tensor<?xf32>, %x: index) {
+  %c0 = arith.constant 0 : index
+  %0 = tensor.dim %t, %x : tensor<?xf32>
+  // expected-remark @below{{true}}
+  "test.compare"(%0, %c0) {cmp = "GE" } : (index, index) -> ()
+  return
+}
+
+// -----
+
 // CHECK-LABEL: func @empty(
 //  CHECK-SAME:     %[[sz:.*]]: index
 //       CHECK:   %[[c6:.*]] = arith.constant 6 : index