[mlir][tosa] Fix check for isolated regions in tosa.cond_if (#143772)

This commit fixes a check in the validation pass which intended to
validate whether a `tosa.cond_if` operation was conformant to the
specification. The specification requires all values used in the
then/else regions are explicitly declared within the regions. This
change checks that these regions are 'isolated from above', to ensure
this requirement is true.

Author: lhutton1

mlir/lib/Dialect/Tosa/Transforms/TosaValidation.cpp

@@ -1193,32 +1193,55 @@ bool checkErrorIfPad(Operation *op) {
   return true;
 }
 
-// Returns true if the operation takes no input operands, excluding attributes.
-static bool isNullaryOperation(Operation *op) {
-  if (isa<tosa::ConstOp>(op) || isa<tosa::ConstShapeOp>(op) ||
-      isa<tosa::YieldOp>(op) || isa<tosa::VariableOp>(op))
-    return true;
-  return false;
+static bool isOpIsolatedWithinRegion(Operation *op, Region *region) {
+  return llvm::all_of(op->getOperands(), [&](auto operand) {
+    Region *operandRegion = operand.getParentRegion();
+    return operandRegion && region->isAncestor(operandRegion);
+  });
 }
 
 bool checkErrorIfCondIf(Operation *op) {
   auto ifOp = dyn_cast<tosa::IfOp>(op);
   if (!ifOp)
     return true;
 
-  // Whether the types and shapes of operands between the input/output list and
-  // internal regions are validated by the operation verifier. However, with
-  // support for the simplified form - where redundant operand notations are
-  // omitted - is not conformant to the specification. According to the
-  // specification, all operands passed into an operation must be explicitly
-  // declared at each operation's structure. This code section verify that the
-  // operation's form complies with this requirement.
+  // Currently the dialect supports declaring cond_if operations that
+  // have then/else regions that reference values from outside these
+  // regions. According to the specification, all values used by the
+  // then/else regions must be explicitly declared within the regions.
+  // Therefore we must check that the then/else regions are
+  // "isolated from above", in order to be conformant to the
+  // specification.
+  //
+  // Note: the dialect currently supports two styles of syntax for
+  // declaring "cond_if" operations. We'll refer to these as follows:
+  //
+  // Generic:
+  // %0 = "tosa.cond_if"(%arg0, %arg1, %arg2) ({
+  //   ^bb0(%arg3, %arg4):
+  //     tosa.yield %arg3
+  // },  {
+  //   ^bb0(%arg3, %arg4):
+  //     tosa.yield %arg4
+  // })
+  //
+  // Simplified:
+  // %0 = tosa.cond_if %arg2 {
+  //   tosa.yield %arg0
+  // } else {
+  //   tosa.yield %arg1
+  // }
+  //
+  // Unfortunately, the simplified syntax does not encapsulate values
+  // used in then/else regions (see 'simplified' example above), so it
+  // must be rewritten to use the generic syntax in order to be conformant
+  // to the specification.
 
   // Returns true if the region uses no external input operands.
-  auto isNullaryRegion = [](Region &region) -> bool {
+  auto isIsolatedRegion = [](Region &regionToCheck) -> bool {
     bool noLiveInValue = true;
-    region.walk([&noLiveInValue](Operation *op) {
-      if (!isNullaryOperation(op)) {
+    regionToCheck.walk([&noLiveInValue, &regionToCheck](Operation *opInRegion) {
+      if (!isOpIsolatedWithinRegion(opInRegion, &regionToCheck)) {
         noLiveInValue = false;
         return WalkResult::interrupt();
       }
@@ -1227,21 +1250,18 @@ bool checkErrorIfCondIf(Operation *op) {
     return noLiveInValue;
   };
 
-  mlir::Region &thenGraph = ifOp.getThenGraph();
-  mlir::Region &elseGraph = ifOp.getElseGraph();
-  bool isThenGraphNullaryRegion = isNullaryRegion(thenGraph);
-  bool isElseGraphNullaryRegion = isNullaryRegion(elseGraph);
-  bool isInputListEmpty = ifOp.getInputList().size() == 0;
-
-  if ((isInputListEmpty != isThenGraphNullaryRegion) ||
-      (isInputListEmpty != isElseGraphNullaryRegion)) {
+  auto checkIsolatedRegion = [&](Region &regionToCheck,
+                                 StringRef regionName) -> LogicalResult {
+    if (isIsolatedRegion(regionToCheck))
+      return success();
     op->emitOpError()
-        << "the current simplified form is not strictly conformant to the "
-           "spec, please use the generic format\n";
-    return false;
-  }
+        << "is not conformant to the TOSA specification. It requires the '"
+        << regionName << "' region is isolated from above.\n";
+    return failure();
+  };
 
-  return true;
+  return failed(checkIsolatedRegion(ifOp.getThenGraph(), "then")) ||
+         failed(checkIsolatedRegion(ifOp.getElseGraph(), "else"));
 }
 
 bool checkErrorIfScatter(Operation *op) {

mlir/test/Dialect/Tosa/error_if_check.mlir

@@ -227,15 +227,56 @@ func.func @test_error_i32_unsigned_output(%arg0: tensor<1xi8>) -> tensor<1xi32>
 }
 
 // -----
-// CHECK-LABEL: cond_if_simplified_form
-func.func @test_cond_if_simplified_form(%arg0: tensor<f32>, %arg1: tensor<f32>, %arg2: tensor<i1>) -> tensor<f32> {
-  // expected-error@+1 {{'tosa.cond_if' op the current simplified form is not strictly conformant to the spec, please use the generic format}}
+
+func.func @test_cond_if_then_not_isolated_from_above(%arg0: tensor<f32>, %arg1: tensor<f32>, %arg2: tensor<i1>) -> tensor<f32> {
+    // expected-error@+1 {{'tosa.cond_if' op is not conformant to the TOSA specification. It requires the 'then' region is isolated from above.}}
+    %0 = "tosa.cond_if"(%arg2, %arg1) ({
+      ^bb0(%arg3: tensor<f32>):
+        tosa.yield %arg1 : tensor<f32>
+      },  {
+      ^bb0(%arg3: tensor<f32>):
+        tosa.yield %arg3 : tensor<f32>
+      }) : (tensor<i1>, tensor<f32>) -> tensor<f32>
+    return %0 : tensor<f32>
+}
+
+// -----
+
+func.func @test_cond_if_else_not_isolated_from_above(%arg0: tensor<f32>, %arg1: tensor<f32>, %arg2: tensor<i1>) -> tensor<f32> {
+  // expected-error@+1 {{'tosa.cond_if' op is not conformant to the TOSA specification. It requires the 'else' region is isolated from above.}}
+  %0 = "tosa.cond_if"(%arg2, %arg0, %arg1) ({
+    ^bb0(%arg3: tensor<f32>, %arg4: tensor<f32>):
+      tosa.yield %arg3 : tensor<f32>
+    },  {
+    ^bb0(%arg3: tensor<f32>, %arg4: tensor<f32>):
+      %add = tosa.add %arg0, %arg4 : (tensor<f32>, tensor<f32>) -> tensor<f32>
+      tosa.yield %add : tensor<f32>
+    }) : (tensor<i1>, tensor<f32>, tensor<f32>) -> tensor<f32>
+  return %0 : tensor<f32>
+}
+
+// -----
+
+func.func @test_cond_if_simplified_form_not_isolated_from_above(%arg0: tensor<f32>, %arg1: tensor<f32>, %arg2: tensor<i1>) -> tensor<f32> {
+  // expected-error@+1 {{'tosa.cond_if' op is not conformant to the TOSA specification. It requires the 'then' region is isolated from above.}}
   %0 = tosa.cond_if %arg2 -> (tensor<f32>) {
-    %1 = tosa.add %arg0, %arg1 : (tensor<f32>, tensor<f32>) -> tensor<f32>
-    tosa.yield %1 : tensor<f32>
+    tosa.yield %arg0 : tensor<f32>
   } else {
-    %1 = tosa.sub %arg0, %arg1 : (tensor<f32>, tensor<f32>) -> tensor<f32>
-    tosa.yield %1 : tensor<f32>
+    tosa.yield %arg1 : tensor<f32>
   }
   return %0 : tensor<f32>
 }
+
+// -----
+
+// Check isolated cond_if's are valid
+func.func @test_cond_if_isolated_from_above(%arg0: tensor<f32>, %arg1: tensor<f32>, %arg2: tensor<i1>) -> tensor<f32> {
+  %0 = "tosa.cond_if"(%arg2, %arg0, %arg1) ({
+    ^bb0(%arg3: tensor<f32>, %arg4: tensor<f32>):
+      tosa.yield %arg3 : tensor<f32>
+    },  {
+    ^bb0(%arg3: tensor<f32>, %arg4: tensor<f32>):
+      tosa.yield %arg4 : tensor<f32>
+    }) : (tensor<i1>, tensor<f32>, tensor<f32>) -> tensor<f32>
+  return %0 : tensor<f32>
+}