Add diagnostics for read accessors

Author: asavonic

include/swift/AST/DiagnosticsSIL.def

@@ -592,6 +592,8 @@ NOTE(autodiff_cannot_differentiate_through_multiple_results,none,
      "cannot differentiate through multiple results", ())
 NOTE(autodiff_cannot_differentiate_through_inout_arguments,none,
      "cannot differentiate through 'inout' arguments", ())
+NOTE(autodiff_cannot_differentiate_through_direct_yield,none,
+     "cannot differentiate through a direct yield result", ())
 NOTE(autodiff_enums_unsupported,none,
      "differentiating enum values is not yet supported", ())
 NOTE(autodiff_stored_property_parent_not_differentiable,none,

lib/SILOptimizer/Differentiation/VJPCloner.cpp

@@ -564,6 +564,12 @@ class VJPCloner::Implementation final
         // We do not have a good way to differentiate direct yields
         if (yield.isAutoDiffSemanticResult())
           remappedResultType = yield.getSILStorageInterfaceType();
+        else {
+          context.emitNondifferentiabilityError(
+              origCallee, invoker,
+              diag::autodiff_cannot_differentiate_through_direct_yield);
+          return true;
+        }
       } else if (resultIndex >= firstSemanticParamResultIdx) {
         auto semanticResultArgIdx = resultIndex - firstSemanticParamResultIdx;
         auto semanticResultArg =

lib/SILOptimizer/Mandatory/Differentiation.cpp

@@ -157,18 +157,18 @@ static bool diagnoseUnsupportedControlFlow(ADContext &context,
         isa<CheckedCastAddrBranchInst>(term) || isa<TryApplyInst>(term))
       continue;
 
-    // We can differentiate only indirect yields
+    // We can differentiate only indirect yields.
     if (auto *yi = dyn_cast<YieldInst>(term)) {
-      for (const auto &val : yi->getAllOperands())
-        if (!yi->getYieldInfoForOperand(val).isAutoDiffSemanticResult()) {
-          context.emitNondifferentiabilityError(
-            term, invoker, diag::autodiff_control_flow_not_supported);
-          return true;
-        }
-
+#ifndef NDEBUG
+      for (const auto &val : yi->getAllOperands()) {
+        // This should be diagnosed earlier in VJPCloner.
+        assert(yi->getYieldInfoForOperand(val).isAutoDiffSemanticResult() &&
+               "unsupported result");
+      }
+#endif
       continue;
     }
-    
+
     // If terminator is an unsupported branching terminator, emit an error.
     if (term->isBranch()) {
       context.emitNondifferentiabilityError(
@@ -562,9 +562,10 @@ emitDerivativeFunctionReference(
         if (resultIndex >= firstYieldResultIndex) {
           auto yieldResultIndex = resultIndex - firstYieldResultIndex;
           auto yield = originalFnTy->getYields()[yieldResultIndex];
-          // We can only differentiate indirect yields
-          if (yield.isAutoDiffSemanticResult())
-            resultType = yield.getSILStorageInterfaceType();
+          // We can only differentiate indirect yields. This should be diagnosed
+          // earlier in VJPCloner.
+          assert(yield.isAutoDiffSemanticResult() && "unsupported result");
+          resultType = yield.getSILStorageInterfaceType();
         } else if (resultIndex >= firstSemanticParamResultIdx) {
           auto semanticResultParamIdx = resultIndex - firstSemanticParamResultIdx;
           auto semanticResultParam =

test/AutoDiff/SILOptimizer/activity_analysis.swift

@@ -594,7 +594,7 @@ struct HasCoroutineModifyAccessors: Differentiable {
 // expected-note @+1 {{when differentiating this function definition}}
 func testAccessorCoroutinesRead(_ x: HasCoroutineReadAccessors) -> Float {
   // We do not support differentiation of _read accessors
-  // expected-note @+1 {{cannot differentiate through a non-differentiable result; do you want to use 'withoutDerivative(at:)}}
+  // expected-note @+1 {{cannot differentiate through a direct yield result}}
   return x.computed
 }
 

test/AutoDiff/SILOptimizer/differentiation_diagnostics.swift

@@ -826,7 +826,7 @@ struct HasModifyAccessors: Differentiable {
 // expected-note @+2 {{when differentiating this function definition}}
 @differentiable(reverse)
 func testReadAccessorCoroutines(_ x: HasReadAccessors) -> Float {
-  // expected-note @+1 {{cannot differentiate through a non-differentiable result; do you want to use 'withoutDerivative(at:)'?}}
+  // expected-note @+1 {{cannot differentiate through a direct yield result}}
   return x.computed
 }