[Phi] Fix infermeta bug for vector input and output (#45810)

* fix infermeta bug for vector input and output

* add unittest

paddle/fluid/framework/infershape_utils.cc

@@ -459,6 +459,9 @@ CompatInferMetaContext BuildInferMetaContext(InferShapeContext* ctx,
         infer_meta_context.EmplaceBackInputs(std::move(inputs));
       }
     } else {
+      // Note: Because the input of InferMetaFn is const MetaTensor&,
+      // so when we prepare input MetaTensor by InferMetaContext->InputAt(),
+      // we need to return a const reference of empty MetaTensor
       infer_meta_context.EmplaceBackInput(
           std::move(CompatMetaTensor(ctx->IsRuntime())));
     }

paddle/phi/core/infermeta_utils.cc

@@ -68,8 +68,13 @@ const MetaTensor& InferMetaContext::InputAt(size_t idx) const {
 std::vector<const MetaTensor*> InferMetaContext::InputsBetween(
     size_t start, size_t end) const {
   std::vector<const MetaTensor*> result;
-  result.reserve(end - start);
+  // If vector only contains one input that is not initialized,
+  // we should return a empty vector
+  if (end - start == 1 && !inputs_.at(start).initialized()) {
+    return result;
+  }
 
+  result.reserve(end - start);
   for (size_t i = start; i < end; ++i) {
     auto& in = inputs_.at(i);
     result.emplace_back(in.initialized() ? &in : nullptr);
@@ -104,6 +109,12 @@ MetaTensor* InferMetaContext::MutableOutputAt(size_t idx) {
 std::vector<MetaTensor*> InferMetaContext::MutableOutputBetween(size_t start,
                                                                 size_t end) {
   std::vector<MetaTensor*> result;
+  // If vector only contains one output that is not initialized,
+  // we should return a empty vector
+  if (end - start == 1 && !outputs_.at(start).initialized()) {
+    return result;
+  }
+
   result.reserve(end - start);
   for (size_t i = start; i < end; ++i) {
     auto& out = outputs_.at(i);

paddle/phi/tests/core/test_meta_fn_utils.cc

@@ -91,5 +91,19 @@ TEST(MetaFnFactory, SplitInferMetaFn) {
   ASSERT_EQ(dense_out2.dims()[1], 10);
 }
 
+void TestEmptyVectorInputInferMeta(const std::vector<const MetaTensor*>& inputs,
+                                   std::vector<MetaTensor*> outputs) {
+  ASSERT_EQ(inputs.size(), 0UL);
+  ASSERT_EQ(outputs.size(), 0UL);
+}
+
+TEST(MetaFnFactory, EmptyVectorInputInferMetaFn) {
+  phi::InferMetaContext ctx;
+  ctx.EmplaceBackInput(MetaTensor());
+  ctx.EmplaceBackOutput(MetaTensor());
+
+  PD_INFER_META(TestEmptyVectorInputInferMeta)(&ctx);
+}
+
 }  // namespace tests
 }  // namespace phi