From ff402cc563c2bd84568bb26ab888bb523489aabe Mon Sep 17 00:00:00 2001
From: Samuel Benzaquen <sbenza@google.com>
Date: Mon, 20 Apr 2026 10:32:51 -0700
Subject: [PATCH] Add PROTOBUF_ASSUME annotations to specify that size() is
 non-negative.

This allows the compiler to optimize bound checking code.

PiperOrigin-RevId: 902708802
---
 src/google/protobuf/repeated_field.h          | 10 ++++++--
 .../protobuf/repeated_field_unittest.cc       |  8 +++++++
 src/google/protobuf/repeated_ptr_field.h      | 24 ++++++++++++-------
 .../protobuf/repeated_ptr_field_unittest.cc   |  8 +++++++
 4 files changed, 40 insertions(+), 10 deletions(-)

diff --git a/src/google/protobuf/repeated_field.h b/src/google/protobuf/repeated_field.h
index fc3a06f455452..db4a296b09e7a 100644
--- a/src/google/protobuf/repeated_field.h
+++ b/src/google/protobuf/repeated_field.h
@@ -191,7 +191,11 @@ class SooRep {
   Arena* arena() const {
     return ResolveTaggedArena<&SooRep::resolver_, kResolverTaggedBits>(this);
   }
-  int size() const { return size_; }
+  int size() const {
+    int res = size_;
+    PROTOBUF_ASSUME(res >= 0);
+    return res;
+  }
   void set_size(int size) {
     ABSL_DCHECK(!is_soo() || size <= kSooCapacityBytes);
     size_ = size;
@@ -559,7 +563,9 @@ class ABSL_ATTRIBUTE_WARN_UNUSED PROTOBUF_DECLSPEC_EMPTY_BASES
     soo_rep_.set_size(size);
   }
   int Capacity(bool is_soo) const {
-    return is_soo ? kSooCapacityElements : soo_rep_.capacity();
+    int res = is_soo ? kSooCapacityElements : soo_rep_.capacity();
+    PROTOBUF_ASSUME(res >= 0);
+    return res;
   }
 
   template <typename ArenaProvider>
diff --git a/src/google/protobuf/repeated_field_unittest.cc b/src/google/protobuf/repeated_field_unittest.cc
index 35affbfca01d3..4edf0f9b9e884 100644
--- a/src/google/protobuf/repeated_field_unittest.cc
+++ b/src/google/protobuf/repeated_field_unittest.cc
@@ -1620,4 +1620,12 @@ TEST(RepeatedFieldIsFullTest, DISABLED_MergeFromPacked) {
 }  // namespace protobuf
 }  // namespace google
 
+// Code thunks to be dumped by the debugger to inspect the generated assemtbly.
+static const int& CodegenRepeatedFieldGet(const google::protobuf::RepeatedField<int>& a,
+                                          int idx) {
+  return a[idx];
+}
+
+static volatile int odr_use = absl::HashOf(&CodegenRepeatedFieldGet);
+
 #include "google/protobuf/port_undef.inc"
diff --git a/src/google/protobuf/repeated_ptr_field.h b/src/google/protobuf/repeated_ptr_field.h
index 048713f7ae931..efd7926bdeea0 100644
--- a/src/google/protobuf/repeated_ptr_field.h
+++ b/src/google/protobuf/repeated_ptr_field.h
@@ -224,14 +224,22 @@ class PROTOBUF_EXPORT RepeatedPtrFieldBase {
   }
 
   bool empty() const { return current_size_ == 0; }
-  int size() const { return current_size_; }
+  int size() const {
+    int res = current_size_;
+    PROTOBUF_ASSUME(res >= 0);
+    return res;
+  }
   // Returns the size of the buffer with pointers to elements.
   //
   // Note:
   //
   //   * prefer `SizeAtCapacity()` to `size() == Capacity()`;
   //   * prefer `AllocatedSizeAtCapacity()` to `allocated_size() == Capacity()`.
-  int Capacity() const { return using_sso() ? kSSOCapacity : rep()->capacity; }
+  int Capacity() const {
+    int res = using_sso() ? kSSOCapacity : rep()->capacity;
+    PROTOBUF_ASSUME(res >= 0);
+    return res;
+  }
 
   template <typename TypeHandler>
   const Value<TypeHandler>& at(int index) const {
@@ -249,7 +257,7 @@ class PROTOBUF_EXPORT RepeatedPtrFieldBase {
 
   template <typename TypeHandler>
   Value<TypeHandler>* Mutable(int index) {
-    RuntimeAssertInBounds(index, current_size_);
+    RuntimeAssertInBounds(index, size());
     return cast<TypeHandler>(element_at(index));
   }
 
@@ -340,7 +348,7 @@ class PROTOBUF_EXPORT RepeatedPtrFieldBase {
   template <typename TypeHandler>
   PROTOBUF_FUTURE_ADD_NODISCARD const Value<TypeHandler>& Get(int index) const {
     if constexpr (GetBoundsCheckMode() == BoundsCheckMode::kReturnDefault) {
-      if (ABSL_PREDICT_FALSE(index < 0 || index >= current_size_)) {
+      if (ABSL_PREDICT_FALSE(index < 0 || index >= size())) {
         // `default_instance()` is not supported for MessageLite and Message.
         if constexpr (TypeHandler::has_default_instance()) {
           LogIndexOutOfBounds(index, current_size_);
@@ -350,7 +358,7 @@ class PROTOBUF_EXPORT RepeatedPtrFieldBase {
     }
     // We refactor this to a separate function instead of inlining it so we
     // can measure the performance impact more easily.
-    RuntimeAssertInBounds(index, current_size_);
+    RuntimeAssertInBounds(index, size());
     return *cast<TypeHandler>(element_at(index));
   }
 
@@ -518,8 +526,8 @@ class PROTOBUF_EXPORT RepeatedPtrFieldBase {
   }
 
   void SwapElements(int index1, int index2) {
-    internal::RuntimeAssertInBounds(index1, current_size_);
-    internal::RuntimeAssertInBounds(index2, current_size_);
+    internal::RuntimeAssertInBounds(index1, size());
+    internal::RuntimeAssertInBounds(index2, size());
     using std::swap;  // enable ADL with fallback
     swap(element_at(index1), element_at(index2));
   }
@@ -625,7 +633,7 @@ class PROTOBUF_EXPORT RepeatedPtrFieldBase {
   // arena.
   template <typename TypeHandler>
   Value<TypeHandler>* UnsafeArenaReleaseLast() {
-    internal::RuntimeAssertInBounds(0, current_size_);
+    internal::RuntimeAssertInBounds(0, size());
     ExchangeCurrentSize(current_size_ - 1);
     auto* result = cast<TypeHandler>(element_at(current_size_));
     if (using_sso()) {
diff --git a/src/google/protobuf/repeated_ptr_field_unittest.cc b/src/google/protobuf/repeated_ptr_field_unittest.cc
index f3d9ac28d56ad..52284e14b48ff 100644
--- a/src/google/protobuf/repeated_ptr_field_unittest.cc
+++ b/src/google/protobuf/repeated_ptr_field_unittest.cc
@@ -2029,4 +2029,12 @@ TEST_F(RepeatedPtrFieldInsertionIteratorsTest, MoveProtos) {
 }  // namespace protobuf
 }  // namespace google
 
+// Code thunks to be dumped by the debugger to inspect the generated assemtbly.
+static auto& CodegenRepeatedPtrFieldGet(
+    const google::protobuf::RepeatedPtrField<std::string>& a, int idx) {
+  return a[idx];
+}
+
+static volatile int odr_use = absl::HashOf(&CodegenRepeatedPtrFieldGet);
+
 #include "google/protobuf/port_undef.inc"