Fix GCC 12.1.1 LTO -Walloc-size-larger-than= warnings

With -flto=auto, GCC emits multiple warnings in release builds such as

In function ‘make_unique’,
    inlined from ‘Create’ at ceres-solver/internal/ceres/scratch_evaluate_preparer.cc:43:75,
    inlined from ‘CreateEvaluatePreparers’ at ceres-solver/internal/ceres/compressed_row_jacobian_writer.h:95:66,
    inlined from ‘__ct ’ at ceres-solver/internal/ceres/program_evaluator.h:120:9,
    inlined from ‘Evaluate.constprop.isra’ at ceres-solver/internal/ceres/problem_impl.cc:695:65:
/usr/include/c++/12.1.1/bits/unique_ptr.h:1080:30: warning: argument 1 value ‘18446744073709551615’ exceeds maximum object size 9223372036854775807 [-Walloc-size-larger-than=]
 1080 |     { return unique_ptr<_Tp>(new remove_extent_t<_Tp>[__num]()); }
      |                              ^

because a signed integer is used to specify the size of allocated arrays
instead of the expected unsigned (specifically, std::size_t) without
checking for negative values at the call site.

Change-Id: I923b1d074241535426bfea041568ef1dc7f3ec86

internal/ceres/block_jacobian_writer.cc

@@ -138,12 +138,12 @@ BlockJacobianWriter::BlockJacobianWriter(const Evaluator::Options& options,
 // Create evaluate prepareres that point directly into the final jacobian. This
 // makes the final Write() a nop.
 std::unique_ptr<BlockEvaluatePreparer[]>
-BlockJacobianWriter::CreateEvaluatePreparers(int num_threads) {
+BlockJacobianWriter::CreateEvaluatePreparers(unsigned num_threads) {
   int max_derivatives_per_residual_block =
       program_->MaxDerivativesPerResidualBlock();
 
   auto preparers = std::make_unique<BlockEvaluatePreparer[]>(num_threads);
-  for (int i = 0; i < num_threads; i++) {
+  for (unsigned i = 0; i < num_threads; i++) {
     preparers[i].Init(&jacobian_layout_[0], max_derivatives_per_residual_block);
   }
   return preparers;

internal/ceres/block_jacobian_writer.h

@@ -60,7 +60,7 @@ class CERES_NO_EXPORT BlockJacobianWriter {
   // Create evaluate prepareres that point directly into the final jacobian.
   // This makes the final Write() a nop.
   std::unique_ptr<BlockEvaluatePreparer[]> CreateEvaluatePreparers(
-      int num_threads);
+      unsigned num_threads);
 
   std::unique_ptr<SparseMatrix> CreateJacobian() const;
 

internal/ceres/program_evaluator.h

@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2015 Google Inc. All rights reserved.
+// Copyright 2022 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without
@@ -129,8 +129,8 @@ class ProgramEvaluator final : public Evaluator {
 #endif  // CERES_NO_THREADS
 
     BuildResidualLayout(*program, &residual_layout_);
-    evaluate_scratch_ =
-        std::move(CreateEvaluatorScratch(*program, options.num_threads));
+    evaluate_scratch_ = std::move(CreateEvaluatorScratch(
+        *program, static_cast<unsigned>(options.num_threads)));
   }
 
   // Implementation of Evaluator interface.
@@ -345,7 +345,7 @@ class ProgramEvaluator final : public Evaluator {
 
   // Create scratch space for each thread evaluating the program.
   static std::unique_ptr<EvaluateScratch[]> CreateEvaluatorScratch(
-      const Program& program, int num_threads) {
+      const Program& program, unsigned num_threads) {
     int max_parameters_per_residual_block =
         program.MaxParametersPerResidualBlock();
     int max_scratch_doubles_needed_for_evaluate =

internal/ceres/scratch_evaluate_preparer.cc

@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2015 Google Inc. All rights reserved.
+// Copyright 2022 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without
@@ -39,19 +39,19 @@
 namespace ceres::internal {
 
 std::unique_ptr<ScratchEvaluatePreparer[]> ScratchEvaluatePreparer::Create(
-    const Program& program, int num_threads) {
+    const Program& program, unsigned num_threads) {
   auto preparers = std::make_unique<ScratchEvaluatePreparer[]>(num_threads);
   int max_derivatives_per_residual_block =
       program.MaxDerivativesPerResidualBlock();
-  for (int i = 0; i < num_threads; i++) {
+  for (unsigned i = 0; i < num_threads; i++) {
     preparers[i].Init(max_derivatives_per_residual_block);
   }
   return preparers;
 }
 
 void ScratchEvaluatePreparer::Init(int max_derivatives_per_residual_block) {
-  jacobian_scratch_ =
-      std::make_unique<double[]>(max_derivatives_per_residual_block);
+  jacobian_scratch_ = std::make_unique<double[]>(
+      static_cast<std::size_t>(max_derivatives_per_residual_block));
 }
 
 // Point the jacobian blocks into the scratch area of this evaluate preparer.

internal/ceres/scratch_evaluate_preparer.h

@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2015 Google Inc. All rights reserved.
+// Copyright 2022 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without
@@ -50,7 +50,7 @@ class CERES_NO_EXPORT ScratchEvaluatePreparer {
  public:
   // Create num_threads ScratchEvaluatePreparers.
   static std::unique_ptr<ScratchEvaluatePreparer[]> Create(
-      const Program& program, int num_threads);
+      const Program& program, unsigned num_threads);
 
   // EvaluatePreparer interface
   void Init(int max_derivatives_per_residual_block);