Avoid forwarding a bounds-checked subscript operation, closes #799

Author: hsutter

include/cpp2util.h

@@ -457,22 +457,22 @@ auto assert_not_null(auto&& p CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> declty
 
 //  Subscript bounds checking
 //
-auto assert_in_bounds(auto&& x, auto&& arg CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> decltype(auto)
+auto assert_in_bounds_impl(auto&& x, auto&& arg CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> void
     requires (std::is_integral_v<CPP2_TYPEOF(arg)> &&
              requires { std::size(x); std::ssize(x); x[arg]; std::begin(x) + 2; })
 {
     Bounds.expects(0 <= arg && arg < [&]() -> auto {
         if constexpr (std::is_signed_v<CPP2_TYPEOF(arg)>) { return std::ssize(x); }
         else { return std::size(x); }
     }(), "out of bounds access attempt detected" CPP2_SOURCE_LOCATION_ARG);
-    return CPP2_FORWARD(x) [ CPP2_FORWARD(arg) ];
 }
 
-auto assert_in_bounds(auto&& x, auto&& arg CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> decltype(auto)
+auto assert_in_bounds_impl(auto&&, auto&& CPP2_SOURCE_LOCATION_PARAM_WITH_DEFAULT) -> void
 {
-    return CPP2_FORWARD(x) [ CPP2_FORWARD(arg) ];
 }
 
+#define CPP2_ASSERT_IN_BOUNDS(x, arg) (cpp2::assert_in_bounds_impl((x),(arg)), (x)[(arg)])
+
 
 //-----------------------------------------------------------------------
 //

regression-tests/test-results/mixed-bounds-check.cpp

@@ -27,6 +27,6 @@
 
     std::vector v {1, 2, 3, 4, 5, -999}; 
     CPP2_UFCS_0(pop_back, v);
-    std::cout << cpp2::assert_in_bounds(std::move(v), 5) << "\n";
+    std::cout << CPP2_ASSERT_IN_BOUNDS(std::move(v), 5) << "\n";
 }
 

regression-tests/test-results/mixed-test-parens.cpp

@@ -28,7 +28,7 @@ constexpr int a = 1;
 #line 8 "mixed-test-parens.cpp2"
 [[nodiscard]] auto main() -> int{
     std::vector<int> v {1, 2, 3}; 
-    std::cout << (1 + 2) * (3 + cpp2::assert_in_bounds(std::move(v), 0));
+    std::cout << (1 + 2) * (3 + CPP2_ASSERT_IN_BOUNDS(std::move(v), 0));
     f<(cpp2::cmp_greater(1,2))>(3, 4);
     f<a + a>(5, 6);
 }

regression-tests/test-results/pure2-bounds-safety-span.cpp

@@ -36,7 +36,7 @@ auto print_and_decorate(auto const& thing) -> void;
 
     auto i {0}; 
     for( ; cpp2::cmp_less(i,CPP2_UFCS_0(ssize, s)); ++i ) {
-        print_and_decorate(cpp2::assert_in_bounds(s, i));
+        print_and_decorate(CPP2_ASSERT_IN_BOUNDS(s, i));
     }
 }
 

regression-tests/test-results/pure2-bugfix-for-non-local-initialization.cpp

@@ -28,7 +28,7 @@ auto main() -> int;
 
 #line 5 "pure2-bugfix-for-non-local-initialization.cpp2"
 auto main() -> int{
-  cpp2::Testing.expects(cpp2::assert_in_bounds(t::value, 0) == 17, "");
-  cpp2::Testing.expects(cpp2::assert_in_bounds(t::value, 1) == 29, "");
+  cpp2::Testing.expects(CPP2_ASSERT_IN_BOUNDS(t::value, 0) == 17, "");
+  cpp2::Testing.expects(CPP2_ASSERT_IN_BOUNDS(t::value, 1) == 29, "");
 }
 

regression-tests/test-results/pure2-intro-example-three-loops.cpp

@@ -45,7 +45,7 @@ auto decorate_and_print(auto& thing) -> void{
 
     auto i {cpp2_new<int>(0)}; 
     for( ; cpp2::cmp_less(*cpp2::assert_not_null(i),CPP2_UFCS_0(ssize, view)); ++*cpp2::assert_not_null(i) ) {
-        print(cpp2::assert_in_bounds(view, *cpp2::assert_not_null(i)));
+        print(CPP2_ASSERT_IN_BOUNDS(view, *cpp2::assert_not_null(i)));
     }
 
     do {

regression-tests/test-results/pure2-main-args.cpp

@@ -22,5 +22,5 @@ auto main(int const argc_, char** argv_) -> int {
 #line 2 "pure2-main-args.cpp2"
     std::cout 
         << "args.argc            is " + cpp2::to_string(args.argc) + "\n" 
-        << "args.argv[0]         is " + cpp2::to_string(cpp2::assert_in_bounds(args.argv, 0)) + "\n"; }
+        << "args.argv[0]         is " + cpp2::to_string(CPP2_ASSERT_IN_BOUNDS(args.argv, 0)) + "\n"; }
 

regression-tests/test-results/pure2-print.cpp

@@ -102,7 +102,7 @@ requires (true) inline CPP2_CONSTEXPR T outer::object_alias = 42;
             ret += strlen(s) - 10 + CPP2_UFCS_0(strlen, std::move(s)) * (16 / (3 & 2)) % 3;
 
             map<int const,string> m {}; 
-            cpp2::assert_in_bounds(m, 0) = cpp2::as_<string>("har");
+            CPP2_ASSERT_IN_BOUNDS(m, 0) = cpp2::as_<string>("har");
             ret -= CPP2_UFCS_0(length, h("x", m));
             static_cast<void>(std::move(m));
 
@@ -133,7 +133,7 @@ requires (true) inline CPP2_CONSTEXPR T outer::object_alias = 42;
 
             cpp2::Default.expects(true, "");
 
-            return [_0 = (s + cpp2::assert_in_bounds(m, 0))]() -> std::string { return _0;  }(); 
+            return [_0 = (s + CPP2_ASSERT_IN_BOUNDS(m, 0))]() -> std::string { return _0;  }(); 
         }
 
         template<typename T> [[nodiscard]] auto outer::mytype::values([[maybe_unused]] T const& unnamed_param_2) const& -> values_ret{

regression-tests/test-results/pure2-raw-string-literal-and-interpolation.cpp

@@ -21,8 +21,8 @@
 #line 2 "pure2-raw-string-literal-and-interpolation.cpp2"
     auto i {42}; 
     std::map<std::string,int> m {}; 
-    cpp2::assert_in_bounds(m, "one") = 1;
-    cpp2::assert_in_bounds(m, "two") = 2;
+    CPP2_ASSERT_IN_BOUNDS(m, "one") = 1;
+    CPP2_ASSERT_IN_BOUNDS(m, "two") = 2;
 
     std::string str {"this is a string"}; 
 
@@ -38,7 +38,7 @@ lines)test"};
 that can last for multiple
 lines
 )test" + cpp2::to_string(i) + R"test( R"(this can be added too)"
-calculations like m["one"] + m["two"] = )test" + cpp2::to_string(cpp2::assert_in_bounds(m, "one") + cpp2::assert_in_bounds(m, "two")) + R"test( also works
+calculations like m["one"] + m["two"] = )test" + cpp2::to_string(CPP2_ASSERT_IN_BOUNDS(m, "one") + CPP2_ASSERT_IN_BOUNDS(m, "two")) + R"test( also works
 )test" + cpp2::to_string("at the beginning of the line") +  R"test(!!!)test"}; 
 
     std::string raw_str_inter_multi {R"(
@@ -50,6 +50,6 @@ calculations like m["one"] + m["two"] = )test" + cpp2::to_string(cpp2::assert_in
     std::cout << std::move(raw_str_multi) << std::endl;
     std::cout << std::move(raw_str_inter) << std::endl;
     std::cout << std::move(raw_str_inter_multi) << std::endl;
-    std::cout << (cpp2::to_string(cpp2::assert_in_bounds(m, "one")) + R"(.)" + cpp2::to_string(cpp2::assert_in_bounds(m, "two")) + R"(.)" + cpp2::to_string(cpp2::assert_in_bounds(std::move(m), "three")) + R"(.)" + cpp2::to_string(std::move(i))) << std::endl;
+    std::cout << (cpp2::to_string(CPP2_ASSERT_IN_BOUNDS(m, "one")) + R"(.)" + cpp2::to_string(CPP2_ASSERT_IN_BOUNDS(m, "two")) + R"(.)" + cpp2::to_string(CPP2_ASSERT_IN_BOUNDS(std::move(m), "three")) + R"(.)" + cpp2::to_string(std::move(i))) << std::endl;
 }
 

regression-tests/test-results/version

@@ -1,5 +1,5 @@
 
-cppfront compiler v0.3.0   Build 8B19:1018
+cppfront compiler v0.3.0   Build 8B20:1424
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0