Author: Mark de Wever
Date: 2024-05-09T18:39:08+02:00
New Revision: 937643b8e1017ce6456de0c05b1673bd9ed0800d
URL: https://github.com/llvm/llvm-project/commit/937643b8e1017ce6456de0c05b1673bd9ed0800d
DIFF: https://github.com/llvm/llvm-project/commit/937643b8e1017ce6456de0c05b1673bd9ed0800d.diff
LOG: [libc++][test] Fixes constexpr char_traits. (#90981)
The issue in nasty_char_traits was discovered by @StephanTLavavej who
provided
the solution they use in MSVC STL. This solution is based on that
example.
The same issue affects the constexpr_char_traits which was discovered in
https://github.com/llvm/llvm-project/pull/88389. This uses the same fix.
Fixes: https://github.com/llvm/llvm-project/issues/74221
Added:
Modified:
libcxx/test/support/constexpr_char_traits.h
libcxx/test/support/nasty_string.h
Removed:
################################################################################
diff --git a/libcxx/test/support/constexpr_char_traits.h b/libcxx/test/support/constexpr_char_traits.h
index 75380d5a7ffbb..7c487c504af13 100644
--- a/libcxx/test/support/constexpr_char_traits.h
+++ b/libcxx/test/support/constexpr_char_traits.h
@@ -16,6 +16,31 @@
#include "test_macros.h"
+// Tests whether the pointer p is in the range [first, last).
+//
+// Precondition: The range [first, last) is a valid range.
+//
+// Typically the pointers are compared with less than. This is not allowed when
+// the pointers belong to
diff erent ranges, which is UB. Typically, this is
+// benign at run-time, however since UB is not allowed during constant
+// evaluation this does not compile. This function does the validation without
+// UB.
+//
+// When p is in the range [first, last) the data can be copied from the
+// beginning to the end. Otherwise it needs to be copied from the end to the
+// beginning.
+template <class CharT>
+TEST_CONSTEXPR_CXX14 bool is_pointer_in_range(const CharT* first, const CharT* last, const CharT* p) {
+ if (first == p) // Needed when n == 0
+ return true;
+
+ for (; first != last; ++first)
+ if (first == p)
+ return true;
+
+ return false;
+}
+
template <class CharT>
struct constexpr_char_traits
{
@@ -98,23 +123,21 @@ constexpr_char_traits<CharT>::find(const char_type* s, std::size_t n, const char
}
template <class CharT>
-TEST_CONSTEXPR_CXX14 CharT*
-constexpr_char_traits<CharT>::move(char_type* s1, const char_type* s2, std::size_t n)
-{
- char_type* r = s1;
- if (s1 < s2)
- {
- for (; n; --n, ++s1, ++s2)
- assign(*s1, *s2);
- }
- else if (s2 < s1)
- {
- s1 += n;
- s2 += n;
- for (; n; --n)
- assign(*--s1, *--s2);
- }
- return r;
+TEST_CONSTEXPR_CXX14 CharT* constexpr_char_traits<CharT>::move(char_type* s1, const char_type* s2, std::size_t n) {
+ if (s1 == s2)
+ return s1;
+
+ char_type* r = s1;
+ if (is_pointer_in_range(s1, s1 + n, s2)) {
+ for (; n; --n)
+ assign(*s1++, *s2++);
+ } else {
+ s1 += n;
+ s2 += n;
+ for (; n; --n)
+ assign(*--s1, *--s2);
+ }
+ return r;
}
template <class CharT>
diff --git a/libcxx/test/support/nasty_string.h b/libcxx/test/support/nasty_string.h
index 672c3cb4ed9ea..ea9d83ccf282a 100644
--- a/libcxx/test/support/nasty_string.h
+++ b/libcxx/test/support/nasty_string.h
@@ -16,6 +16,7 @@
#include "make_string.h"
#include "test_macros.h"
+#include "constexpr_char_traits.h" // is_pointer_in_range
// This defines a nasty_string similar to nasty_containers. This string's
// value_type does operator hijacking, which allows us to ensure that the
@@ -118,11 +119,14 @@ constexpr const nasty_char* nasty_char_traits::find(const nasty_char* s, std::si
}
constexpr nasty_char* nasty_char_traits::move(nasty_char* s1, const nasty_char* s2, std::size_t n) {
+ if (s1 == s2)
+ return s1;
+
nasty_char* r = s1;
- if (s1 < s2) {
- for (; n; --n, ++s1, ++s2)
- assign(*s1, *s2);
- } else if (s2 < s1) {
+ if (is_pointer_in_range(s1, s1 + n, s2)) {
+ for (; n; --n)
+ assign(*s1++, *s2++);
+ } else {
s1 += n;
s2 += n;
for (; n; --n)