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libstdc++: Fix ranges::copy_backward for a single memcpyable element [PR117121]

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The result iterator needs to be decremented before writing to it.

Improve the PR 108846 tests for all of std::copy, std::copy_n,
std::copy_backward, and the std::ranges versions.

libstdc++-v3/ChangeLog:

	PR libstdc++/117121
	* include/bits/ranges_algobase.h (copy_backward): Decrement
	output iterator before assigning one element through it.
	* testsuite/25_algorithms/copy/108846.cc: Ensure the algorithm's
	effects are correct for a single memcpyable element.
	* testsuite/25_algorithms/copy_backward/108846.cc: Likewise.
	* testsuite/25_algorithms/copy_n/108846.cc: Likewise.
This commit is contained in:
Jonathan Wakely 2024-10-13 19:14:04 +01:00 • committed by Jonathan Wakely
parent 2ef62aa1a3
commit 27f6b376e8
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4 changed files with 48 additions and 2 deletions
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5
libstdc++-v3/include/bits/ranges_algobase.h
View file

@ -418,12 +418,13 @@ namespace ranges
{
using _ValueTypeI = iter_value_t<_Iter>;
auto __num = __last - __first;
__result -= __num;
if (__num > 1) [[likely]]
__builtin_memmove(__result - __num, __first,
__builtin_memmove(__result, __first,
sizeof(_ValueTypeI) * __num);
else if (__num == 1)
ranges::__assign_one<_IsMove>(__first, __result);
return {__first + __num, __result - __num};
return {__first + __num, __result};
}
}

15
libstdc++-v3/testsuite/25_algorithms/copy/108846.cc
View file

@ -25,10 +25,15 @@ test_pr108846()
B *src = &dsrc;
// If this is optimized to memmove it will overwrite tail padding.
std::copy(src, src+1, dst);
// Check tail padding is unchanged:
VERIFY(ddst.x == 3);
// Check B subobject was copied:
VERIFY(ddst.i == 4 && ddst.j == 5);
#if __cpp_lib_ranges >= 201911L
ddst.i = ddst.j = 99;
std::ranges::copy(src, src+1, dst);
VERIFY(ddst.x == 3);
VERIFY(ddst.i == 4 && ddst.j == 5);
#endif
}
@ -52,10 +57,15 @@ test_non_const_copy_assign()
B2 *src = &dsrc;
// Ensure the not-taken trivial copy path works for this type.
std::copy(src, src+1, dst);
// Check tail padding is unchanged:
VERIFY(ddst.x == 3);
// Check B subobject was copied:
VERIFY(ddst.i == 4 && ddst.j == 5);
#if __cpp_lib_ranges >= 201911L
ddst.i = ddst.j = 99;
std::ranges::copy(src, src+1, dst);
VERIFY(ddst.x == 3);
VERIFY(ddst.i == 4 && ddst.j == 5);
#endif
}
@ -81,10 +91,15 @@ test_non_const_copy_assign_trivial()
B3 *src = &dsrc;
// If this is optimized to memmove it will overwrite tail padding.
std::copy(src, src+1, dst);
// Check tail padding is unchanged:
VERIFY(ddst.x == 3);
// Check B subobject was copied:
VERIFY(ddst.i == 4 && ddst.j == 5);
#if __cpp_lib_ranges >= 201911L
ddst.i = ddst.j = 99;
std::ranges::copy(src, src+1, dst);
VERIFY(ddst.x == 3);
VERIFY(ddst.i == 4 && ddst.j == 5);
#endif
}

15
libstdc++-v3/testsuite/25_algorithms/copy_backward/108846.cc
View file

@ -25,10 +25,15 @@ test_pr108846()
B *src = &dsrc;
// If this is optimized to memmove it will overwrite tail padding.
std::copy_backward(src, src+1, dst+1);
// Check tail padding is unchanged:
VERIFY(ddst.x == 3);
// Check B subobject was copied:
VERIFY(ddst.i == 4 && ddst.j == 5);
#if __cpp_lib_ranges >= 201911L
ddst.i = ddst.j = 99;
std::ranges::copy_backward(src, src+1, dst+1);
VERIFY(ddst.x == 3);
VERIFY(ddst.i == 4 && ddst.j == 5);
#endif
}
@ -52,10 +57,15 @@ test_non_const_copy_assign()
B2 *src = &dsrc;
// Ensure the not-taken trivial copy path works for this type.
std::copy_backward(src, src+1, dst+1);
// Check tail padding is unchanged:
VERIFY(ddst.x == 3);
// Check B subobject was copied:
VERIFY(ddst.i == 4 && ddst.j == 5);
#if __cpp_lib_ranges >= 201911L
ddst.i = ddst.j = 99;
std::ranges::copy_backward(src, src+1, dst+1);
VERIFY(ddst.x == 3);
VERIFY(ddst.i == 4 && ddst.j == 5);
#endif
}
@ -81,10 +91,15 @@ test_non_const_copy_assign_trivial()
B3 *src = &dsrc;
// If this is optimized to memmove it will overwrite tail padding.
std::copy_backward(src, src+1, dst+1);
// Check tail padding is unchanged:
VERIFY(ddst.x == 3);
// Check B subobject was copied:
VERIFY(ddst.i == 4 && ddst.j == 5);
#if __cpp_lib_ranges >= 201911L
ddst.i = ddst.j = 99;
std::ranges::copy_backward(src, src+1, dst+1);
VERIFY(ddst.x == 3);
VERIFY(ddst.i == 4 && ddst.j == 5);
#endif
}

15
libstdc++-v3/testsuite/25_algorithms/copy_n/108846.cc
View file

@ -25,10 +25,15 @@ test_pr108846()
B *src = &dsrc;
// If this is optimized to memmove it will overwrite tail padding.
std::copy_n(src, 1, dst);
// Check tail padding is unchanged:
VERIFY(ddst.x == 3);
// Check B subobject was copied:
VERIFY(ddst.i == 4 && ddst.j == 5);
#if __cpp_lib_ranges >= 201911L
ddst.i = ddst.j = 99;
std::ranges::copy_n(src, 1, dst);
VERIFY(ddst.x == 3);
VERIFY(ddst.i == 4 && ddst.j == 5);
#endif
}
@ -52,10 +57,15 @@ test_non_const_copy_assign()
B2 *src = &dsrc;
// Ensure the not-taken trivial copy path works for this type.
std::copy_n(src, 1, dst);
// Check tail padding is unchanged:
VERIFY(ddst.x == 3);
// Check B subobject was copied:
VERIFY(ddst.i == 4 && ddst.j == 5);
#if __cpp_lib_ranges >= 201911L
ddst.i = ddst.j = 99;
std::ranges::copy_n(src, 1, dst);
VERIFY(ddst.x == 3);
VERIFY(ddst.i == 4 && ddst.j == 5);
#endif
}
@ -79,10 +89,15 @@ test_non_const_copy_assign_trivial()
B3 *src = &dsrc;
// If this is optimized to memmove it will overwrite tail padding.
std::copy_n(src, 1, dst);
// Check tail padding is unchanged:
VERIFY(ddst.x == 3);
// Check B subobject was copied:
VERIFY(ddst.i == 4 && ddst.j == 5);
#if __cpp_lib_ranges >= 201911L
ddst.i = ddst.j = 99;
std::ranges::copy_n(src, 1, dst);
VERIFY(ddst.x == 3);
VERIFY(ddst.i == 4 && ddst.j == 5);
#endif
}