[libcxx] Optimize std::generate for segmented iterators #163006
Merged
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
llvmbot
added
the
libc++
|
@llvm/pr-subscribers-libcxx Author: Connector Switch (c8ef) ChangesPart of #102817. Full diff: https://github.com/llvm/llvm-project/pull/163006.diff 2 Files Affected:
diff --git a/libcxx/include/__algorithm/generate.h b/libcxx/include/__algorithm/generate.h
index c95b527402f5d..91e2ada7daf77 100644
--- a/libcxx/include/__algorithm/generate.h
+++ b/libcxx/include/__algorithm/generate.h
@@ -9,7 +9,10 @@
#ifndef _LIBCPP___ALGORITHM_GENERATE_H
#define _LIBCPP___ALGORITHM_GENERATE_H
+#include <__algorithm/for_each_segment.h>
#include <__config>
+#include <__iterator/segmented_iterator.h>
+#include <__type_traits/enable_if.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
@@ -17,13 +20,33 @@
_LIBCPP_BEGIN_NAMESPACE_STD
-template <class _ForwardIterator, class _Generator>
+template <class _ForwardIterator, class _Sent, class _Generator>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
-generate(_ForwardIterator __first, _ForwardIterator __last, _Generator __gen) {
+__generate(_ForwardIterator __first, _Sent __last, _Generator __gen) {
for (; __first != __last; ++__first)
*__first = __gen();
}
+#ifndef _LIBCPP_CXX03_LANG
+template <class _SegmentedIterator,
+ class _Generator,
+ __enable_if_t<__is_segmented_iterator_v<_SegmentedIterator>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
+_SegmentedIterator __generate(_SegmentedIterator __first, _SegmentedIterator __last, _Generator& __gen) {
+ using __local_iterator_t = typename __segmented_iterator_traits<_SegmentedIterator>::__local_iterator;
+ std::__for_each_segment(__first, __last, [&](__local_iterator_t __lfirst, __local_iterator_t __llast) {
+ std::__generate(__lfirst, __llast, __gen);
+ });
+ return __last;
+}
+#endif // !_LIBCPP_CXX03_LANG
+
+template <class _ForwardIterator, class _Generator>
+inline _LIBCPP_HIDE_FROM_ABI
+_LIBCPP_CONSTEXPR_SINCE_CXX20 void generate(_ForwardIterator __first, _ForwardIterator __last, _Generator __gen) {
+ std::__generate(__first, __last, __gen);
+}
+
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___ALGORITHM_GENERATE_H
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.generate/generate.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.generate/generate.pass.cpp
index 29d32d7156742..4591d7ece4645 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.generate/generate.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.generate/generate.pass.cpp
@@ -16,6 +16,7 @@
#include <algorithm>
#include <cassert>
+#include <deque>
#include "test_macros.h"
#include "test_iterators.h"
@@ -51,12 +52,22 @@ test()
assert(ia[3] == 1);
}
+void deque_test() {
+ int sizes[] = {0, 1, 2, 1023, 1024, 1025, 2047, 2048, 2049};
+ for (const int size : sizes) {
+ std::deque<int> d(size);
+ std::generate(d.begin(), d.end(), gen_test());
+ assert(std::all_of(d.begin(), d.end(), [](int x) { return x == 1; }));
+ }
+}
+
int main(int, char**)
{
test<forward_iterator<int*> >();
test<bidirectional_iterator<int*> >();
test<random_access_iterator<int*> >();
test<int*>();
+ deque_test();
#if TEST_STD_VER > 17
static_assert(test_constexpr());
|
philnik777
reviewed
Oct 13, 2025
You mean like following? template<class ForwardIt, class Generator>
void generate(ForwardIt first, ForwardIt last, Generator gen) {
std::for_each(first, last, [&gen](auto& element) {
element = gen();
});
}Will test this tonight. |
|
To some extent, I think the current implementation is also acceptable since it uses the for_each_segment utility. |
Forwarding this to template <class _ForwardIterator, class _Generator>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
generate(_ForwardIterator __first, _ForwardIterator __last, _Generator __gen) {
std::for_each(__first, __last, [&](auto& __element) { __element = __gen(); });
} |
|
Have you enabled optimizations? |
It seems that the default |
|
This looks weird... |
|
While both implementations offer the same performance, the for_each forward approach cannot properly build the benchmark, failing specifically on regex testing. It's odd because locally, using @philnik777 Could you please help take a look? |
|
This usually indicates that your code doesn't work in C++14 mode. You should try to run lit with e.g. |
I still haven't figured out why the regex check failed, but one of the test error message is above. I suspect it relates to std::__invoke. Is it possible to revert to the original version without forwarding to std::for_each? |
|
It's really weird that the regex check still isn't working. Even worse, it isn't producing a CMakeError log that I can use to reproduce the failed compilation. I ran the full test suite and found that the failures are only related to fs(symlink), iostream, and locale, which seems to have little relevance to std::generator. |
|
I also checked the GitHub Actions CMakeError log for the REGEX, but it didn't return any hit. |
|
Get a clang ICE on c++11 mode: https://godbolt.org/z/P4j6r5cra 😆 |
|
I think I prefer the functor approach to make sure it works. |
|
The windows arm mingw CI failure seems unrelated. |
libcxx/test/std/algorithms/alg.modifying.operations/alg.generate/generate.pass.cpp
Show resolved
Hide resolved
philnik777
reviewed
Oct 17, 2025
Co-authored-by: A. Jiang <[email protected]>
frederick-vs-ja
approved these changes
Oct 20, 2025
|
Thanks for the valuable feedback! |
philnik777
pushed a commit
that referenced
this pull request
Oct 21, 2025
Part of #102817. This is a natural follow-up to #163006. We are forwarding `std::generate_n` to `std::__for_each_n` (`std::for_each_n` needs c++17), resulting in improved performance for segmented iterators. before: ``` std::generate_n(deque<int>)/32 17.5 ns 17.3 ns 40727273 std::generate_n(deque<int>)/50 25.7 ns 25.5 ns 26352941 std::generate_n(deque<int>)/1024 490 ns 487 ns 1445161 std::generate_n(deque<int>)/8192 3908 ns 3924 ns 179200 ``` after: ``` std::generate_n(deque<int>)/32 11.1 ns 11.0 ns 64000000 std::generate_n(deque<int>)/50 16.1 ns 16.0 ns 44800000 std::generate_n(deque<int>)/1024 291 ns 292 ns 2357895 std::generate_n(deque<int>)/8192 2269 ns 2250 ns 298667 ```
ronlieb
added a commit
to ROCm/llvm-project
that referenced
this pull request
Oct 21, 2025
* [flang] Fix standalone build regression from llvm#161179 (llvm#164309) Fix incorrect linking and dependencies introduced in llvm#161179 that break standalone builds of Flang. Signed-off-by: Michał Górny <[email protected]> * [AMDGPU] Remove magic constants from V_PK_ADD_F32 pattern. NFC (llvm#164335) * [AMDGPU] Update code sequence for CU-mode Release Fences in GFX10+ (llvm#161638) They were previously optimized to not emit any waitcnt, which is technically correct because there is no reordering of operations at workgroup scope in CU mode for GFX10+. This breaks transitivity however, for example if we have the following sequence of events in one thread: - some stores - store atomic release syncscope("workgroup") - barrier then another thread follows with - barrier - load atomic acquire - store atomic release syncscope("agent") It does not work because, while the other thread sees the stores, it cannot release them at the wider scope. Our release fences aren't strong enough to "wait" on stores from other waves. We also cannot strengthen our release fences any further to allow for releasing other wave's stores because only GFX12 can do that with `global_wb`. GFX10-11 do not have the writeback instruction. It'd also add yet another level of complexity to code sequences, with both acquire/release having CU-mode only alternatives. Lastly, acq/rel are always used together. The price for synchronization has to be paid either at the acq, or the rel. Strengthening the releases would just make the memory model more complex but wouldn't help performance. So the choice here is to streamline the code sequences by making CU and WGP mode emit almost identical (vL0 inv is not needed in CU mode) code for release (or stronger) atomic ordering. This also removes the `vm_vsrc(0)` wait before barriers. Now that the release fence in CU mode is strong enough, it is no longer needed. Supersedes llvm#160501 Solves SC1-6454 * [InstSimplify] Support ptrtoaddr in simplifyGEPInst() (llvm#164262) This adds support for ptrtoaddr in the `ptradd p, ptrtoaddr(p2) - ptrtoaddr(p) -> p2` fold. This fold requires that p and p2 have the same underlying object (otherwise the provenance may not be the same). The argument I would like to make here is that because the underlying objects are the same (and the pointers in the same address space), the non-address bits of the pointer must be the same. Looking at some specific cases of underlying object relationship: * phi/select: Trivially true. * getelementptr: Only modifies address bits, non-address bits must remain the same. * addrspacecast round-trip cast: Must preserve all bits because we optimize such round-trip casts away. * non-interposable global alias: I'm a bit unsure about this one, but I guess the alias and the aliasee must have the same non-address bits? * various intrinsics like launder.invariant.group, ptrmask. I think these all either preserve all pointer bits (like the invariant.group ones) or at least the non-address bits (like ptrmask). There are some interesting cases like amdgcn.make.buffer.rsrc, but those are cross address-space. ----- There is a second `gep (gep p, C), (sub 0, ptrtoint(p)) -> C` transform in this function, which I am not extending to handle ptrtoaddr, adding negative tests instead. This transform is overall dubious for provenance reasons, but especially dubious with ptrtoaddr, as then we don't have the guarantee that provenance of `p` has been exposed. * [Hexagon] Add REQUIRES: asserts to test This test uses -debug-only, so needs an assertion-enabled build. * [AArch64] Combing scalar_to_reg into DUP if the DUP already exists (llvm#160499) If we already have a dup(x) as part of the DAG along with a scalar_to_vec(x), we can re-use the result of the dup to the scalar_to_vec(x). * [CAS] OnDiskGraphDB - fix MSVC "not all control paths return a value" warnings. NFC. (llvm#164369) * Reapply "[libc++] Optimize __hash_table::erase(iterator, iterator)" (llvm#162850) This reapplication fixes the use after free caused by not properly updating the bucket list in one case. Original commit message: Instead of just calling the single element `erase` on every element of the range, we can combine some of the operations in a custom implementation. Specifically, we don't need to search for the previous node or re-link the list every iteration. Removing this unnecessary work results in some nice performance improvements: ``` ----------------------------------------------------------------------------------------------------------------------- Benchmark old new ----------------------------------------------------------------------------------------------------------------------- std::unordered_set<int>::erase(iterator, iterator) (erase half the container)/0 457 ns 459 ns std::unordered_set<int>::erase(iterator, iterator) (erase half the container)/32 995 ns 626 ns std::unordered_set<int>::erase(iterator, iterator) (erase half the container)/1024 18196 ns 7995 ns std::unordered_set<int>::erase(iterator, iterator) (erase half the container)/8192 124722 ns 70125 ns std::unordered_set<std::string>::erase(iterator, iterator) (erase half the container)/0 456 ns 461 ns std::unordered_set<std::string>::erase(iterator, iterator) (erase half the container)/32 1183 ns 769 ns std::unordered_set<std::string>::erase(iterator, iterator) (erase half the container)/1024 27827 ns 18614 ns std::unordered_set<std::string>::erase(iterator, iterator) (erase half the container)/8192 266681 ns 226107 ns std::unordered_map<int, int>::erase(iterator, iterator) (erase half the container)/0 455 ns 462 ns std::unordered_map<int, int>::erase(iterator, iterator) (erase half the container)/32 996 ns 659 ns std::unordered_map<int, int>::erase(iterator, iterator) (erase half the container)/1024 15963 ns 8108 ns std::unordered_map<int, int>::erase(iterator, iterator) (erase half the container)/8192 136493 ns 71848 ns std::unordered_multiset<int>::erase(iterator, iterator) (erase half the container)/0 454 ns 455 ns std::unordered_multiset<int>::erase(iterator, iterator) (erase half the container)/32 985 ns 703 ns std::unordered_multiset<int>::erase(iterator, iterator) (erase half the container)/1024 16277 ns 9085 ns std::unordered_multiset<int>::erase(iterator, iterator) (erase half the container)/8192 125736 ns 82710 ns std::unordered_multimap<int, int>::erase(iterator, iterator) (erase half the container)/0 457 ns 454 ns std::unordered_multimap<int, int>::erase(iterator, iterator) (erase half the container)/32 1091 ns 646 ns std::unordered_multimap<int, int>::erase(iterator, iterator) (erase half the container)/1024 17784 ns 7664 ns std::unordered_multimap<int, int>::erase(iterator, iterator) (erase half the container)/8192 127098 ns 72806 ns ``` This reverts commit acc3a62. * [TableGen] List the indices of sub-operands (llvm#163723) Some instances of the `Operand` class used in Tablegen instruction definitions expand to a cluster of multiple operands at the MC layer, such as complex addressing modes involving base + offset + shift, or clusters of operands describing conditional Arm instructions or predicated MVE instructions. There's currently no convenient way for C++ code to know the offset of one of those sub-operands from the start of the cluster: instead it just hard-codes magic numbers like `index+2`, which is hard to read and fragile. This patch adds an extra piece of output to `InstrInfoEmitter` to define those instruction offsets, based on the name of the `Operand` class instance in Tablegen, and the names assigned to the sub-operands in the `MIOperandInfo` field. For example, if target Foo were to define def Bar : Operand { let MIOperandInfo = (ops GPR:$first, i32imm:$second); // ... } then the new constants would be `Foo::SUBOP_Bar_first` and `Foo::SUBOP_Bar_second`, defined as 0 and 1 respectively. As an example, I've converted some magic numbers related to the MVE predication operand types (`vpred_n` and its superset `vpred_r`) to use the new named constants in place of the integer literals they previously used. This is more verbose, but also clearer, because it explains why the integer is chosen instead of what its value is. * [lldb] Add bidirectional packetLog to gdbclientutils.py (llvm#162176) While debugging the tests for llvm#155000 I found it helpful to have both sides of the simulated gdb-rsp traffic rather than just the responses so I've extended the packetLog in MockGDBServerResponder to record traffic in both directions. Tests have been updated accordingly * [MLIR] [Vector] Added canonicalizer for folding from_elements + transpose (llvm#161841) ## Description Adds a new canonicalizer that folds `vector.from_elements(vector.transpose))` => `vector.from_elements`. This canonicalization reorders the input elements for `vector.from_elements`, adjusts the output shape to match the effect of the transpose op and eliminating its need. ## Testing Added a 2D vector lit test that verifies the working of the rewrite. --------- Signed-off-by: Keshav Vinayak Jha <[email protected]> * [DA] Add initial support for monotonicity check (llvm#162280) The dependence testing functions in DA assume that the analyzed AddRec does not wrap over the entire iteration space. For AddRecs that may wrap, DA should conservatively return unknown dependence. However, no validation is currently performed to ensure that this condition holds, which can lead to incorrect results in some cases. This patch introduces the notion of *monotonicity* and a validation logic to check whether a SCEV is monotonic. The monotonicity check classifies the SCEV into one of the following categories: - Unknown: Nothing is known about the monotonicity of the SCEV. - Invariant: The SCEV is loop-invariant. - MultivariateSignedMonotonic: The SCEV doesn't wrap in a signed sense for any iteration of the loops in the loop nest. The current validation logic basically searches an affine AddRec recursively and checks whether the `nsw` flag is present. Notably, it is still unclear whether we should also have a category for unsigned monotonicity. The monotonicity check is still under development and disabled by default for now. Since such a check is necessary to make DA sound, it should be enabled by default once the functionality is sufficient. Split off from llvm#154527. * [VPlan] Use VPlan::getRegion to shorten code (NFC) (llvm#164287) * [VPlan] Improve code using m_APInt (NFC) (llvm#161683) * [SystemZ] Avoid trunc(add(X,X)) patterns (llvm#164378) Replace with trunc(add(X,Y)) to avoid premature folding in upcoming patch llvm#164227 * [clang][CodeGen] Emit `llvm.tbaa.errno` metadata during module creation Let Clang emit `llvm.tbaa.errno` metadata in order to let LLVM carry out optimizations around errno-writing libcalls to, as long as it is proved the involved memory location does not alias `errno`. Previous discussion: https://discourse.llvm.org/t/rfc-modelling-errno-memory-effects/82972. * [LV][NFC] Remove undef from phi incoming values (llvm#163762) Split off from PR llvm#163525, this standalone patch replaces use of undef as incoming PHI values with zero, in order to reduce the likelihood of contributors hitting the `undef deprecator` warning in github. * [DA] Add option to enable specific dependence test only (llvm#164245) PR llvm#157084 added an option `da-run-siv-routines-only` to run only SIV routines in DA. This PR replaces that option with a more fine-grained one that allows to select other than SIV routines as well. This option is useful for regression testing of individual DA routines. This patch also reorganizes regression tests that use `da-run-siv-routines-only`. * [libcxx] Optimize `std::generate_n` for segmented iterators (llvm#164266) Part of llvm#102817. This is a natural follow-up to llvm#163006. We are forwarding `std::generate_n` to `std::__for_each_n` (`std::for_each_n` needs c++17), resulting in improved performance for segmented iterators. before: ``` std::generate_n(deque<int>)/32 17.5 ns 17.3 ns 40727273 std::generate_n(deque<int>)/50 25.7 ns 25.5 ns 26352941 std::generate_n(deque<int>)/1024 490 ns 487 ns 1445161 std::generate_n(deque<int>)/8192 3908 ns 3924 ns 179200 ``` after: ``` std::generate_n(deque<int>)/32 11.1 ns 11.0 ns 64000000 std::generate_n(deque<int>)/50 16.1 ns 16.0 ns 44800000 std::generate_n(deque<int>)/1024 291 ns 292 ns 2357895 std::generate_n(deque<int>)/8192 2269 ns 2250 ns 298667 ``` * [BOLT] Check entry point address is not in constant island (llvm#163418) There are cases where `addEntryPointAtOffset` is called with a given `Offset` that points to an address within a constant island. This triggers `assert(!isInConstantIsland(EntryPointAddress)` and causes BOLT to crash. This patch adds a check which ignores functions that would add such entry points and warns the user. * [llvm][dwarfdump] Pretty-print DW_AT_language_version (llvm#164222) In both verbose and non-verbose mode we will now use the `llvm::dwarf::LanguageDescription` to turn the version into a human readable string. In verbose mode we also display the raw version code (similar to how we display addresses in verbose mode). To make the version code and prettified easier to distinguish, we print the prettified name in colour (if available), which is consistent with how `DW_AT_language` is printed in colour. Before: ``` 0x0000000c: DW_TAG_compile_unit DW_AT_language_name (DW_LNAME_C) DW_AT_language_version (201112) ``` After: ``` 0x0000000c: DW_TAG_compile_unit DW_AT_language_name (DW_LNAME_C) DW_AT_language_version (201112 C11) ``` --------- Signed-off-by: Michał Górny <[email protected]> Signed-off-by: Keshav Vinayak Jha <[email protected]> Co-authored-by: Michał Górny <[email protected]> Co-authored-by: Stanislav Mekhanoshin <[email protected]> Co-authored-by: Pierre van Houtryve <[email protected]> Co-authored-by: Nikita Popov <[email protected]> Co-authored-by: David Green <[email protected]> Co-authored-by: Simon Pilgrim <[email protected]> Co-authored-by: Nikolas Klauser <[email protected]> Co-authored-by: Simon Tatham <[email protected]> Co-authored-by: Daniel Sanders <[email protected]> Co-authored-by: Keshav Vinayak Jha <[email protected]> Co-authored-by: Ryotaro Kasuga <[email protected]> Co-authored-by: Ramkumar Ramachandra <[email protected]> Co-authored-by: Antonio Frighetto <[email protected]> Co-authored-by: David Sherwood <[email protected]> Co-authored-by: Connector Switch <[email protected]> Co-authored-by: Asher Dobrescu <[email protected]> Co-authored-by: Michael Buch <[email protected]>
Lukacma
pushed a commit
to Lukacma/llvm-project
that referenced
this pull request
Oct 29, 2025
Part of llvm#102817. This patch attempts to optimize the performance of `std::generate` for segmented iterators. Below are the benchmark numbers from `libcxx\test\benchmarks\algorithms\modifying\generate.bench.cpp`. Test cases that use segmented iterators have also been added. - before ``` std::generate(deque<int>)/32 194 ns 193 ns 3733333 std::generate(deque<int>)/50 276 ns 276 ns 2488889 std::generate(deque<int>)/1024 5096 ns 5022 ns 112000 std::generate(deque<int>)/8192 40806 ns 40806 ns 17231 ``` - after ``` std::generate(deque<int>)/32 106 ns 105 ns 6400000 std::generate(deque<int>)/50 139 ns 138 ns 4977778 std::generate(deque<int>)/1024 2713 ns 2699 ns 248889 std::generate(deque<int>)/8192 18983 ns 19252 ns 37333 ``` --------- Co-authored-by: A. Jiang <[email protected]>
Lukacma
pushed a commit
to Lukacma/llvm-project
that referenced
this pull request
Oct 29, 2025
) Part of llvm#102817. This is a natural follow-up to llvm#163006. We are forwarding `std::generate_n` to `std::__for_each_n` (`std::for_each_n` needs c++17), resulting in improved performance for segmented iterators. before: ``` std::generate_n(deque<int>)/32 17.5 ns 17.3 ns 40727273 std::generate_n(deque<int>)/50 25.7 ns 25.5 ns 26352941 std::generate_n(deque<int>)/1024 490 ns 487 ns 1445161 std::generate_n(deque<int>)/8192 3908 ns 3924 ns 179200 ``` after: ``` std::generate_n(deque<int>)/32 11.1 ns 11.0 ns 64000000 std::generate_n(deque<int>)/50 16.1 ns 16.0 ns 44800000 std::generate_n(deque<int>)/1024 291 ns 292 ns 2357895 std::generate_n(deque<int>)/8192 2269 ns 2250 ns 298667 ```
aokblast
pushed a commit
to aokblast/llvm-project
that referenced
this pull request
Oct 30, 2025
Part of llvm#102817. This patch attempts to optimize the performance of `std::generate` for segmented iterators. Below are the benchmark numbers from `libcxx\test\benchmarks\algorithms\modifying\generate.bench.cpp`. Test cases that use segmented iterators have also been added. - before ``` std::generate(deque<int>)/32 194 ns 193 ns 3733333 std::generate(deque<int>)/50 276 ns 276 ns 2488889 std::generate(deque<int>)/1024 5096 ns 5022 ns 112000 std::generate(deque<int>)/8192 40806 ns 40806 ns 17231 ``` - after ``` std::generate(deque<int>)/32 106 ns 105 ns 6400000 std::generate(deque<int>)/50 139 ns 138 ns 4977778 std::generate(deque<int>)/1024 2713 ns 2699 ns 248889 std::generate(deque<int>)/8192 18983 ns 19252 ns 37333 ``` --------- Co-authored-by: A. Jiang <[email protected]>
aokblast
pushed a commit
to aokblast/llvm-project
that referenced
this pull request
Oct 30, 2025
) Part of llvm#102817. This is a natural follow-up to llvm#163006. We are forwarding `std::generate_n` to `std::__for_each_n` (`std::for_each_n` needs c++17), resulting in improved performance for segmented iterators. before: ``` std::generate_n(deque<int>)/32 17.5 ns 17.3 ns 40727273 std::generate_n(deque<int>)/50 25.7 ns 25.5 ns 26352941 std::generate_n(deque<int>)/1024 490 ns 487 ns 1445161 std::generate_n(deque<int>)/8192 3908 ns 3924 ns 179200 ``` after: ``` std::generate_n(deque<int>)/32 11.1 ns 11.0 ns 64000000 std::generate_n(deque<int>)/50 16.1 ns 16.0 ns 44800000 std::generate_n(deque<int>)/1024 291 ns 292 ns 2357895 std::generate_n(deque<int>)/8192 2269 ns 2250 ns 298667 ```
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
4 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Part of #102817.
This patch attempts to optimize the performance of
std::generatefor segmented iterators. Below are the benchmark numbers fromlibcxx\test\benchmarks\algorithms\modifying\generate.bench.cpp. Test cases that use segmented iterators have also been added.