…ntroducing one-sided binary search for non-random iterators.

…dom iterators.

One-sided binary search, aka meta binary search, has been in the public domain for decades, and has the general
advantage of being Ω(1) rather than the classic algorithm's Ω(log(n)), with the downside of executing at most
2*log(n) comparisons vs the classic algorithm's exact log(n). There are two scenarios in which it really shines:
the first one is when operating over non-random iterators, because the classic algorithm requires knowing the
container's size upfront, which adds Ω(n) iterator increments to the complexity. The second one is when you're
traversing the container in order, trying to fast-forward to the next value: in that case, the classic algorithm
would yield Ω(n*log(n)) comparisons and, for non-random iterators, Ω(n^2) iterator increments, whereas the one-sided
version will yield O(n) operations on both counts, with a Ω(log(n)) bound on the number of comparisons.

… to introducing use of one-sided binary search to fast-forward over ranges of elements.

…omplexity of set_intersection.

…s before C++14

…elf since that violates the complexity guarantees from the standard.

… it down for faster runs, and including comparison counter.

…)` must start with `__step==0`, otherwise we can't match the complexity of linear search when continually matching (like a std::set_intersection() of matching containers will).

…d an environment variable so we can choose to either measure time more accurately or obtain more information.

This led me down an interesting road of validating benchmark results and finding a significant discrepancy in timings between when I run all test cases at once or `--benchmark-filter` them individually.

* main: (5908 commits)
  [readtapi] Cleanup printing command line options (llvm#75106)
  [flang] Fix compilation error due to variable no being used (llvm#75210)
  [C API] Add getters and setters for fast-math flags on relevant instructions (llvm#75123)
  [libc++][CI] Tests the no RTTI configuration. (llvm#65518)
  [RemoveDIs] Fold variable into assert, it's only used once. NFC
  [RemoveDI] Handle DPValues in SROA (llvm#74089)
  [AArch64][GlobalISel] Test Pre-Commit for Look into array's element
  [mlir][tensor] Fix bug in `tensor.extract(tensor.from_elements)` folder (llvm#75109)
  [analyzer] Move alpha checker EnumCastOutOfRange to optin (llvm#67157)
  [RemoveDIs] Handle DPValues in replaceDbgDeclare (llvm#73507)
  [SHT_LLVM_BB_ADDR_MAP] Implements PGOAnalysisMap in Object and ObjectYAML with tests.
  [X86][GlobalISel] Add instruction selection for G_SELECT (llvm#70753)
  [AMDGPU] Remove unused function splitScalar64BitAddSub
  [LLVM][DWARF] Add compilation directory and dwo name to TU in dwo section (llvm#74909)
  [clang][Interp] Implement __builtin_ffs (llvm#72988)
  [RemoveDIs] Update ConvertDebugDeclareToDebugValue after llvm#72276 (llvm#73508)
  [libc][NFC] Reuse `FloatProperties` constant instead of creating new ones (llvm#75187)
  [RemoveDIs] Fix removeRedundantDdbgInstrs utils for dbg.declares (llvm#74102)
  Reapply "[RemoveDIs][NFC] Find DPValues using findDbgDeclares  (llvm#73500)"
  [GitHub] Remove author association print from new-prs workflow
  ...

…or`"

This reverts commit 995d04b.

* Fix tests I had broken.
* More tweaks and better comments.

* llvm/main: (500 commits)
  [docs] Add beginner-focused office hours (llvm#80308)
  [mlir][sparse] external entry method wrapper for sparse tensors (llvm#80326)
  [StackSlotColoring] Ignore non-spill objects in RemoveDeadStores. (llvm#80242)
  [libc][stdbit] fix return types (llvm#80337)
  Revert "[RISCV] Refine cost on Min/Max reduction" (llvm#80340)
  [TTI]Add support for strided loads/stores.
  [analyzer][HTMLRewriter] Cache partial rewrite results. (llvm#80220)
  [flang][openacc][openmp] Use #0 from hlfir.declare value when generating bound ops (llvm#80317)
  [AArch64][PAC] Expand blend(reg, imm) operation in aarch64-pauth pass (llvm#74729)
  [SHT_LLVM_BB_ADDR_MAP][llvm-readobj] Implements llvm-readobj handling for PGOAnalysisMap. (llvm#79520)
  [libc] add bazel support for most of unistd (llvm#80078)
  [clang-tidy] Remove enforcement of rule C.48 from cppcoreguidelines-prefer-member-init (llvm#80330)
  [OpenMP] Fix typo (NFC) (llvm#80332)
  [BOLT] Enable re-writing of Linux kernel binary (llvm#80228)
  [BOLT] Adjust section sizes based on file offsets (llvm#80226)
  [libc] fix stdbit include test when not all entrypoints are available (llvm#80323)
  [RISCV][GISel] RegBank select and instruction select for vector G_ADD, G_SUB (llvm#74114)
  [RISCV] Add srmcfg CSR from Ssqosid extension. (llvm#79914)
  [mlir][sparse] add sparsification options to pretty print and debug s… (llvm#80205)
  [RISCV][MC] MC layer support for the experimental zalasr extension (llvm#79911)
  ...

* llvm/main: (328 commits)
  [Flang][OpenMP] Attempt to make map-types-and-sizes.f90 test more agnostic to other architectures
  [Transforms] Add more cos combinations to SimplifyLibCalls and InstCombine (llvm#79699)
  [workflows] Close issues used for backports once the PR has been created (llvm#80394)
  [RISCV] Add support for RISC-V Pointer Masking (llvm#79929)
  [lldb] Cleanup regex in libcxx formatters (NFC) (llvm#80618)
  [lldb] Remove unused private TypeCategoryMap methods (NFC) (llvm#80602)
  [mlir][sparse] refine sparse assembler strategy (llvm#80521)
  [NFC] Fix typo (llvm#80703)
  Fix broken ARM processor features test (llvm#80717)
  [ValueTracking][NFC] Pass `SimplifyQuery` to `computeKnownFPClass` family (llvm#80657)
  [x86_64][windows][swift] do not use Swift async extended frame for wi… (llvm#80468)
  [X86] addConstantComments - add FP16 MOVSH asm comments support
  [X86] Regenerate some vector constant comments missed in recent patches to improve mask predicate handling in addConstantComments
  [clang][AMDGPU][CUDA] Handle __builtin_printf for device printf (llvm#68515)
  Add some clarification to email check message
  [GitHub][Workflows] Prevent multiple private email comments (temporarily) (llvm#80648)
  [workflows] Use /mnt as the build directory on Linux (llvm#80583)
  [Flang][OpenMP] Initial mapping of Fortran pointers and allocatables for target devices (llvm#71766)
  [AMDGPU] GlobalISel for f8 conversions (llvm#80503)
  [AMDGPU] Fixed byte_sel of v_cvt_f32_bf8/v_cvt_f32_fp8 (llvm#80502)
  ...

…s of the method.

…pp` is ok on gcc.

…mplexity validation.

* llvm/main: (7814 commits)
  [libc++] Add some private headers to libcxx.imp (llvm#89568)
  [Frontend][OpenMP] Add functions for checking construct type (llvm#87258)
  AtomicExpand: Emit or with constant on RHS
  [VPlan] Ignore incoming values with constant false mask. (llvm#89384)
  [Clang][Parser] Don't always destroy template annotations at the end of a declaration (llvm#89494)
  [X86] getTargetShuffleMask - update to take a SDValue instead of a SDNode. NFC.
  [DAGCombiner] Fix miscompile bug in combineShiftOfShiftedLogic (llvm#89616)
  [DAGCombiner] Pre-commit test case for miscompile bug in combineShiftOfShiftedLogic
  [Flang][OpenMP] Add restriction about subobjects to firstprivate and … (llvm#89608)
  [SelectionDAG] Mark frame index as "aliased" at argument copy elison (llvm#89712)
  Pre-commit reproducer for argument copy elison related bug
  [InstCombine] Fold fcmp into select (llvm#86482)
  Make default initialization explicit
  [clang-tidy] Avoid overflow when dumping unsigned integer values (llvm#85060)
  [ARM][AArch64] Split out processor and feature tablegen defs [NFC] (llvm#88282)
  [TableGen] Fix ReplaceRegAction RTTI Kind
  [VectorCombine] foldShuffleOfShuffles - add missing arguments to getShuffleCost calls.
  [VPlan] Skip extending ICmp results in trunateToMinimalBitwidth.
  [LLVM][CodeGen][SVE] rev(whilelo(a,b)) -> whilehi(b,a). (llvm#88294)
  RenameIndependentSubregs: Add missing sub-range for new IMPLICIT_DEFs (llvm#89050)
  ...

…hoice of not having a `default` case in `switch`.

…the function closer to its point of usage and document what `genCacheUnfriendlyData()` is trying to do in its own comment. `getVectorOfRandom()` has imho a good name which describes all it's meant to achieve, it's `genCacheUnfriendlyData()` that needs explaining.

…ut it would be good to be sure that we have a good baseline after this big merge from main.

… function -- make it a lambda, to avoid the explicit template parameter a freestanding function would require.

… benchmark.

…ce_to` -- no reason IMO to have a second override if `__advance_to = ranges::advance` in c++20...

…` instead of a templated `_Distance` in `_IterOps::__advance_to()`

…ce qualification, insufficient comments, and direct use of iterator traits.

…h a function. I think I managed to preserve readability by keeping `__add_output_unless()` as a lambda.

…tion_add_output_unless()`, because the lambda [tripped the "MacOS with C++03" test run](https://buildkite.com/llvm-project/libcxx-ci/builds/35055#018f173c-f155-4fbb-b6d7-a7aba01cec9e):

```
```

…cy in `__set_intersection()` base overload.

… generation stage, time won't be measured before we go into the benchmark::State loops.

@ldionne's latest inline review suggestions.

Co-authored-by: Louis Dionne <[email protected]>

… to its pre-existing sibling and remove leftover comments.

…unts/counted_set_intersection/', and split complexity tests into `set_intersection_complexity.pass.cpp`.

… `std::set_intersection()`

…rantees for a single match over an input of 1 to 20 elements.

…dening mode inside `testComplexityBasic()` as well.

…ething better after some more thinking...

* s/__set_intersection_add_output_unless/__set_intersection_add_output_if_equal/
* Add comments to explain the logic for equality comparison

* llvm/main: (8718 commits)
  [LLVM] Add `llvm.experimental.vector.compress` intrinsic (llvm#92289)
  [Clang] [C23] Implement N2653: u8 strings are char8_t[] (llvm#97208)
  [SLP][REVEC] Make SLP support revectorization (-slp-revec) and add simple test. (llvm#98269)
  [Flang] Exclude the reference to TIME_UTC for AIX. (llvm#99069)
  [clang][Sema] Improve `Sema::CheckCXXDefaultArguments` (llvm#97338)
  adjust the Xtensa backend after change f270a4d
  [lldb][Bazel]: Second attempt to adapt for a751f65
  Revert "[lldb][Bazel]: Adapt BUILD.bazel file for a751f65"
  [lldb][Bazel]: Adapt BUILD.bazel file for a751f65
  [emacs] Fix autoloading for llvm-mir-mode (llvm#98984)
  [SLP]Improve minbitwidth analysis for trun'ed gather nodes.
  [Clang][Concepts] Avoid substituting into constraints for invalid TemplateDecls (llvm#75697)
  [LV][NFC]Introduce isScalableVectorizationAllowed() to refactor getMaxLegalScalableVF().
  Revert "[AArch64] Remove superfluous sxtw in peephole opt (llvm#96293)"
  [AArch64][GISel] Add test cases for folding shifts into load/store addressing modes (NFC)
  [LV] Process dead interleave pointer ops in reverse order.
  [AMDGPU] Remove SIWholeQuadMode pass early exit (llvm#98450)
  [InstrRef][NFC] Avoid un-necessary DenseMap queries (llvm#99048)
  [gn build] Port e94e72a
  [LV][AArch64] Prefer Fixed over Scalable if cost-model is equal (Neoverse V2) (llvm#95819)
  ...