Identified with modernize-use-override.

Identified with readability-redundant-control-flow.

Identified with modernize-use-nullptr.

Identified with llvm-header-guard.

This adds a merge operand to all of the binary _VL nodes. Including
integer and widening. They all share multiclasses in tablegen
so doing them all at once was easiest.

I plan to use FADD_VL in an upcoming patch. The rest are just for
consistency to keep tablegen working.

This does reduce the isel table size by about 25k so that's nice.

Reviewed By: reames

Differential Revision: https://reviews.llvm.org/D130816

Based on review feedback from D130816.

Noticed by inspection and I can't seem to make a test case, but SSE arithmetic bit shifts clamp to the max shift amount (i.e. create a sign splat) - combineVectorShiftImm already does something similar.

This patch fixes the error llvm/lib/CodeGen/MachineScheduler.cpp(755): error C2065: 'MISchedCutoff': undeclared identifier in case of NDEBUG and LLVM_ENABLE_ABI_BREAKING_CHECKS.
Note MISchedCutoff is declared under #ifndef NDEBUG.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D130425

https://alive2.llvm.org/ce/z/vBNiiM

This matches variants of patterns that were folded with:
b5a9361c

warning: '\returns' command used in a comment that is attached to a function returning void

[X86] combineSelect fold 'smin' style pattern select(pcmpgt(RHS, LHS), LHS, RHS) -> select(pcmpgt(LHS, RHS), RHS, LHS) if pcmpgt(LHS, RHS) already exists

Avoids repeated commuted comparisons when we're performing min/max and clamp patterns

Follow-up to d4940c0f to further limit the transform
to avoid an unintended pattern/fold of a constant expression.

Differential Revision: https://reviews.llvm.org/D130532

For power-of-2 C:
((X s>> ShiftC) ^ X) u< C --> (X + C) u< (C << 1)
((X s>> ShiftC) ^ X) u> (C - 1) --> (X + C) u> ((C << 1) - 1)

(https://github.com/llvm/llvm-project/issues/56479)

Test plan:
0/ ninja check-llvm check-clang + bootstrap LLVM/Clang
1/ https://alive2.llvm.org/ce/z/eEUfx3

Differential revision: https://reviews.llvm.org/D130433

Fixes https://github.com/llvm/llvm-project/issues/56504

Reviewed By: ldionne, Mordante, huixie90, #libc

Spies: libcxx-commits, hewillk

Differential Revision: https://reviews.llvm.org/D129794

Add baseline tests. NFC.
(https://github.com/llvm/llvm-project/issues/56479)

Test plan:
ninja check-all

Differential revision: https://reviews.llvm.org/D130605

[NFC] Use more appropriate SmallVectorImpl::append call in std::initializer_list SmallVector constructor

Since we are in constructor there is no need to perform redundant call to SmallVectorImpl::clear() inside assign function.
Although calling cheaper append function instead assign doesn't make any difference on optimized builds
(DSE does the job removing stores), we still save some cycles for debug binaries.

Differential Revision: https://reviews.llvm.org/D130361

According to [RISC-V DWARF Specification](https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-dwarf.adoc) add RISCV DWARF Registers.

Don't worry about the difference between riscv32 and riscv64, they just have different bytes of registers.

Reviewed By: DavidSpickett

Differential Revision: https://reviews.llvm.org/D130686