[NFC][DebugInfo] Make some block-start-position methods return iterators (#124287)

As part of the "RemoveDIs" work to eliminate debug intrinsics, we're
replacing methods that use Instruction*'s as

[NFC][DebugInfo] Make some block-start-position methods return iterators (#124287)

As part of the "RemoveDIs" work to eliminate debug intrinsics, we're
replacing methods that use Instruction*'s as positions with iterators. A
number of these (such as getFirstNonPHIOrDbg) are sufficiently
infrequently used that we can just replace the pointer-returning version
with an iterator-returning version, hopefully without much/any
disruption.

Thus this patch has getFirstNonPHIOrDbg and
getFirstNonPHIOrDbgOrLifetime return an iterator, and updates all
call-sites. There are no concerns about the iterators returned being
converted to Instruction*'s and losing the debug-info bit: because the
methods skip debug intrinsics, the iterator head bit is always false
anyway.

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[NFC][DebugInfo] Use iterators for instruction insertion in more places (#124291)

As part of the "RemoveDIs" work to eliminate debug intrinsics, we're
replacing methods that use Instruction*'s as p

[NFC][DebugInfo] Use iterators for instruction insertion in more places (#124291)

As part of the "RemoveDIs" work to eliminate debug intrinsics, we're
replacing methods that use Instruction*'s as positions with iterators.
This patch changes some more complex call-sites, those crossing file
boundaries and where I've had to perform some minor rewrites.

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[NFC][DebugInfo] Use iterator moveBefore at many call-sites (#123583)

As part of the "RemoveDIs" project, BasicBlock::iterator now carries a
debug-info bit that's needed when getFirstNonPHI and sim

[NFC][DebugInfo] Use iterator moveBefore at many call-sites (#123583)

As part of the "RemoveDIs" project, BasicBlock::iterator now carries a
debug-info bit that's needed when getFirstNonPHI and similar feed into
instruction insertion positions. Call-sites where that's necessary were
updated a year ago; but to ensure some type safety however, we'd like to
have all calls to moveBefore use iterators.

This patch adds a (guaranteed dereferenceable) iterator-taking
moveBefore, and changes a bunch of call-sites where it's obviously safe
to change to use it by just calling getIterator() on an instruction
pointer. A follow-up patch will contain less-obviously-safe changes.

We'll eventually deprecate and remove the instruction-pointer
insertBefore, but not before adding concise documentation of what
considerations are needed (very few).

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[CodeGenPrepare] Replace `undef` use with `poison` [NFC] (#123111)

When generating a constant vector, if `UseSplat` is false, the indices
different from the index of the extract can be filled with

[CodeGenPrepare] Replace `undef` use with `poison` [NFC] (#123111)

When generating a constant vector, if `UseSplat` is false, the indices
different from the index of the extract can be filled with `poison`
instead of `undef`.

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[CodeGen] Avoid repeated hash lookups (NFC) (#123016)

[LLVM] Fix various cl::desc typos and whitespace issues (NFC) (#121955)

PatternMatch: migrate to CmpPredicate (#118534)

With the introduction of CmpPredicate in 51a895a (IR: introduce struct
with CmpInst::Predicate and samesign), PatternMatch is one of the first
key p

PatternMatch: migrate to CmpPredicate (#118534)

With the introduction of CmpPredicate in 51a895a (IR: introduce struct
with CmpInst::Predicate and samesign), PatternMatch is one of the first
key pieces of infrastructure that must be updated to match a CmpInst
respecting samesign information. Implement this change to Cmp-matchers.

This is a preparatory step in migrating the codebase over to
CmpPredicate. Since we no functional changes are desired at this stage,
we have chosen not to migrate CmpPredicate::operator==(CmpPredicate)
calls to use CmpPredicate::getMatching(), as that would have visible
impact on tests that are not yet written: instead, we call
CmpPredicate::operator==(Predicate), preserving the old behavior, while
also inserting a few FIXME comments for follow-ups.

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[CodeGenPrepare] Drop nsw flags in `optimizeLoadExt` (#118180)

Alive2: https://alive2.llvm.org/ce/z/pMcD7q
Closes https://github.com/llvm/llvm-project/issues/118172.

[CodeGen] Remove unused includes (NFC) (#115996)

Identified with misc-include-cleaner.

[CGP] [CodeGenPrepare] Folding `urem` with loop invariant value plus offset (#104724)

This extends the existing fold:

```
for(i = Start; i < End; ++i)
Rem = (i nuw+- IncrLoopInvariant) u% Re

[CGP] [CodeGenPrepare] Folding `urem` with loop invariant value plus offset (#104724)

This extends the existing fold:

```
for(i = Start; i < End; ++i)
Rem = (i nuw+- IncrLoopInvariant) u% RemAmtLoopInvariant;
```
->
```
Rem = (Start nuw+- IncrLoopInvariant) % RemAmtLoopInvariant;
for(i = Start; i < End; ++i, ++rem)
Rem = rem == RemAmtLoopInvariant ? 0 : Rem;
```

To work with a non-zero `IncrLoopInvariant`.

This is a common usage in cases such as:

```
for(i = 0; i < N; ++i)
if ((i + 1) % X) == 0)
do_something_occasionally_but_not_first_iter();
```

Alive2 w/ i4/unrolled 6x (needs to be ran locally due to timeout):
https://alive2.llvm.org/ce/z/6tgyN3

Exhaust proof over all uint8_t combinations in C++:
https://godbolt.org/z/WYa561388

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Check hasOptSize() in shouldOptimizeForSize() (#112626)

replace 2 placeholder uses of undef with poison [NFC]

Reland `[CodeGenPrepare] Convert `ctpop(X) ==/!= 1` into `ctpop(X) u</u> 2/1` (#111284)` (#111998)

Relands #111284. Test failure with stage2 build has been fixed by
https://github.com/llvm/llvm-pr

Reland `[CodeGenPrepare] Convert `ctpop(X) ==/!= 1` into `ctpop(X) u</u> 2/1` (#111284)` (#111998)

Relands #111284. Test failure with stage2 build has been fixed by
https://github.com/llvm/llvm-project/pull/111946.


Some targets have better codegen for `ctpop(X) u< 2` than `ctpop(X) ==
1`. After https://github.com/llvm/llvm-project/pull/100899, we set the
range of ctpop's return value to indicate the argument/result is
non-zero.

This patch converts `ctpop(X) ==/!= 1` into `ctpop(X) u</u> 2/1` in CGP
to fix https://github.com/llvm/llvm-project/issues/95255.

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Revert "[CodeGenPrepare] Convert `ctpop(X) ==/!= 1` into `ctpop(X) u</u> 2/1`" (#111932)

Reverts llvm/llvm-project#111284 to fix clang stage2 builds.
Investigating...

Failed buildbots:
https://

Revert "[CodeGenPrepare] Convert `ctpop(X) ==/!= 1` into `ctpop(X) u</u> 2/1`" (#111932)

Reverts llvm/llvm-project#111284 to fix clang stage2 builds.
Investigating...

Failed buildbots:
https://lab.llvm.org/buildbot/#/builders/76/builds/3576
https://lab.llvm.org/buildbot/#/builders/168/builds/4308
https://lab.llvm.org/buildbot/#/builders/127/builds/1087

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[CodeGenPrepare] Convert `ctpop(X) ==/!= 1` into `ctpop(X) u</u> 2/1` (#111284)

Some targets have better codegen for `ctpop(X) u< 2` than `ctpop(X) ==
1`. After https://github.com/llvm/llvm-project

[CodeGenPrepare] Convert `ctpop(X) ==/!= 1` into `ctpop(X) u</u> 2/1` (#111284)

Some targets have better codegen for `ctpop(X) u< 2` than `ctpop(X) ==
1`. After https://github.com/llvm/llvm-project/pull/100899, we set the
range of ctpop's return value to indicate the argument/result is
non-zero.

This patch converts `ctpop(X) ==/!= 1` into `ctpop(X) u</u> 2/1` in CGP
to fix https://github.com/llvm/llvm-project/issues/95255.

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[TTI] NFC: Port TLI.shouldSinkOperands to TTI (#110564)

Porting to TTI provides direct access to the instruction cost model,
which can enable instruction cost based sinking without introducing code

[TTI] NFC: Port TLI.shouldSinkOperands to TTI (#110564)

Porting to TTI provides direct access to the instruction cost model,
which can enable instruction cost based sinking without introducing code
duplication.

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[CGP] Undo constant propagation of pointers across calls

It may be profitable to revert SCCP propagation of C++ static values,
if such constants are pointers, in order to avoid redundant pointer
com

[CGP] Undo constant propagation of pointers across calls

It may be profitable to revert SCCP propagation of C++ static values,
if such constants are pointers, in order to avoid redundant pointer
computation, since the method returning the constant is non-removable.

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[ExtendLifetimes] Implement llvm.fake.use to extend variable lifetimes (#86149)

This patch is part of a set of patches that add an `-fextend-lifetimes`
flag to clang, which extends the lifetimes of

[ExtendLifetimes] Implement llvm.fake.use to extend variable lifetimes (#86149)

This patch is part of a set of patches that add an `-fextend-lifetimes`
flag to clang, which extends the lifetimes of local variables and
parameters for improved debuggability. In addition to that flag, the
patch series adds a pragma to selectively disable `-fextend-lifetimes`,
and an `-fextend-this-ptr` flag which functions as `-fextend-lifetimes`
for this pointers only. All changes and tests in these patches were
written by Wolfgang Pieb (@wolfy1961), while Stephen Tozer (@SLTozer)
has handled review and merging. The extend lifetimes flag is intended to
eventually be set on by `-Og`, as discussed in the RFC
here:

https://discourse.llvm.org/t/rfc-redefine-og-o1-and-add-a-new-level-of-og/72850

This patch implements a new intrinsic instruction in LLVM,
`llvm.fake.use` in IR and `FAKE_USE` in MIR, that takes a single operand
and has no effect other than "using" its operand, to ensure that its
operand remains live until after the fake use. This patch does not emit
fake uses anywhere; the next patch in this sequence causes them to be
emitted from the clang frontend, such that for each variable (or this) a
fake.use operand is inserted at the end of that variable's scope, using
that variable's value. This patch covers everything post-frontend, which
is largely just the basic plumbing for a new intrinsic/instruction,
along with a few steps to preserve the fake uses through optimizations
(such as moving them ahead of a tail call or translating them through
SROA).

Co-authored-by: Stephen Tozer <stephen.tozer@sony.com>

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[MachineLoopInfo] Fix getLoopID to handle multi latches. (#106195)

This patch also fixed `CodegenPrepare` to preserve loop metadata when
merging blocks.

This fixes issue #102632

Recommit "[CodeGenPrepare] Folding `urem` with loop invariant value"

Was missing remainder on `Start` value.

Also changed logic as as nikic suggested (getting loop from `PN`
instead of `Rem`). The

Recommit "[CodeGenPrepare] Folding `urem` with loop invariant value"

Was missing remainder on `Start` value.

Also changed logic as as nikic suggested (getting loop from `PN`
instead of `Rem`). The prior impl increased the complexity of the code
and made debugging it more difficult.

Closes #104877

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Revert "[CodeGenPrepare] Folding `urem` with loop invariant value"

This reverts commit c64ce8bf283120fd145a57d0e61f9697f719139d.

Seems to be causing stage2 failures on buildbots. Reverting while I

Revert "[CodeGenPrepare] Folding `urem` with loop invariant value"

This reverts commit c64ce8bf283120fd145a57d0e61f9697f719139d.

Seems to be causing stage2 failures on buildbots. Reverting while I
investigate.

show more ...

[CodeGenPrepare] Folding `urem` with loop invariant value

```
for(i = Start; i < End; ++i)
Rem = (i nuw+ IncrLoopInvariant) u% RemAmtLoopInvariant;
```
->
```
Rem = (Start nuw+ IncrLoopInvariant

[CodeGenPrepare] Folding `urem` with loop invariant value

```
for(i = Start; i < End; ++i)
Rem = (i nuw+ IncrLoopInvariant) u% RemAmtLoopInvariant;
```
->
```
Rem = (Start nuw+ IncrLoopInvariant) % RemAmtLoopInvariant;
for(i = Start; i < End; ++i, ++rem)
Rem = rem == RemAmtLoopInvariant ? 0 : Rem;
```

In its current state, only if `IncrLoopInvariant` and `Start` both
being zero.

Alive2 seemed unable to prove this (see:
https://alive2.llvm.org/ce/z/ATGDp3 which is clearly wrong but still
checks out...) so wrote an exhaustive test here:
https://godbolt.org/z/WYa561388

Closes #96625

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[NFC] Cleanup in ADT and Analysis headers. (#104484)

Remove unused directly includes and forward declarations in ADT and
Analysis headers.

[CodeGen] Use a range-based for loop (NFC) (#104408)

[CGP] Use getAllOnesValue()

Split out from https://github.com/llvm/llvm-project/pull/80309.