[NFC] Split lambda into 2 parts for further reuse

[IndVars] Use knowledge about execution on last iteration when removing checks

If we know that some check will not be executed on the last iteration, we can use this
fact to eliminate its check.

Di

[IndVars] Use knowledge about execution on last iteration when removing checks

If we know that some check will not be executed on the last iteration, we can use this
fact to eliminate its check.

Differential Revision: https://reviews.llvm.org/D88210
Reviwed By: ebrevnov

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[NFC] Simplify code in IndVars

Return "[IndVars] Remove monotonic checks with unknown exit count"

This reverts commit e038b60d9169733367393f733058f0ff23c28d3f.
This reverts commit a0d84d80315d0c725b5efcd889928bad1171ba56.

This r

Return "[IndVars] Remove monotonic checks with unknown exit count"

This reverts commit e038b60d9169733367393f733058f0ff23c28d3f.
This reverts commit a0d84d80315d0c725b5efcd889928bad1171ba56.

This revert was a mistake. The reason of the failures was
"Use uint64_t for branch weights instead of uint32_t"

Differential Revision: https://reviews.llvm.org/D87832

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Revert "[IndVars] Remove monotonic checks with unknown exit count"

This reverts commit c6ca26c0bfedb8f80d6f8cb9adde25b1d6aac1c5.
This breaks stage2 builds due to hitting this assert:
```
Assertio

Revert "[IndVars] Remove monotonic checks with unknown exit count"

This reverts commit c6ca26c0bfedb8f80d6f8cb9adde25b1d6aac1c5.
This breaks stage2 builds due to hitting this assert:
```
Assertion failed: (WeightSum <= UINT32_MAX && "Expected weights to scale down to 32 bits"), function calcMetadataWeights
```
when compiling AArch64RegisterBankInfo.cpp in LLVM.

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Revert "[NFC] Factor away lambda's redundant parameter"

This reverts commit fdc845b36130d162e5a66e427bf69b2c37b6c6bb.
It seems to be a follow-up to c6372b3fb495 which will be reverted.

[NFC] Factor away lambda's redundant parameter

[IndVars] Remove monotonic checks with unknown exit count

Even if the exact exit count is unknown, we can still prove that this
exit will not be taken. If we can prove that the predicate is monotoni

[IndVars] Remove monotonic checks with unknown exit count

Even if the exact exit count is unknown, we can still prove that this
exit will not be taken. If we can prove that the predicate is monotonic,
fulfilled on first & last iteration, and no overflow happened in between,
then the check can be removed.

Differential Revision: https://reviews.llvm.org/D87832
Reviewed By: apilipenko

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Fix broken build after previous commit

[NFC] Remove unused funciton param

[NFC] Factor out common code into lambda for further improvement

[IndVars] Use contextual knowledge when proving trivial conds

No exact example where it would help, but it's a generally a more
powerful way to prove predicates.

[SCEV][NFC] Cache symbolic max exit count

We want to have a caching version of symbolic BE exit count
rather than recompute it every time we need it.

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

[SCEV][NFC] Cache symbolic max exit count

We want to have a caching version of symbolic BE exit count
rather than recompute it every time we need it.

Differential Revision: https://reviews.llvm.org/D89954
Reviewed By: nikic, efriedma

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[Indvars][NFCI] Simplify assertion.

This should be semantically identical. Also avoids unused variable
warnings in Release builds.

[Indvars][NFC] Merge two functions together

Logic of widenWithVariantUse is split into check and transform
part, unlike any other transform in IndVars. We want to pass some
extra flags from analysis

[Indvars][NFC] Merge two functions together

Logic of widenWithVariantUse is split into check and transform
part, unlike any other transform in IndVars. We want to pass some
extra flags from analysis to transform part and standartize
the code at once, so merging them together.

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[Indvars][NFCI] Remove meaningless restrictive code in IndVars

Variable ExtendOperExpr only exists to check whether it is a SCEV ext.
We create it as SCEV ext right here, so semantically this check

[Indvars][NFCI] Remove meaningless restrictive code in IndVars

Variable ExtendOperExpr only exists to check whether it is a SCEV ext.
We create it as SCEV ext right here, so semantically this check is
trivially true. In theory, it may fail if SCEV is smart enough and can
simplify the expression. However, no matter whether it is an ext or not,
we never use this fact for further reasoning. So this code is currently
useless and in theory may become harmful with SCEV's development.

We do not expect any behavior changes with removing it. If it caused
negative changes, the patch should be reverted.

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[Indvars][NFC] Remove duplicating checks

Some facts have already been checked in widenWithVariantUse and then
checked again in widenWithVariantUseCodegen. The latter is redundant,
we can replace it

[Indvars][NFC] Remove duplicating checks

Some facts have already been checked in widenWithVariantUse and then
checked again in widenWithVariantUseCodegen. The latter is redundant,
we can replace it with asserts.

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[NFC] Add option to disable IV widening if needed

IV widening is sometimes a strictly harmful transform (some examples
of this are shown in tests 11, 12 in widen-loop-comp.ll). One of the
reasons of

[NFC] Add option to disable IV widening if needed

IV widening is sometimes a strictly harmful transform (some examples
of this are shown in tests 11, 12 in widen-loop-comp.ll). One of the
reasons of this is that sometimes SCEV fails to prove some facts after
part of guards has been widened.

Though each single such case looks like a bug that can be addressed,
it seems that disabling of IV widening may be profitable in some cases.
We want to have an option to do so. By default, existing behavior is
preserved and IV widening is on.

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[NFC] Use getZero instead of getConstant(0)

[NFC] Use assert instead of checking the guaranteed condition

From preconditions it is known that either A dominates B or
B dominates A. If A does not dominate B, we do not really need
to check it.

[NFC] Use assert instead of checking the guaranteed condition

From preconditions it is known that either A dominates B or
B dominates A. If A does not dominate B, we do not really need
to check it. Assert should be enough. Should save some compile
time.

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[IndVars] Remove exiting conditions that are trivially true/false

When removing exiting loop conditions, we only consider checks for
which we know the exact exit count. We could also eliminate check

[IndVars] Remove exiting conditions that are trivially true/false

When removing exiting loop conditions, we only consider checks for
which we know the exact exit count. We could also eliminate checks for
which the condition is always true/false.

Differential Revision: https://reviews.llvm.org/D87344
Reviewed By: lebedev.ri, reames

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[ValueTracking] Add UndefOrPoison/Poison-only version of relevant functions

This patch adds isGuaranteedNotToBePoison and programUndefinedIfUndefOrPoison.

isGuaranteedNotToBePoison will be used at

[ValueTracking] Add UndefOrPoison/Poison-only version of relevant functions

This patch adds isGuaranteedNotToBePoison and programUndefinedIfUndefOrPoison.

isGuaranteedNotToBePoison will be used at D75808. The latter function is used at isGuaranteedNotToBePoison.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D84242

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[NFC] Move functon from IndVarSimplify to SCEV

This function can be reused in other places.

Differential Revision: https://reviews.llvm.org/D87274
Reviewed By: fhahn, lebedev.ri

[SCEV][IndVarSimplify] insert point should not be block front.

Recommit after removing the unused cast instructions.

Differential Revision: https://reviews.llvm.org/D80975

[IndVarSimplify] Uniformly use emplace_back for DeadInsts, nfc