opt: push limit into offset

[ridwanmsharif]

This change pushes the limit into an offset whenever possible.
This shouldn't worsen any plan but does allow the GetLimitedScans
rule to fire in more scenarios.

Fixes #30416.
This is currently blocked on #38659.

Release note: None

[cockroach-teamcity]

This change is 

[RaduBerinde]

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @RaduBerinde and @ridwanmsharif)

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pkg/sql/opt/norm/custom_funcs.go, line 1695 at r1 (raw file):

	firstVal := int64(*first.(*tree.DInt))
	secondVal := int64(*second.(*tree.DInt))
	return tree.NewDInt(tree.DInt(firstVal + secondVal))

We should check for overflow here (or somewhere in the rule).

[ridwanmsharif]

Reviewable status: complete! 0 of 0 LGTMs obtained

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pkg/sql/opt/norm/custom_funcs.go, line 1695 at r1 (raw file):

Previously, RaduBerinde wrote…

We should check for overflow here (or somewhere in the rule).

Done.

[RaduBerinde]

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @RaduBerinde and @ridwanmsharif)

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pkg/sql/opt/norm/custom_funcs.go, line 1694 at r3 (raw file):

// AddConsts adds the numeric constants together. AddConsts assumes the sum
// will not overflow. Call DoesSumOverflow on the constants to guarantee this.
func (c *CustomFuncs) AddConsts(first tree.Datum, second tree.Datum) tree.Datum {

[nit] rename to AddConstInts

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pkg/sql/opt/norm/custom_funcs.go, line 1697 at r3 (raw file):

	firstVal := int64(*first.(*tree.DInt))
	secondVal := int64(*second.(*tree.DInt))
	sum, _ := arith.AddWithOverflow(firstVal, secondVal)

check ok and panic(errors.AssertionFailedf(..)) if it's false

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pkg/sql/opt/norm/custom_funcs.go, line 1702 at r3 (raw file):

// DoesSumOverflow returns true if the addition of the two integers overflows.
func (c *CustomFuncs) DoesSumOverflow(first tree.Datum, second tree.Datum) bool {

[nit] I'd invert the result and rename to CanAddConstInts

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pkg/sql/opt/norm/rules/limit.opt, line 70 at r3 (raw file):

    (Const $limit:* & (IsPositiveLimit $limit))
    $limitOrdering:* & (IsSameOrdering $offsetOrdering $limitOrdering) &
    ^(DoesSumOverflow $limit $offset)

[nit] indent this line (4 spaces)

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pkg/sql/opt/norm/testdata/rules/limit, line 479 at r3 (raw file):

# Using MaxInt64. Do not apply rule when sum overflows.
opt expect-not=(PushLimitIntoOffset)

[nit] parens not necessary

[ridwanmsharif]

TFTR!

bors r+

Reviewable status: complete! 0 of 0 LGTMs obtained (and 1 stale)

[craig]

Build succeeded

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