Checking affines for instructions

[harish c]

Hello All,

I find trouble understanding the below scalar expressions. Can someone help me understand why the below expressions are not affine.

Expr: {{((8 * %8) + (-1 * %2) + %13),+,1}<%pregion_for_entry.entry.i>,+,(1 + (-1 * %2)),+,1}<%while.body.i>
Region: pregion_for_entry.entry.i => transpose_ceWork.exit
 -> INVALID: AddRec is not affine
Non affine loop bound '***COULDNOTCOMPUTE***' in loop: while.body.i

Expr: %18
Region: while.end.i => if.end.r_exit.i
 ->   %18 = phi i32 [ %add1.i.i, %pregion_for_entry.entry.i ], [ %sub.i.lcssa, %while.end.i.loopexit ] ; instructoin in IR
INVALID: UnknownExpr references an instruction within the region

Thanks in advance.

Regards,

Harish C

[Harish]

Thank you for the clarification. 

On Thu, 13 May, 2021, 8:24 am Michael Kruse, <Michae...@meinersbur.de> wrote:

This is from the -debug-only=polly-scev-validator output which is only
really useful when debugging. It tries to diagnose why an expression
is not affine.

In the first case the expression is not an affine recurrence equation,
but a quadratic one. (reduced: {X,+,Y,+,1}<%while.body.i>)

In the second case an instruction cannot be resolved by
ScalarEvolution, but is also not loop-invariant.

Michael

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