Re: Address rejected by TARGET_LEGITIMATE_ADDRESS_P recreated in post reload CSE pass at -O2

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Ayonam Ray <ayonam@xxxxxxxxx> writes:

> I have an address (symbolicRef + indexReg * scaleFactor) that is
> rejected by my TARGET_LEGITIMATE_ADDRESS_P.  However, at -O2, the same
> address gets recreated in the post reload CSE pass.  The symbolic
> reference just after the reload is in a register and the address
> "register + indexReg * scaleFactor" is a valid address for my
> architecture.  The CSE figures out that the symbolic reference is in a
> register (the notes say so) and replaces the "register + indexReg *
> scaleFactor" address with "symbolicRef + indexReg * scaleFactor".
>
> Is there a way to prevent this from happening?  Am I missing some
> target definitions which is causing this?  Or is it an incorrect
> predicate definition?
>
> I get the failure in "movsi" when, after the post reload CSE, it tries
> to match the constraints for that memory operand.  The 'm' constraint
> ends up calling the TARGET_LEGITIMATE_ADDRESS_P which returns a zero
> and the constraint check fails.

I'm really guessing here, but it sounds like you have an insn with an
operand that uses an m constraint but for which the operand predicate
accepts operands that do not meet that constraint.  In general for every
RTL that the operand predicate accepts you must have a constraint that
can match that operand.  Based on your description even general_operand
ought to reject the symbolicRef address.

Ian


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