[10] [s390] RFR(XS): micro-optimization in resize_frame_absolute()

[Doerr, Martin]

Hi Lutz,

thanks for providing the webrev.

Is it allowed to write to the stack before updating the SP?
I know that the PPC ABI allows this within a certain range, but I’m not aware of such an exception on s390x.

I’d also prefer separate functions instead of one with so many cases.
E.g. one function which copies the fp and one which takes a given fp like:
void MacroAssembler::resize_frame_absolute(Register newSP, Register fp) {
  assert_different_registers(newSP, fp, Z_SP);
  z_lgr(Z_SP, newSP);
  z_stg(fp, _z_abi(callers_sp), (newSP == Z_R0) ? Z_SP : newSP);
}

Thanks and best regards,
Martin


From: hotspot-compiler-dev [mailto:hotspot-compiler-dev-bounces at openjdk.java.net] On Behalf Of Schmidt, Lutz
Sent: Dienstag, 23. Mai 2017 12:47
To: hotspot-compiler-dev at openjdk.java.net
Subject: [10] [s390] RFR(XS): micro-optimization in resize_frame_absolute()

Dear all,

I would like to request reviews for this tiny, s390-only enhancement:
Bug:    https://bugs.openjdk.java.net/browse/JDK-8180659
Webrev: http://cr.openjdk.java.net/~lucy/webrevs/8180659.00/

Thank you!
Lutz

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