RFR: 8144028: Use AArch64 bit-test instructions in C2

Andrew Haley aph at redhat.com
Wed Nov 25 17:03:25 UTC 2015

On 11/25/2015 04:56 PM, Edward Nevill wrote:
> On Wed, 2015-11-25 at 15:49 +0000, Andrew Haley wrote:
>> For some reason (oversight, I guess) we never got around to using the
>> bit-testing AArch64 instructions in C2.  TBZ/TBNZ are quite nice in
>> that they allow bit tests and branches (and tests for +ve/-ve) without
>> hitting the condition codes.  TST sets the condition codes based on a
>> set of bits in a register: it's an AND which throws the result away.
>> http://cr.openjdk.java.net/~aph/8144028/
> Looks fine. Small typo.
> In cmpL_branch_sign and cmpI_branch_sign
> +  format %{ "cb$cmp   $op1, $labl" %}
> should be "tb$cmp ..."

That's not really a typo.  I thought "tblt" and "tbge" didn't make
much sense.  AFAICS "cblt" looks okay, but I'm not sure:

040 + 	ldrsbw  R12, R1, R13, #16 I2L	# byte
048   	cblt   R12, B30  P=0.000000 C=8345.000000



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