[aarch64-port-dev ] RFR(S): 8241091: AArch64: "bad AD file" with VM option "-XX:-UsePopCountInstruction"

[Andrew Haley]

On 3/19/20 8:08 AM, Pengfei Li wrote:

> Cause is that the PopCountINode or PopCountLNode is created but no
> match rule for it without "UsePopCountInstruction" enabled. One fix
> [1] for this is to avoid creating the nodes. As the CNT instruction
> is available on all AArch64 CPUs and the bitCount() would be ~7x
> slower (according to my local test) if it's disabled, there is
> another fix [2] that force the flag to be true on AArch64. But I'm
> not sure if it's good to ignore a general vm option in an
> architecture backend.

We could go either way, but there's no point in disabling popcount on
AArch64. So [2], but please produce an error message if
"-UsePopCountInstruction" is used.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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