RFR: 8272563: Possible assertion failure in CardTableBarrierSetC1

[Igor Veresov]

On Wed, 18 Aug 2021 12:37:00 GMT, Fairoz Matte <fmatte at openjdk.org> wrote:

> This patch is proposed by the submitter of the bug - ugawa at ci.i.u-tokyo.ac.jp
> 
> The method CardTableBarrierSetC1::post_barrier generates a move LIR when TwoOperandLIRForm flag is true to move the address to be marked in the card table to a temporary register.
>> __ move(addr, tmp);
> However, this code only guarantees that `addr` is a valid register for LIR, which can be a virtual register. If the virtual register for `addr` is spilled to the stack by chance, the `move(addr, tmp)` is compiled to a memory-to-register which causes an assertion failure because a memory-to-register move requires their arguments to have the same size. 
> The fix is to check if it is is_oop() and call the mov appropriately.
> 
> No issues found in local testing and Mach5 tier1-3

Well, an extra temp register won't solve it, right? You're just getting lucky that tmp2 is not getting spilled. If that happens you get exactly the same situation as before, don't you?

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PR: https://git.openjdk.java.net/jdk/pull/5164