RFR: JDK-8297660: x86: Redundant test+jump in C1 allocateArray

Sat Nov 26 10:49:06 UTC 2022

On Sat, 26 Nov 2022 09:48:07 GMT, Andrew Haley <aph at openjdk.org> wrote:

> Surely a macro assembler function that takes a length should not misbehave of that length is zero. It's a fairly basic correctness criterion that it most not, because zero is a valid number. We shouldn't be building fragility into the system. I agree that it makes sense to remove one of the checks, but it should be the one in the caller.

Okay, did that.

I did it the other way around originally since the outer test cannot be removed, it's the sub of the header size. So the test in zero_memory is still redundant, but the outer jz has been removed at least:

  0x00007f8080ca2f02:   sub    $0x10,%rsi  << initialize_body
  0x00007f8080ca2f06:   test   %rsi,%rsi      << zero_memory
  0x00007f8080ca2f09:   je     0x00007f8080ca2f20 << zero_memory

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PR: https://git.openjdk.org/jdk/pull/11372