Integrated: 8288467: remove memory_operand assert for spilled instructions

[Emanuel Peter]

On Fri, 17 Jun 2022 09:32:40 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> In [JDK-8282555](https://bugs.openjdk.org/browse/JDK-8282555) I added this assert, because on x64 this seems to always hold. But it turns out there are instructions on x86 (32bit) that violate this assumption.
> 
> **Why it holds on x64**
> It seems we only ever do one read or one write per instruction. Instructions with multiple memory operands are extremely rare.
> 1. we spill from register to memory: we land in the if case, where the cisc node has an additional input slot for the memory edge.
> 2. we spill from register to stackSlot: no additional input slot is reserved, we land in else case and add an additional precedence edge.
> 
> **Why it is violated on x86 (32bit)**
> We have additional cases that land in the else case. For example spilling `src1` from `addFPR24_reg_mem` to `addFPR24_mem_cisc`.
> https://urldefense.com/v3/__https://github.com/openjdk/jdk19/blob/53bf1bfdabb79b37afedd09051d057f9eea620f2/src/hotspot/cpu/x86/x86_32.ad*L10325-L10327__;Iw!!ACWV5N9M2RV99hQ!Pr4vQtunH8vkcMdyxfszAANmzlFV4z9EWDUZa2J6jaD5UAxLshARsO-Ez7wih6YWUn_DxO5ApSlxRc4Wlbiv4aOkwpX9LA$  https://urldefense.com/v3/__https://github.com/openjdk/jdk19/blob/53bf1bfdabb79b37afedd09051d057f9eea620f2/src/hotspot/cpu/x86/x86_32.ad*L10368-L10370__;Iw!!ACWV5N9M2RV99hQ!Pr4vQtunH8vkcMdyxfszAANmzlFV4z9EWDUZa2J6jaD5UAxLshARsO-Ez7wih6YWUn_DxO5ApSlxRc4Wlbiv4aPA5Wmz3w$ 
> We land in the else case, because both have 2 inputs, thus `oper_input_base() == 2`.
> And both have memory operands, so the assert must fail.
> 
> **Solutions**
> 1. Remove the Assert, as it is incorrect.
> 2. Extend the assert to be correct.
>    - case 1: reg to mem spill, where we have a reserved input slot in cisc for memory edge
>    - case 2: reg to stackSlot spill, where both mach and cisc have no memory operand.
>    - other cases, with various register, stackSlot and memory inputs and outputs. We would have to find a general rule, and test it properly, which is not trivial because getting registers to spill is not easy to precisely provoke.
> 3. Have platform dependent asserts. But also this makes testing harder.
> 
> For now I went with 1. as it is simple and as far as I can see correct.
> 
> Running tests on x64 (should not fail). **I need someone to help me with testing x86 (32bit)**. I only verified the reported test failure with a 32bit build.

This pull request has now been integrated.

Changeset: af051391
Author:    Emanuel Peter <epeter at openjdk.org>
URL:       https://git.openjdk.org/jdk19/commit/af05139133530871c88991aa0340205cfc44972a
Stats:     7 lines in 1 file changed: 5 ins; 0 del; 2 mod

8288467: remove memory_operand assert for spilled instructions

Reviewed-by: thartmann, shade, jbhateja

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PR: https://git.openjdk.org/jdk19/pull/33