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AOT: implement non-speculative int64 versions of MOD and TRUNCDIV #33967

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mraleph opened this Issue Jul 24, 2018 · 6 comments

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mraleph commented Jul 24, 2018

Our compiler does not inline / specialize int.% or int.~/ even on platforms where there are short enough instruction sequences.

On ARM64 we should probably always emit sdiv for TRUNCDIV and sdiv+msub for MOD.

On ARM32 we probably emit whatever we emit for IntegerDivision or maybe a call to __aeabi_ldivmod - if that is better.

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aartbik commented Jul 27, 2018

This is a blocking AOT optimization of any integer operation chain with % or ~/. We should start supporting this at the very least on 64-bit architectures.

@aartbik aartbik self-assigned this Jul 27, 2018

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aartbik commented Jul 27, 2018

While working on this I noticed the current VM is not completely accurate for

0x8000000000000000 % -1 
0x8000000000000000 ~/ -1 

(logical outcomes are 0 and 0x8000000000000000) but our 64-bit arch crash with a floating-point exceptions).

@aartbik aartbik closed this Jul 27, 2018

@aartbik aartbik added this to Done in Modern Dart VM Pipeline via automation Jul 27, 2018

@aartbik aartbik reopened this Jul 27, 2018

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aartbik commented Jul 27, 2018

Still getting used to the buttons :-) I obviously hit the "close and comment" rather than just the "comment".

dart-bot pushed a commit that referenced this issue Jul 28, 2018

[vm/compiler] Bug fix in 64-bit MOD (%) operator.
Rationale:
While writing tests for the ongoing native 64-bit
MOD/TRUNCDIV support in AOT, I noticed a floating-point
crash in our VM due to evaluating the constant mod case:

  Expect.equals(0, mod(minInt64, -1));
  Expect.equals(minInt64, truncdiv(minInt64, -1));

This fixes the constant evaluation part.

#33967

Change-Id: I9a4e6b3cd4d0d0dee39c690d2b981b5812501be4
Reviewed-on: https://dart-review.googlesource.com/67281
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Aart Bik <ajcbik@google.com>

dart-bot pushed a commit that referenced this issue Jul 31, 2018

[vm/compiler] Bug fix in 64-bit MOD (%) operator.
Rationale:
While writing tests for the ongoing native 64-bit
MOD/TRUNCDIV support in AOT, I noticed a floating-point
crash in our VM due to evaluating the constant mod case:

  Expect.equals(0, mod(minInt64, -1));
  Expect.equals(minInt64, truncdiv(minInt64, -1));

This fixes the constant evaluation part.

#33967

Change-Id: I9a4e6b3cd4d0d0dee39c690d2b981b5812501be4
Reviewed-on: https://dart-review.googlesource.com/67281
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Aart Bik <ajcbik@google.com>

dart-bot pushed a commit that referenced this issue Aug 1, 2018

[vm/compiler] Non-speculative X64 long division/remainder.
Rationale:
Having a non-speculative implementation avoids deopting
under JIT and enables AOT.

#33967

Change-Id: Ib38200502f5a8f63912ff5d7a808ea6e27f9001d
Reviewed-on: https://dart-review.googlesource.com/67502
Commit-Queue: Aart Bik <ajcbik@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>

dart-bot pushed a commit that referenced this issue Aug 2, 2018

[vm/compiler] Non-speculative ARM64 long division/remainder.
Rationale:
Having a non-speculative implementation avoids deopting
under JIT and enables AOT. Done for X64 and now also ARM64.

#33967

Change-Id: I83302a5950aa2dc1a7220367755af748cfaa4393
Reviewed-on: https://dart-review.googlesource.com/67920
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Aart Bik <ajcbik@google.com>

dart-bot pushed a commit that referenced this issue Aug 3, 2018

[vm/compiler] Various 64-bit operator improvements.
Rationale:
Improves the slow path of 64-bit REM/TRUNCDIV on
X64 and ARM64. Also introduces 64-bit negate operator,
which was needed to expose negative contants
(viz. x / -3 was represented as x / - (3) first).
The negate operator is not recognized in AOT mode yet,
since shifts by out-of-range constants should learn
how to throw rather than deopt....


#33967
flutter/flutter#19677

Change-Id: I7d81c9b1c72d99e8c4018f68c0501c7b599e073f
Reviewed-on: https://dart-review.googlesource.com/68280
Commit-Queue: Aart Bik <ajcbik@google.com>
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>

dart-bot pushed a commit that referenced this issue Aug 10, 2018

[vm/compiler] "fast"-path for x64 division
Rationale:
Since 64-bit division requires twice as many cycles
and has much higher latency compared to the 32-bit
division, even for a non-speculative 64-bit path,
a 32-bit "fast path" makes sense.

Speedup:
About 2x for cases that fit 32-bits. No noticable
slowdown for the 64-bit cases.

flutter/flutter#19677
#33967

Change-Id: I0d3b44564fee2cda03fc36f089a4424084732de0
Reviewed-on: https://dart-review.googlesource.com/69200
Commit-Queue: Aart Bik <ajcbik@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
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mkustermann commented Sep 13, 2018

@aartbik If you've already handled this issue, consider closing it.

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aartbik commented Sep 13, 2018

I kept this open for an ARM32 implementation (probably a lib call).

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aartbik commented Feb 12, 2019

Closing this issue after all. The 64-bit cases are now fully optimized, as requested. Handling the arm32 case with a lib call (compared to a call into the runtime) does not seem worth the engineering effort.

@aartbik aartbik closed this Feb 12, 2019

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