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Subject: |
floating point unboxing regression in 2.2.3 |
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Date: |
Sun, 7 Jan 2018 22:16:17 -0500 |
Hello,
Guile 2.2.3 seems to have lost some of the abilities that Guile 2.2.2
had wrt unboxing floats. Here's a simple procedure to show the
problem. It simply adds the first two elements of an f32vector:
(define (add-two-floats bv)
(+ (f32vector-ref bv 0) (f32vector-ref bv 1)))
Here's the disassembly from 2.2.2 (note that f64->scm appears only once):
Disassembly of #<procedure add-two-floats (bv)> at #x7efef4006230:
0 (assert-nargs-ee/locals 2 1) ;; 3 slots (1 arg) at
(unknown file):22:0
1 (load-u64 2 0 0) at
(unknown file):23:26
4 (bv-f32-ref 2 1 2)
5 (load-u64 0 0 4) at
(unknown file):23:47
8 (bv-f32-ref 1 1 0)
9 (fadd 2 2 1) at
(unknown file):23:23
10 (f64->scm 1 2)
11 (handle-interrupts)
12 (return-values 2) ;; 1 value
And here is 2.2.3:
Disassembly of #<procedure add-two-floats (bv)> at #x2457140:
0 (assert-nargs-ee/locals 2 1) ;; 3 slots (1 arg) at
(unknown file):29:0
1 (load-u64 2 0 0) at
(unknown file):30:26
4 (bv-f32-ref 2 1 2)
5 (f64->scm 2 2)
6 (load-u64 0 0 4) at
(unknown file):30:47
9 (bv-f32-ref 1 1 0)
10 (f64->scm 1 1)
11 (scm->f64 2 2) at
(unknown file):30:23
12 (scm->f64 1 1)
13 (fadd 2 2 1)
14 (f64->scm 1 2)
15 (handle-interrupts)
16 (return-values 2) ;; 1 value
2.2.3 is reading unboxed floats from the bytevector, boxing them,
unboxing them, then calling fadd. The result is that some formerly
well optimized code of mine that generated little to no garbage is now
generating lots of garbage. Is this intentional due to the
"instruction explosion" work going on is it a legitimate bug?
Thanks,
- Dave
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--- Begin Message ---
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Subject: |
Re: bug#30020: floating point unboxing regression in 2.2.3 |
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Date: |
Mon, 11 Jun 2018 10:26:50 -0400 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) |
Mark H Weaver <address@hidden> writes:
> I did the moral equivalent of a git bisect, and found the culprit:
>
> commit d4883307ca64a7028b9a6cd072974437306c19d3
> Author: Andy Wingo <address@hidden>
> Date: Thu Nov 30 10:41:45 2017 +0100
>
> Minor CSE run-time optimization
>
> * module/language/cps/cse.scm (compute-equivalent-subexpressions): Minor
> optimization to reduce the size of equivalent expression keys, and to
> avoid some work if an expression has no key.
>
> Fortunately, this commit can be reverted in isolation without any
> difficulty, and apparently without any negative consequences. If a
> better solution isn't found soon, perhaps that's what we should do.
I pushed commit df93752479ab88446f5db4b1d6ebf53a85c7593f to the
stable-2.2 branch, which reverts the above commit. I'm closing this
bug, but feel free to reopen if there are still issues to resolve.
Thanks,
Mark
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