bug#5754: Bytecomp Arithmetic test failed

[Juri Linkov]

> I tried to run some tests in the `test' subdir,
> and `bytecomp-testsuite-run' in `test/bytecomp-testsuite.el' fails
> on one test: (let ((a (expt 2 -1074)) (b 0.125)) (* a 8 b))
> returns 5e-324 when evaluated by interpreter,
> but after byte-compilation returns 0.0

This bug is caused by optimization in byte-compilation
that changes the order of function arguments.

It byte-compiles

  (let ((a (expt 2 -1074)) (b 0.125)) (* a 8 b))

to

0       constant  expt
1       constant  2
2       constant  -1074
3       call      2
4       constant  0.125
5       varbind   b
6       varbind   a
7       constant  *
8       varref    a
9       varref    b
10      constant  8
11      call      3
12      unbind    2
13      return

where the order of arguments 8-10 is changed from (* a 8 b) to (* a b 8)

For this test the different order of arguments changes
the returned value:

(funcall '* 5e-324 8 0.125)
=> 5e-324

(funcall '* 5e-324 0.125 8)
=> 0.0

-- 
Juri Linkov
http://www.jurta.org/emacs/