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Re: [Chicken-janitors] #1624: Flonum unboxing too agressive
From: |
Chicken Trac |
Subject: |
Re: [Chicken-janitors] #1624: Flonum unboxing too agressive |
Date: |
Mon, 24 Jun 2019 09:21:49 -0000 |
#1624: Flonum unboxing too agressive
---------------------------------+-------------------
Reporter: sjamaan | Owner:
Type: defect | Status: new
Priority: critical | Milestone: 5.2
Component: compiler | Version: 5.1.0
Resolution: | Keywords: lfa2
Estimated difficulty: medium |
---------------------------------+-------------------
Description changed by sjamaan:
Old description:
> Found by Sven Hartrumpf. The following program will segfault:
>
> {{{
> (define (test-it)
> (let loop ((done #f))
> (if done
> '()
> (cons (or (read) 0.0) (loop #t)))))
>
> (print (test-it))
> }}}
>
> When run with a {{{DEBUGBUILD}}} CHICKEN, you'll see it fails with a nice
> panic due to a low-level assertion error triggered by a
> {{{C_flonum_magnitude}}} call when you enter a fixnum:
>
> {{{
> [panic] Low-level type assertion
> C_blockp((C_word)C_VAL1(C__PREV_TMPST.n1))=#t failed at test.c:176 -
> execution terminated
> }}}
>
> Generated code failing:
>
> {{{
> /* k150 in loop in test-it in k131 in k128 in k125 */
> static void C_ccall f_152(C_word c,C_word *av){
> C_word tmp;
> C_word t0=av[0];
> C_word t1=av[1];
> C_word t2;
> C_word t3;
> C_word t4;
> double f0;
> C_word *a;
> C_check_for_interrupt;
> if(C_unlikely(!C_demand(C_calculate_demand(8,c,2)))){
> C_save_and_reclaim((void *)f_152,2,av);}
> a=C_alloc(8);
> f0=C_flonum_magnitude((C_truep(t1)?t1:lf[1])); /// <--- offending code
> t2=C_flonum(&a,f0);
> t3=(*a=C_CLOSURE_TYPE|3,a[1]=(C_word)f_159,a[2]=((C_word*)t0)[2],a[3]=t2,tmp=(C_word)a,a+=4,tmp);
> C_trace(C_text("test.scm:5: loop"));
> t4=((C_word*)((C_word*)t0)[3])[1];
> f_141(t4,t3,C_SCHEME_TRUE);}
> }}}
>
> Most likely introduced by 79cf7427638eebf695f2be54731bb6bbf4d0fff2.
New description:
Found by Sven Hartrumpf. The following program will segfault:
{{{
(define (test-it)
(let loop ((done #f))
(if done
'()
(cons (or (read) 0.0) (loop #t)))))
(print (test-it))
}}}
When run with a {{{DEBUGBUILD}}} CHICKEN, you'll see it fails with a nice
panic due to a low-level assertion error triggered by a
{{{C_flonum_magnitude}}} call when you enter a fixnum:
{{{
[panic] Low-level type assertion
C_blockp((C_word)C_VAL1(C__PREV_TMPST.n1))=#t failed at test.c:176 -
execution terminated
}}}
Generated code failing:
{{{
/* k150 in loop in test-it in k131 in k128 in k125 */
static void C_ccall f_152(C_word c,C_word *av){
C_word tmp;
C_word t0=av[0];
C_word t1=av[1];
C_word t2;
C_word t3;
C_word t4;
double f0;
C_word *a;
C_check_for_interrupt;
if(C_unlikely(!C_demand(C_calculate_demand(8,c,2)))){
C_save_and_reclaim((void *)f_152,2,av);}
a=C_alloc(8);
f0=C_flonum_magnitude((C_truep(t1)?t1:lf[1])); /// <--- offending code
t2=C_flonum(&a,f0);
t3=(*a=C_CLOSURE_TYPE|3,a[1]=(C_word)f_159,a[2]=((C_word*)t0)[2],a[3]=t2,tmp=(C_word)a,a+=4,tmp);
C_trace(C_text("test.scm:5: loop"));
t4=((C_word*)((C_word*)t0)[3])[1];
f_141(t4,t3,C_SCHEME_TRUE);}
}}}
Most likely introduced by 79cf7427638eebf695f2be54731bb6bbf4d0fff2.
ALSO: In the generated code in this case, it unboxes and immediately boxes
the flonum. There's no operation in between, so that's wasteful.
It only makes sense with >1 operations (though with exactly 1 it should be
okay too but adds no perf improvement)
--
--
Ticket URL: <https://bugs.call-cc.org/ticket/1624#comment:2>
CHICKEN Scheme <https://www.call-cc.org/>
CHICKEN Scheme is a compiler for the Scheme programming language.