From: Jonas Amoson <jonas.amoson@gmail.com>
To: 9front@9front.org
Subject: [9front] Weird >>= operator behaviour in 5c/5l
Date: Sun, 17 Jan 2021 23:36:08 +0200 [thread overview]
Message-ID: <CAF46DJ74p1mmkjbN4wavNW+VeLGQiA-XJ2Ohg0hT=LO2FZdmOg@mail.gmail.com> (raw)
Dear list,
It looks to me that the operation x >>= 0 doesn't generate the
correct result with 5c/5l (32-bit arm on Rpi 1b+). Example:
x = 2;
x >>= 0;
Gives x == 0 on arm, but on 386 it yields x == 2 as expected.
The non shorted form: x = x >> 0; Gives the correct result.
Is this a known issue, or I am missing something?
Looking at the assembly, the operation seems to be eliminated
if using the long form (giving the correct result) but using the
shorted form generates an instruction SRL $0, R1, R2, which
doesn't seem to work. Other shifts (e.g. x>>=1) do work (e.g.
generating SRL $1, R1, R2).
//Jonas Amoson
#include <u.h>
#include <libc.h>
void
main()
{
unsigned int x = 2;
print("%ud\n", x >>= 0);
exits(nil);
}
next reply other threads:[~2021-01-17 22:05 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-17 21:36 Jonas Amoson [this message]
2021-01-18 4:05 ` Noam Preil
2021-01-18 5:20 ` ori
2021-01-18 16:11 ` Jonas Amoson
2021-01-20 5:59 ` ori
2021-01-20 6:12 ` ori
2021-01-20 12:06 ` Jonas Amoson
2021-01-20 22:11 ` Anthony Martin
2021-01-20 23:39 ` ori
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