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From: "deller at gmx dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/102162] Byte-wise access optimized away at -O1 and above
Date: Wed, 01 Sep 2021 21:25:56 +0000 [thread overview]
Message-ID: <bug-102162-4-EtVVBJm2BT@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-102162-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102162
--- Comment #8 from deller at gmx dot de ---
On 9/1/21 11:19 PM, dave.anglin at bell dot net wrote:
>> I think the problem with your testcase is, that the compiler doesn't know the
>> alignment of the parameter "p" in your f_unaligned() function.
>> So it will generate byte-accesses.
> I think it's the type rather than the alignment. If type is char, one gets
> byte accesses. If type is short, one gets 16-bit accesses.
>
> The alignment is being ignored.
You are right.
It's even worse!
short evil;
int f_unaligned2(void)
{ return get_unaligned(&evil); }
gives:
00000000 <f_unaligned2>:
0: 2b 60 00 00 addil L%0,dp,r1
4: 44 3c 00 00 ldh 0(r1),ret0
8: e8 40 c0 00 bv r0(rp)
c: d3 9c 1f f0 extrw,s ret0,31,16,ret0
The "ldh" loads only the first two bytes, and extends it into the upper 32bits
with "extrw,s".
So, only 16bits instead of 32bits are loaded from the address where "evil"
is...
next prev parent reply other threads:[~2021-09-01 21:25 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-01 16:52 [Bug tree-optimization/102162] New: " danglin at gcc dot gnu.org
2021-09-01 18:52 ` [Bug tree-optimization/102162] " danglin at gcc dot gnu.org
2021-09-01 20:14 ` arnd at linaro dot org
2021-09-01 20:52 ` deller at gmx dot de
2021-09-01 20:56 ` dave.anglin at bell dot net
2021-09-01 21:08 ` dave.anglin at bell dot net
2021-09-01 21:15 ` deller at gmx dot de
2021-09-01 21:19 ` dave.anglin at bell dot net
2021-09-01 21:25 ` deller at gmx dot de [this message]
2021-09-01 21:29 ` deller at gmx dot de
2021-09-01 21:48 ` pinskia at gcc dot gnu.org
2021-09-01 21:51 ` [Bug middle-end/102162] " pinskia at gcc dot gnu.org
2021-09-01 21:52 ` pinskia at gcc dot gnu.org
2021-09-01 22:35 ` dave.anglin at bell dot net
2021-09-01 22:46 ` dave.anglin at bell dot net
2021-09-01 22:56 ` pinskia at gcc dot gnu.org
2021-09-01 23:19 ` pinskia at gcc dot gnu.org
2021-09-01 23:21 ` pinskia at gcc dot gnu.org
2021-09-01 23:29 ` pinskia at gcc dot gnu.org
2021-09-01 23:45 ` pinskia at gcc dot gnu.org
2021-09-01 23:55 ` pinskia at gcc dot gnu.org
2021-09-02 0:02 ` dave.anglin at bell dot net
2021-09-02 0:19 ` pinskia at gcc dot gnu.org
2021-09-02 0:23 ` pinskia at gcc dot gnu.org
2021-09-02 0:47 ` dave.anglin at bell dot net
2021-09-02 0:49 ` pinskia at gcc dot gnu.org
2021-09-02 3:33 ` pinskia at gcc dot gnu.org
2021-09-02 7:12 ` rguenth at gcc dot gnu.org
2021-09-02 9:01 ` arnd at linaro dot org
2021-09-02 9:41 ` deller at gmx dot de
2021-09-02 9:52 ` pinskia at gcc dot gnu.org
2021-09-02 13:59 ` deller at gmx dot de
2021-09-02 14:00 ` deller at gmx dot de
2021-09-03 23:25 ` deller at gmx dot de
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