[Bug target/71053] [6/7 Regression] Volatile read optimized into endless loop

["bseifert at gmx dot at" <gcc-bugzilla@gcc.gnu.org>]

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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71053

Berni <bseifert at gmx dot at> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bseifert at gmx dot at

--- Comment #3 from Berni <bseifert at gmx dot at> ---
I also reproduced the bug after building the avr gcc 6.1.0 tool chain.

if you wait for the ADC to complete a measurement, you use the following code:

while (ADCSRA & _BV(ADSC));

which looks like the following after the post processor:

while ((*(volatile uint8_t *)(0x7A)) & (1 << (6)));

which looks fine, but it compiles to:

    3c38:       80 91 7a 00     lds     r24, 0x007A
    3c3c:       80 74           andi    r24, 0x40       ; 64
    3c3e:       81 11           cpse    r24, r1
    3c40:       fe cf           rjmp    .-4             ; 0x3c3e <main+0x12>

this is an endless loop. It does not respect the volatile keyword.
>From gcc-bugs-return-524919-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu May 12 09:51:19 2016
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Date: Thu, 12 May 2016 09:51:00 -0000
From: Kyrill Tkachov <kyrylo.tkachov@foss.arm.com>
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To: RaghuShankar <mcsraghu@gmail.com>, gcc-bugs@gcc.gnu.org
Subject: Re: GCC 6.1.0 ARM cross compiling xgcc error not producing output file from .S files
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Hi,

On 12/05/16 10:46, RaghuShankar wrote:
> Hi,
>
> I am trying to cross compile the latest gcc 6.1.0 to arm architecture.
>
> At the end of libgcc compilation i am getting the error
> *"root/embeddedlinux/gcc/armcrosstool/arm-linux-gnueabi/bin/ar:
> _thumb1_case_sqi.o: No such file or directory"*
>
> *But when i cross checked libgcc compilation it has compiled the
> "_thumb1_case_sqi.dep" file and tried to create .o file but it is not? Hence
> the error.*
>
> /root/embeddedlinux/gcc/gcc-6.1.0/build/./gcc/xgcc
> -B/root/embeddedlinux/gcc/gcc-6.1.0/build/./gcc/
> -B/root/embeddedlinux/gcc/armcrosstool/arm-linux-gnueabi/bin/
> -B/root/embeddedlinux/gcc/armcrosstool/arm-linux-gnueabi/lib/ -isystem
> /root/embeddedlinux/gcc/armcrosstool/arm-linux-gnueabi/include -isystem
> /root/embeddedlinux/gcc/armcrosstool/arm-linux-gnueabi/sys-include    -g -O2
> -O2  -g -O2 -DIN_GCC  -DCROSS_DIRECTORY_STRUCTURE  -W -Wall -Wno-narrowing
> -Wwrite-strings -Wcast-qual -Wstrict-prototypes -Wmissing-prototypes
> -Wold-style-definition  -isystem ./include   -fPIC -fno-inline -g
> -DIN_LIBGCC2 -fbuilding-libgcc -fno-stack-protector -Dinhibit_libc  -fPIC
> -fno-inline   -DUSE_EMUTLS -o _thumb1_case_sqi.o -MT _thumb1_case_sqi.o -MD
> -MP -MF _thumb1_case_sqi.dep -DL_thumb1_case_sqi -xassembler-with-cpp -c
> ../../../libgcc/config/arm/lib1funcs.S -include _thumb1_case_sqi.vis
>
> For further error information please check the attached error file.
> gcc-6.txt <http://gcc.1065356.n5.nabble.com/file/n1262876/gcc-6.txt>
>
> If any body having solution please let us know.

This list is for the automatic emails generated by the GCC bug tracker.
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Try gcc-help@gcc.gnu.org.

If you think you have found a bug in GCC please report it according to the
instructions at https://gcc.gnu.org/bugs/

Cheers,
Kyrill

> Thanking you
>
>
>
>
>
>
> --
> View this message in context: http://gcc.1065356.n5.nabble.com/GCC-6-1-0-ARM-cross-compiling-xgcc-error-not-producing-output-file-from-S-files-tp1262876.html
> Sent from the gcc - bugs mailing list archive at Nabble.com.
>