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

[bseifert at gmx dot at]

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

Berni <bseifert at gmx dot at> changed:

           What    |Removed                     |Added
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                 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.