[Bug c/35069] New: Casting from a volatile type to a non-volatile type should cause a warning

[gcc-david at tulloh dot id dot au]

Given the following code:

volatile int16_t foo;
x = (int32_t)foo;

The above cast should almost certainly have been (volatile int32_t), I see no
obvious case where someone would want to cast away the volatile attribute.

I suggest that a cast that drops a volatile attribute from a variable should
cause a warning.


(Epiphany occurred at the end of a frustrating day, was using gcc 4.2.2
targeting an AVR)


-- 
   Summary: Casting from a volatile type to a non-volatile type
should cause a warning
   Product: gcc
   Version: 4.2.2
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: gcc-david at tulloh dot id dot au


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35069

[Bug c/35069] Casting from a volatile type to a non-volatile type should cause a warning

[gcc-david at tulloh dot id dot au]

-- 

gcc-david at tulloh dot id dot au changed:

   What|Removed |Added

   Severity|normal  |enhancement


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35069

[Bug c/35069] Casting from a volatile type to a non-volatile type should cause a warning

[gcc-david at tulloh dot id dot au]

--- Comment #2 from gcc-david at tulloh dot id dot au  2008-02-04 22:14 
---
Yes, I didn't provide any context.  I believe that this warning should apply
any time you are working with volatile variables.


A truncated real world example (kind of, real world debugging).

volatile static uint8_t OutputBuffer[4];

int16_t main(void) {
  while(1) {
*(uint16_t *)(OutputBuffer)++;
  }
}

ISR(PCINT0_vect) {
  implement software SPI interface, transmit OutputBuffer in reverse byte
order.
}


-- 

gcc-david at tulloh dot id dot au changed:

   What|Removed |Added

 Status|RESOLVED|UNCONFIRMED
 Resolution|INVALID |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35069

[Bug c/34736] New: AVR optimiser does not keep interrupt disabled blocks small

[gcc-david at tulloh dot id dot au]

I am compiling for an avr target and sharing variables with interrupts.  To
safely update the variables I am disabling interrupts but I want the interrupts
to be disabled for the shortest possible period of time.

The compiler shifts the instructions around slightly when optimizing, this has
the effect of increasing the time that interrupts are disabled.  I've attached
a trivial example which demonstrates this however more complicated code has a
similar result with a varying number of instructions moved into the disabled
section.


I'm attaching a trivial example with .c, .i (typedefs trimmed) and .s files.

The gcc used is from the Debian gcc-avr package version 4.2.2-1

Compilation line was:
avr-gcc -mmcu=attiny13 -Wall -Os -fsigned-char -S -c -o interrupt_disable_bug.s
interrupt_disable_bug.c


-- 
   Summary: AVR optimiser does not keep interrupt disabled blocks
small
   Product: gcc
   Version: 4.2.2
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: gcc-david at tulloh dot id dot au
GCC target triplet: AVR


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34736

[Bug c/34736] AVR optimiser does not keep interrupt disabled blocks small

[gcc-david at tulloh dot id dot au]

--- Comment #1 from gcc-david at tulloh dot id dot au  2008-01-11 06:04 
---
Created an attachment (id=14917)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14917&action=view)
Trivial example source file


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34736

[Bug c/34736] AVR optimiser does not keep interrupt disabled blocks small

[gcc-david at tulloh dot id dot au]

--- Comment #2 from gcc-david at tulloh dot id dot au  2008-01-11 06:05 
---
Created an attachment (id=14918)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14918&action=view)
Trivial example intermediate file


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34736

[Bug c/34736] AVR optimiser does not keep interrupt disabled blocks small

[gcc-david at tulloh dot id dot au]

--- Comment #3 from gcc-david at tulloh dot id dot au  2008-01-11 06:05 
---
Created an attachment (id=14919)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=14919&action=view)
Trivial example assembler output file


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34736