[Bug inline-asm/78487] asm cpuid code and -fgcse crashes

[s-beyer at gmx dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78487

Stephan Beyer  changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution|--- |INVALID

--- Comment #6 from Stephan Beyer  ---
Ok, the problem is solved using __get_cpuid(). Sorry for bothering you and
thank you for the quick help.

[Bug inline-asm/78487] asm cpuid code and -fgcse crashes

[s-beyer at gmx dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78487

--- Comment #5 from Stephan Beyer  ---
It crashes on run-time.

I have absolutely no experience using extended asm syntax but I
guess g++ relies on the constraints for its optimization, so I
guess the constraints are wrong.

I will port the code to use the macro from cpuid.h and close the
issue if there are no more crashes.

Thank you.

[Bug inline-asm/78487] asm cpuid code and -fgcse crashes

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78487

--- Comment #4 from Andrew Pinski  ---
Also I doubt this code is correct.

[Bug inline-asm/78487] asm cpuid code and -fgcse crashes

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78487

--- Comment #3 from Andrew Pinski  ---
Crashes at runtime or crashes inside GCC?

[Bug inline-asm/78487] asm cpuid code and -fgcse crashes

[s-beyer at gmx dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78487

--- Comment #2 from Stephan Beyer  ---
The following problem is only reproducible on one machine.
I cannot reproduce it on any other machine.

When compiling the attached C++ source file with
g++ -O1 -fgcse, it crashes at the third cpuid call (ie,
there are three output lines).
When just using g++ -O1 (without -fgcse), it works well.

Changing the code in main() slightly or making cpuid() inline
makes it work well also with -fgcse.

uname -a and g++ --version of that machine says:

Linux ipc675 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt4-3 (2015-02-03) x86_64
GNU/Linux

g++ (Debian 6.2.0-13) 6.2.0 20161109

If useful, I can also attach assembly output of the crashing code (with
-fgcse),
of the code without -fgcse and of the code with "inline" (there using
-fgcse makes no difference).

The code is not written by me, so I don't know if its "correct" or if
the input/output asm constraints are just used wrong.
(It's just the minimal example I got from code where a crash occurred.)

PS: excuse the first empty bug report, it seems I am too
stupid for bugzilla.

[Bug inline-asm/78487] asm cpuid code and -fgcse crashes

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78487

--- Comment #1 from Andrew Pinski  ---
What is the error message which you are getting?  

Here is how GCC's cpuid.h header look like for cpuid:

#define __cpuid(level, a, b, c, d)  \
  __asm__ ("cpuid\n\t"  \
   : "=a" (a), "=b" (b), "=c" (c), "=d" (d) \
   : "0" (level))

#define __cpuid_count(level, count, a, b, c, d) \
  __asm__ ("cpuid\n\t"  \
   : "=a" (a), "=b" (b), "=c" (c), "=d" (d) \
   : "0" (level), "2" (count))


It does not use r but rather b directly.