Incorrect function prologue with Thumb-1 high register variable

[Andrew Stubbs]

Compiling the following with "-Os -mthumb" results in the caller's r8 being incorrectly clobbered.

void foo(int x)
{
  register int foo asm("r8") = x;
  asm volatile ("@frob %0" :: "r"(foo);
}

GCC chooses not to use r8-r11 when optimizing Thumb-1 for size. However this should not be user-visible. Note that this is the correct behavior when the user specifies -ffixed-r8, care should be taken not the break that.

Discovered while trying to solve a different problem in eglibc.

[CodeSourcery Tracker ID #9085]

[Andrew Stubbs (ams-codesourcery)]

This is Thumb-1, so setting "low" importance.

[Michael Hope (michaelh1)]

Andrew, if this has been fixed by CSL then could you please merge it into gcc-linaro? Otherwise we should make sure this is reported upstream and decline this bug.

[Michael Hope (michaelh1)]

Andrew, any thoughts?

[Andrew Stubbs (ams-codesourcery)]

There's been no change to CSL bug #9085, so I doubt we've fixed this yet.

[Michael Collison (michael-collison)]

Not an issue with Linaro 4.8 or 4.9 as r8 is preserved. Will not fix for older releases.