https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66563
--- Comment #29 from Kazumoto Kojima <kkojima at gcc dot gnu.org> ---
I've reproduced one problem for mpfr-3.1.3 with the cross
compiler. For some TLS variables, we need to set GOT address
to the PIC register R12 even in non-PIC objects. Here is
a hypothetical example what is going on. Assume that we
computed GOT address twice in a function:
mova 1f,r0
mov.l 1f,r12
add r0,r12
...
1: .long _GLOBAL_OFFSET_TABLE_ ! GOTPC relocation
...
mova 2f,r0
mov.l 2f,r12
add r0,r12
...
2: .long _GLOBAL_OFFSET_TABLE_ ! GOTPC relocation
GOTPC relocation means that the value should set to (GOT address - .)
by linker.
Unfortunately, 4.9 and later compilers 'optimize' the above code
to the code like
mova 1f,r0
mov.l 1f,r12
mov r12,r11
add r0,r12
...
1: .long _GLOBAL_OFFSET_TABLE_ ! GOTPC relocation
...
mova 2f,r0
mov.l r11,r12
add r0,r12
...
2: .long _GLOBAL_OFFSET_TABLE_ ! GOTPC relocation
i.e. try to memoize the _GLOBAL_OFFSET_TABLE_ 'value'. This doesn't
work because the 2nd computation gets (GOT address - 1f) + 2f
instead of the correct GOT address. This issue will affect the non-PIC
objects which use TLS aggressively.
