[Bug inline-asm/91111] [7/8 Regression] arm64 Linux kernel panics at boot due to unexpected register assignment in inline asm

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91111

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jakub at gcc dot gnu.org

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Bisection shows that on the trunk before r264897 we emit:
 casal  x30, x1, [x0]
starting with r264897 we ICE and finally starting with r265398 we emit:
 casal  x30, x0, [x1]
The problem obviously is that combine propagates the hard register into the
memory, so we have
                        (reg/v:DI 0 x0 [orig:94 x0 ] [94])
                        (mem:DI (reg:DI 0 x0 [ v ]) [6 v_2(D)->counter+0 S8
A64])
as the outputs and IRA/LRA doesn't know what should be honored in that case
because it can't honor both.
Note, "Q" constraint is requesting a MEM that has a register operand.
r265398 is certainly not backportable to 8.x or earlier, it had some many
follow-ups that it is out of question.