After register allocation we have no idea where GOT address is and
therefore delegitimize_address target hook becomes less efficient and
cannot remove UNSPECs. That's what I see now when build GCC with patch
applied:
In theory this shouldn't be too hard to fix.
I haven't looked at the code, but it might be something looking explicitly
for ebx by register #, or something similar. Which case within
delegitimize_address isn't firing as it should after your changes?
It is the case I had to fix:
@@ -14415,7 +14433,8 @@ ix86_delegitimize_address (rtx x)
...
movl foo@GOTOFF(%ecx), %edx
in which case we return (%ecx - %ebx) + foo. */
- if (pic_offset_table_rtx)
+ if (pic_offset_table_rtx
+ && (!reload_completed || !ix86_use_pseudo_pic_reg ()))
result = gen_rtx_PLUS (Pmode, gen_rtx_MINUS (Pmode, copy_rtx (addend),
pic_offset_table_rtx),
result);
Originally if there is a UNSPEC_GOTOFFSET but no EBX usage then we
just remove this UNSPEC and substract EBX value. With pseudo PIC reg
we should use PIC register instead of EBX but it is unclear what to
use after register allocation.