https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116244
Jeffrey A. Law <law at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2024-08-06
--- Comment #1 from Jeffrey A. Law <law at gcc dot gnu.org> ---
A lot of similarities to the most recent bug on the m68k.
We had this prior to ext-dce (from a somewhat reduced testcase, so insn #s
won't match):
(insn 878 877 881 19 (set (reg:DI 35 [ diff$__r ])
(zero_extend:DI (reg:SI 49 [ _32 ])))
"/notnfs/josmyers/glibc-manual/build/compilers/m68k-linux-gnu-coldfire/gcc/m68k-glibc-linux-gnu/libstdc++-v3/include/bits/chrono.h":574:10
85 {*zero_extendsidi2}
(expr_list:REG_DEAD (reg:SI 49 [ _32 ])
(nil)))
We know the upper bits aren't needed, so we turn the zero_extend into a subreg:
(insn 878 877 881 19 (set (reg:DI 35 [ diff$__r ])
(subreg:DI (reg:SI 49 [ _32 ]) 0))
"/notnfs/josmyers/glibc-manual/build/compilers/m68k-linux-gnu-coldfire/gcc/m68k-glibc-linux-gnu/libstdc++-v3/include/bits/chrono.h":574:10
76 {*m68k.md:1608}
(expr_list:REG_DEAD (reg:SI 49 [ _32 ])
(nil)))
So far, so good. We assign (reg:SI 49) to d0 resulting in this in the middle
of reload:
(insn 878 877 1042 19 (set (reg:DI 0 %d0 [orig:35 diff$__r ] [35])
(subreg:DI (reg:SI 0 %d0) 0))
"/notnfs/josmyers/glibc-manual/build/compilers/m68k-linux-gnu-coldfire/gcc/m68k-glibc-linux-gnu/libstdc++-v3/include/bits/chrono.h":574:10
76 {*m68k.md:1608}
(expr_list:REG_DEAD (reg:SI 0 %d0 [orig:49 _32 ] [49])
(nil)))
We eventually try to simplify the subreg resulting in:
(insn 878 877 1042 19 (set (reg:DI 0 %d0 [orig:35 diff$__r ] [35])
(reg:DI -1 [+-4 ]))
"/notnfs/josmyers/glibc-manual/build/compilers/m68k-linux-gnu-coldfire/gcc/m68k-glibc-linux-gnu/libstdc++-v3/include/bits/chrono.h":574:10
76 {*m68k.md:1608}
(nil))
Which is clearly very bad.
