https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78378
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
So we have:
(insn 6 3 7 2 (parallel [
(set (reg/v:DI 90 [ x ])
(ashift:DI (reg/v:DI 93 [ x ])
(const_int 41 [0x29])))
(clobber (reg:CC 17 flags))
]) "pr78378.c":7 530 {*ashldi3_1}
(expr_list:REG_DEAD (reg/v:DI 93 [ x ])
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil))))
(insn 7 6 8 2 (parallel [
(set (reg:DI 96)
(lshiftrt:DI (reg/v:DI 90 [ x ])
(const_int 3 [0x3])))
(clobber (reg:CC 17 flags))
]) "pr78378.c":8 564 {*lshrdi3_1}
(expr_list:REG_DEAD (reg/v:DI 90 [ x ])
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil))))
(insn 8 7 9 2 (set (reg:DI 98)
(const_int 636094623231363849 [0x8d3dcb08d3dcb09])) "pr78378.c":8 81
{*movdi_internal}
(nil))
(insn 9 8 10 2 (parallel [
(set (reg:DI 97 [ x ])
(truncate:DI (lshiftrt:TI (mult:TI (zero_extend:TI (reg:DI 96))
(zero_extend:TI (reg:DI 98)))
(const_int 64 [0x40]))))
(clobber (scratch:DI))
(clobber (reg:CC 17 flags))
]) "pr78378.c":8 342 {*umuldi3_highpart_1}
(expr_list:REG_DEAD (reg:DI 98)
(expr_list:REG_DEAD (reg:DI 96)
(expr_list:REG_UNUSED (reg:CC 17 flags)
(expr_list:REG_EQUAL (truncate:DI (lshiftrt:TI (mult:TI
(zero_extend:TI (reg:DI 96))
(const_int 636094623231363849
[0x8d3dcb08d3dcb09]))
(const_int 64 [0x40])))
(nil))))))
and I think the bug is already when substing (reg:DI 98) to (const_int
636094623231363849 [0x8d3dcb08d3dcb09]), because we turn it into:
(set (reg:DI 97 [ x ])
(subreg:DI (mult:TI (zero_extend:TI (reg:DI 96))
(const_int 636094623231363849 [0x8d3dcb08d3dcb09])) 8))
the right shift by 64 around mult is lost, so it is no longer high part
multiply, but lowpart multiply.
