[Patch, regcprop] Tentative fix for PR 64331

Hi, The cprop_hardreg pass does not consider REG_DEAD notes when propagating, and this causes issues if target specific code uses dead_or_set_regno_p to know if it can clobber registers. For example, regcrop transforms (insn 7 4 8 2 (set (reg:SI 16 r16 [orig:43 D.1617 ] [43])

Re: [Patch, regcprop] Tentative fix for PR 64331

The cprop_hardreg pass does not consider REG_DEAD notes when propagating, and this causes issues if target specific code uses dead_or_set_regno_p to know if it can clobber registers. As explained in the audit trail, it doesn't have to. Killing regs that are marked REG_DEAD fixes the