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Re: reload getting the mode of (subreg:HI (reg:QI pseudo)) wrong

Rask Ingemann Lambertsen wrote: 
The constraints are not met because the constraint "d" is register class
DX_REGS consisting of register 4 and 5, and (reg:HI 5 dh) spans register 5
and 6. Also, HARD_REGNO_NREGS (5, HImode) returns 0.

The lreg and greg dumps provide the clue that reload got the mode wrong:

(insn:HI 2485 2483 2486 39 libgcc2.c:1825 (set (subreg:HI (reg:QI 178) 0)
	(ashiftrt:HI (reg:HI 641)
	    (const_int 15 [0xf]))) 31 {*ashrhi3_const15}
		(insn_list:REG_DEP_TRUE 2480 (nil))
    (expr_list:REG_DEAD (reg:HI 641)
	(nil)))

Probably the compiler doesn't in general like a paradoxical subreg that can take more hard regs than its SUBREG_REG. I think this is probably something that can be worked around with a proper combination of MODES_TIEABLE_P, CANNOT_CHANGE_MODE_CLASS, and maybe REG_CANNOT_CHANGE_MODE_P. What are your definitions of those macros?


Bernd

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