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Re: Reload related segfaults


From: David Miller <davem@davemloft.net>
Date: Wed, 26 Oct 2011 23:07:11 -0400 (EDT)

> From: Alan Modra <amodra@gmail.com>
> Date: Thu, 27 Oct 2011 13:29:56 +1030
> 
>> Some recent patch has exposed a reload bug.  I'm seeing
> 
> I think this might be a side effect or Eric's recent changes,
> CC:'d.

Eric, I'm seeing a similar segmentation fault in reload on sparc64.
But it's in a slightly different place than Alan's crash.

Simply compile gcc.target/ultrasp12.c with "-m64 -O2 -mcpu=ultrasparc -mvis"
to see this.

The crash is in find_valid_class() called from push_reload(), via this
code block around line 1184 of reload.c:

      enum reg_class in_out_class
	= find_valid_class (outmode, GET_MODE (SUBREG_REG (out)),
			    subreg_regno_offset (REGNO (SUBREG_REG (out)),
						 GET_MODE (SUBREG_REG (out)),
						 SUBREG_BYTE (out),
						 GET_MODE (out)),
			    REGNO (SUBREG_REG (out)));

'out' is:

(subreg:DI (reg/v:V4QI 50 %f18 [orig:314 s2hi4_ ] [314]) 0)

so subreg_regno_offset() returns -1, and find_valid_class() isn't too happy
about getting "-1" for it's 'n' argument.

I suspect the test that you removed in order to fix rtl-optimization/46603
would guard against this happening.

And indeed, I confirmed that backing out the rtl-optimization/46603
fix makes the segmentation fault go away.


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