Add missed adjustment to label_nuses in reload.

Reload (find_reloads) has code that can replace a register with a 
label_ref when presented with RTL of the form:

(set (reg) (reg) (notes (rtx_equal (label_ref)))

Label references are initially counted in jump.c:mark_all_labels() and 
friends. This code traverses the RTL and counts each observed label_ref. 
The code inserts REG_LABEL_OPERAND or REG_LABEL_TARGET as appropriate. 
Notes are not traversed therefore the (rtx_equal (label_ref)) shown 
above is not treated as a reference.

Instruction deletion, in cfgrtl.c:delete_insn() does not re-traverse the 
RTL, The code traverses only the notes looking for REG_LABEL_OPERAND and 
REG_TARGET_OPERAND notes in order to count down the label_nuses field.

The code in reload.c:find_reloads() converts a register to a label_ref 
and inserts the associated REG_LABEL_OPERAND but does not adjust 
label_nuses, this may result in the inappropriate deletion of a live label.

This issue was discovered during the development of the ARM aarch64 gcc 
backend and results in an ICE due to deletion of a live jump table.

The issue has not been re-created on another target. The proposed patch 
has been regressed on x86 (and aarch64).

Proposed ChangeLog entry below, patch attached:

2012-01-04  Marcus Shawcroft  <marcus.shawcroft@arm.com>

	* reload.c (find_reloads): Adjust LABEL_NUSES on
	  REG_LABEL_OPERAND insertion.

/Marcus

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On 01/04/12 07:07, Marcus Shawcroft wrote:
> Reload (find_reloads) has code that can replace a register with a 
> label_ref when presented with RTL of the form:
> 
> (set (reg) (reg) (notes (rtx_equal (label_ref)))
> 
> Label references are initially counted in jump.c:mark_all_labels()
> and friends. This code traverses the RTL and counts each observed
> label_ref. The code inserts REG_LABEL_OPERAND or REG_LABEL_TARGET
> as appropriate. Notes are not traversed therefore the (rtx_equal
> (label_ref)) shown above is not treated as a reference.
> 
> Instruction deletion, in cfgrtl.c:delete_insn() does not
> re-traverse the RTL, The code traverses only the notes looking for
> REG_LABEL_OPERAND and REG_TARGET_OPERAND notes in order to count
> down the label_nuses field.
> 
> The code in reload.c:find_reloads() converts a register to a
> label_ref and inserts the associated REG_LABEL_OPERAND but does not
> adjust label_nuses, this may result in the inappropriate deletion
> of a live label.
> 
> This issue was discovered during the development of the ARM aarch64
> gcc backend and results in an ICE due to deletion of a live jump
> table.
> 
> The issue has not been re-created on another target. The proposed
> patch has been regressed on x86 (and aarch64).
> 
> Proposed ChangeLog entry below, patch attached:
> 
> 2012-01-04  Marcus Shawcroft  <marcus.shawcroft@arm.com>
> 
> * reload.c (find_reloads): Adjust LABEL_NUSES on REG_LABEL_OPERAND
> insertion.
Approved after you fix some minor fomatting nits. Your code has:

++ LABEL_NUSES(XEXP (substitution, 0));

The line should be:

++LABEL_NUSES (XEXP (substitution, 0));

No space between autoincrement operator and its operand.
Space before the open paren of the XEXP

Thanks,
Jeff
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