From patchwork Wed Jan  4 14:07:52 2012
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Subject: Add missed adjustment to label_nuses in reload.
Date: Wed, 04 Jan 2012 04:07:52 -0000
From: Marcus Shawcroft <marcus.shawcroft@arm.com>
X-Patchwork-Id: 134254
Message-Id: <4F045D38.7060204@arm.com>
To: gcc-patches@gcc.gnu.org

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


diff --git a/gcc/reload.c b/gcc/reload.c
index 53dcd2d..206fb36 100644
--- a/gcc/reload.c
+++ b/gcc/reload.c
@@ -4212,7 +4212,12 @@ find_reloads (rtx insn, int replace, int ind_levels, int live_known,
 	      && (!JUMP_P (insn)
 		  || !label_is_jump_target_p (XEXP (substitution, 0),
 					      insn)))
-	    add_reg_note (insn, REG_LABEL_OPERAND, XEXP (substitution, 0));
+	    {
+	      add_reg_note (insn, REG_LABEL_OPERAND, XEXP (substitution, 0));
+	      if (LABEL_P (XEXP (substitution, 0)))
+		++ LABEL_NUSES(XEXP (substitution, 0));
+	    }
+
 	}
       else
 	retval |= (substed_operand[i] != *recog_data.operand_loc[i]);