[patch] Fix GC issue triggered by arithmetic overflow checking

Eric Botcazou ebotcazou@adacore.com
Thu Oct 13 10:16:00 GMT 2016


> Yes.  But that's not the only source for DECL_UID differences.  Btw,
> I see lots of FOR_EACH_HASH_TABLE_ELEMENT in var-tracking.c
> but they don't look like their outcome is supposed to be dependent on
> element ordering.

This leads to NOTE_INSN_VAR_LOCATION notes emitted in a different order, which 
are then interpreted by dwarf2out_var_location.  In particular:

(note 6350 6349 6351 (var_location temp (nil)) NOTE_INSN_VAR_LOCATION)
(note 6351 6350 6352 (var_location temp$low (mem/c:DI (plus:SI (reg/f:SI 30 
%fp)
        (const_int -112 [0xffffffffffffff90])) [10 MEM[(struct cpp_num 
*)&result + 8B]+0 S8 A64])) NOTE_INSN_VAR_LOCATION)
(note 6352 6351 6353 (var_location temp$8 (nil)) NOTE_INSN_VAR_LOCATION)
[...]
(code_label 2091 6355 2092 79 912 "" [1 uses])
(note 2092 2091 5271 79 [bb 79] NOTE_INSN_BASIC_BLOCK)

is interpreted differently from:

(note 6350 6349 6351 (var_location temp (nil)) NOTE_INSN_VAR_LOCATION)
(note 6351 6350 6352 (var_location temp$8 (nil)) NOTE_INSN_VAR_LOCATION)
(note 6352 6351 6353 (var_location temp$low (mem/c:DI (plus:SI (reg/f:SI 30 
%fp)
        (const_int -112 [0xffffffffffffff90])) [10 MEM[(struct cpp_num 
*)&result + 8B]+0 S8 A64])) NOTE_INSN_VAR_LOCATION)
[...]
(note 2092 2091 5271 79 [bb 79] NOTE_INSN_BASIC_BLOCK)

@@ -32608,6 +32608,17 @@
 	.uleb128 0x8
 	.byte	0x93	! DW_OP_piece
 	.uleb128 0x8
+	.uaword	.LLVL592-.LLtext0	! Location list begin address 
(*.LLLST153)
+	.uaword	.LLVL597-.LLtext0	! Location list end address 
(*.LLLST153)
+	.uahalf	0x9	! Location expression size
+	.byte	0x93	! DW_OP_piece
+	.uleb128 0x8
+	.byte	0x8e	! DW_OP_breg30
+	.sleb128 -112
+	.byte	0x93	! DW_OP_piece
+	.uleb128 0x8
+	.byte	0x93	! DW_OP_piece
+	.uleb128 0x8
 	.uaword	.LLVL695-.LLtext0	! Location list begin address 
(*.LLLST153)
 	.uaword	.LLVL696-.LLtext0	! Location list end address 
(*.LLLST153)
 	.uahalf	0xe	! Location expression size

probably because the non-null location comes last in the second case.

-- 
Eric Botcazou



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