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Re: [PATCH] Remove also 2nd argument for unused delete operator (PR tree-optimization/91270).
On 7/29/19 11:59 AM, Richard Biener wrote:
> On Sun, Jul 28, 2019 at 4:57 PM Martin Liška <firstname.lastname@example.org> wrote:
>> And there's one more patch that deals with delete operator
>> which has a second argument (size). That definition GIMPLE
>> statement of the size must be also properly marked.
>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
>> Ready to be installed?
> This isn't a proper fix. You can't mark a random operand as necessary
> during elimination - this only works in very constraint cases. Here
> it will break down if the stmt you just marked depends on another stmt
> only used by the stmt you just marked (and thus also not necessary).
Ah, I see.
> The fix is to propagate_necessity where you either have to excempt
> the two-operator delete from handling
We want to process also these delete operators.
> or to mark its second operand
> as necessary despite eventually deleting the call.
Really marking that as necessary? Why?
> You can avoid
> this in case the allocation function used the exact same size argument.
That's not the case as the operator new happens in a loop:
<bb 5> :
# iftmp.0_15 = PHI <iftmp.0_21(3), iftmp.0_20(4)>
_23 = operator new  (iftmp.0_15);
_24 = _23;
MEM[(sizetype *)_24] = _19;
_26 = _24 + 8;
_27 = _26;
_2 = _19 + 18446744073709551615;
_28 = (long int) _2;
<bb 6> :
# _12 = PHI <_27(5), _29(7)>
# _13 = PHI <_28(5), _30(7)>
if (_13 < 0)
goto <bb 8>; [INV]
goto <bb 7>; [INV]
Btw. is the hunk moved to propagate_necessity still wrong:
diff --git a/gcc/tree-ssa-dce.c b/gcc/tree-ssa-dce.c
index cf507fa0453..1c890889932 100644
@@ -803,7 +803,23 @@ propagate_necessity (bool aggressive)
|| DECL_FUNCTION_CODE (def_callee) == BUILT_IN_MALLOC
|| DECL_FUNCTION_CODE (def_callee) == BUILT_IN_CALLOC))
|| DECL_IS_REPLACEABLE_OPERATOR_NEW_P (def_callee)))
+ /* Some delete operators have 2 arguments, where
+ the second argument is size of the deallocated memory. */
+ if (gimple_call_num_args (stmt) == 2)
+ tree ptr = gimple_call_arg (stmt, 1);
+ if (TREE_CODE (ptr) == SSA_NAME)
+ gimple *def_stmt = SSA_NAME_DEF_STMT (ptr);
+ if (!gimple_nop_p (def_stmt)
+ && !gimple_plf (def_stmt, STMT_NECESSARY))
+ gimple_set_plf (stmt, STMT_NECESSARY, false);
FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_USE)