Hi Richard,
On 25 August 2016 at 22:24, Richard Biener <richard.guent...@gmail.com> wrote:
> On Thu, Aug 11, 2016 at 1:09 AM, kugan
> <kugan.vivekanandara...@linaro.org> wrote:
>> Hi,
>>
>>
>> On 10/08/16 20:28, Richard Biener wrote:
>>>
>>> On Wed, Aug 10, 2016 at 10:57 AM, Jakub Jelinek <ja...@redhat.com> wrote:
>>>>
>>>> On Wed, Aug 10, 2016 at 08:51:32AM +1000, kugan wrote:
>>>>>
>>>>> I see it now. The problem is we are just looking at (-1) being in the
>>>>> ops
>>>>> list for passing changed to rewrite_expr_tree in the case of
>>>>> multiplication
>>>>> by negate. If we have combined (-1), as in the testcase, we will not
>>>>> have
>>>>> the (-1) and will pass changed=false to rewrite_expr_tree.
>>>>>
>>>>> We should set changed based on what happens in try_special_add_to_ops.
>>>>> Attached patch does this. Bootstrap and regression testing are ongoing.
>>>>> Is
>>>>> this OK for trunk if there is no regression.
>>>>
>>>>
>>>> I think the bug is elsewhere. In particular in
>>>> undistribute_ops_list/zero_one_operation/decrement_power.
>>>> All those look problematic in this regard, they change RHS of statements
>>>> to something that holds a different value, while keeping the LHS.
>>>> So, generally you should instead just add a new stmt next to the old one,
>>>> and adjust data structures (replace the old SSA_NAME in some ->op with
>>>> the new one). decrement_power might be a problem here, dunno if all the
>>>> builtins are const in all cases that DSE would kill the old one,
>>>> Richard, any preferences for that? reset flow sensitive info + reset
>>>> debug
>>>> stmt uses, or something different? Though, replacing the LHS with a new
>>>> anonymous SSA_NAME might be needed too, in case it is before SSA_NAME of
>>>> a
>>>> user var that doesn't yet have any debug stmts.
>>>
>>>
>>> I'd say replacing the LHS is the way to go, with calling the appropriate
>>> helper
>>> on the old stmt to generate a debug stmt for it / its uses (would need
>>> to look it
>>> up here).
>>>
>>
>> Here is an attempt to fix it. The problem arises when in
>> undistribute_ops_list, we linearize_expr_tree such that NEGATE_EXPR is added
>> (-1) MULT_EXPR (OP). Real problem starts when we handle this in
>> zero_one_operation. Unlike what was done earlier, we now change the stmt
>> (with propagate_op_to_signle use or by directly) such that the value
>> computed by stmt is no longer what it used to be. Because of this, what is
>> computed in undistribute_ops_list and rewrite_expr_tree are also changed.
>>
>> undistribute_ops_list already expects this but rewrite_expr_tree will not if
>> we dont pass the changed as an argument.
>>
>> The way I am fixing this now is, in linearize_expr_tree, I set ops_changed
>> to true if we change NEGATE_EXPR to (-1) MULT_EXPR (OP). Then when we call
>> zero_one_operation with ops_changed = true, I replace all the LHS in
>> zero_one_operation with the new SSA and replace all the uses. I also call
>> the rewrite_expr_tree with changed = false in this case.
>>
>> Does this make sense? Bootstrapped and regression tested for
>> x86_64-linux-gnu without any new regressions.
>
> I don't think this solves the issue. zero_one_operation associates the
> chain starting at the first *def and it will change the intermediate values
> of _all_ of the stmts visited until the operation to be removed is found.
> Note that this is independent of whether try_special_add_to_ops did anything.
>
> Even for the regular undistribution cases we get this wrong.
>
> So we need to back-track in zero_one_operation, replacing each LHS
> and in the end the op in the opvector of the main chain. That's basically
> the same as if we'd do a regular re-assoc operation on the sub-chains.
> Take their subops, simulate zero_one_operation by
> appending the cancelling operation and optimizing the oplist, and then
> materializing the associated ops via rewrite_expr_tree.
>
Here is a draft patch which records the stmt chain when in
zero_one_operation and then fixes it when OP is removed. when we
update *def, that will update the ops vector. Does this looks sane?
Bootstrapped and regression tested on x86_64-linux-gnu with no new regressions.
Thanks,
Kugan
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr72835.c
b/gcc/testsuite/gcc.dg/tree-ssa/pr72835.c
index e69de29..049eddc 100644
--- a/gcc/testsuite/gcc.dg/tree-ssa/pr72835.c
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr72835.c
@@ -0,0 +1,36 @@
+/* PR tree-optimization/72835. */
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+struct struct_1 {
+ unsigned int m1 : 6 ;
+ unsigned int m2 : 24 ;
+ unsigned int m3 : 6 ;
+};
+
+unsigned short var_32 = 0x2d10;
+
+struct struct_1 s1;
+
+void init ()
+{
+ s1.m1 = 4;
+ s1.m2 = 0x7ca4b8;
+ s1.m3 = 24;
+}
+
+void foo ()
+{
+ unsigned int c
+ = ((unsigned int) s1.m2) * (-((unsigned int) s1.m3))
+ + (var_32) * (-((unsigned int) (s1.m1)));
+ if (c != 4098873984)
+ __builtin_abort ();
+}
+
+int main ()
+{
+ init ();
+ foo ();
+ return 0;
+}
diff --git a/gcc/tree-ssa-reassoc.c b/gcc/tree-ssa-reassoc.c
index 7fd7550..c7f6a66 100644
--- a/gcc/tree-ssa-reassoc.c
+++ b/gcc/tree-ssa-reassoc.c
@@ -1148,6 +1148,49 @@ decrement_power (gimple *stmt)
}
}
+/* Replace SSA defined by STMT and replace all its uses with new
+ SSA. Also return the new SSA. */
+
+static tree
+make_new_ssa_for_def (gimple *stmt)
+{
+ gimple *use_stmt;
+ use_operand_p use;
+ imm_use_iterator iter;
+ tree new_lhs;
+ tree lhs = gimple_assign_lhs (stmt);
+ gcc_assert (has_single_use (lhs));
+
+ new_lhs = make_ssa_name (TREE_TYPE (lhs));
+ gimple_set_lhs (stmt, new_lhs);
+
+ /* Also need to update GIMPLE_DEBUGs. */
+ FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs)
+ {
+ FOR_EACH_IMM_USE_ON_STMT (use, iter)
+ SET_USE (use, new_lhs);
+ update_stmt (use_stmt);
+ }
+ return new_lhs;
+}
+
+/* Replace all SSAs defined in STMTS_TO_FIX and replace its
+ uses with new SSAs. Also do this for the stmt that defines DEF
+ if *DEF is not OP. */
+
+static void
+make_new_ssa_for_all_defs (tree *def, tree op,
+ auto_vec<gimple *> &stmts_to_fix)
+{
+ unsigned i;
+ gimple *stmt = SSA_NAME_DEF_STMT (*def);
+ if (*def != op
+ && gimple_code (stmt) != GIMPLE_NOP)
+ *def = make_new_ssa_for_def (stmt);
+ FOR_EACH_VEC_ELT (stmts_to_fix, i, stmt)
+ make_new_ssa_for_def (stmt);
+}
+
/* Find the single immediate use of STMT's LHS, and replace it
with OP. Remove STMT. If STMT's LHS is the same as *DEF,
replace *DEF with OP as well. */
@@ -1186,6 +1229,9 @@ static void
zero_one_operation (tree *def, enum tree_code opcode, tree op)
{
gimple *stmt = SSA_NAME_DEF_STMT (*def);
+ /* PR72835 - Record the stmt chain that has to be updated such that
+ we dont use the same LHS when the values computed are different. */
+ auto_vec<gimple *> stmts_to_fix;
do
{
@@ -1195,6 +1241,7 @@ zero_one_operation (tree *def, enum tree_code opcode,
tree op)
{
if (stmt_is_power_of_op (stmt, op))
{
+ make_new_ssa_for_all_defs (def, op, stmts_to_fix);
if (decrement_power (stmt) == 1)
propagate_op_to_single_use (op, stmt, def);
return;
@@ -1204,6 +1251,7 @@ zero_one_operation (tree *def, enum tree_code opcode,
tree op)
if (gimple_assign_rhs1 (stmt) == op)
{
tree cst = build_minus_one_cst (TREE_TYPE (op));
+ make_new_ssa_for_all_defs (def, op, stmts_to_fix);
propagate_op_to_single_use (cst, stmt, def);
return;
}
@@ -1212,6 +1260,7 @@ zero_one_operation (tree *def, enum tree_code opcode,
tree op)
{
gimple_assign_set_rhs_code
(stmt, TREE_CODE (gimple_assign_rhs1 (stmt)));
+ make_new_ssa_for_all_defs (def, op, stmts_to_fix);
return;
}
}
@@ -1228,6 +1277,7 @@ zero_one_operation (tree *def, enum tree_code opcode,
tree op)
{
if (name == op)
name = gimple_assign_rhs2 (stmt);
+ make_new_ssa_for_all_defs (def, op, stmts_to_fix);
propagate_op_to_single_use (name, stmt, def);
return;
}
@@ -1243,6 +1293,8 @@ zero_one_operation (tree *def, enum tree_code opcode,
tree op)
gimple *stmt2 = SSA_NAME_DEF_STMT (gimple_assign_rhs2 (stmt));
if (stmt_is_power_of_op (stmt2, op))
{
+ stmts_to_fix.safe_push (stmt2);
+ make_new_ssa_for_all_defs (def, op, stmts_to_fix);
if (decrement_power (stmt2) == 1)
propagate_op_to_single_use (op, stmt2, def);
return;
@@ -1253,14 +1305,18 @@ zero_one_operation (tree *def, enum tree_code opcode,
tree op)
if (gimple_assign_rhs1 (stmt2) == op)
{
tree cst = build_minus_one_cst (TREE_TYPE (op));
+ stmts_to_fix.safe_push (stmt2);
+ make_new_ssa_for_all_defs (def, op, stmts_to_fix);
propagate_op_to_single_use (cst, stmt2, def);
return;
}
else if (integer_minus_onep (op)
|| real_minus_onep (op))
{
+ stmts_to_fix.safe_push (stmt2);
gimple_assign_set_rhs_code
(stmt2, TREE_CODE (gimple_assign_rhs1 (stmt2)));
+ make_new_ssa_for_all_defs (def, op, stmts_to_fix);
return;
}
}
@@ -1270,6 +1326,7 @@ zero_one_operation (tree *def, enum tree_code opcode,
tree op)
gcc_assert (name != op
&& TREE_CODE (name) == SSA_NAME);
stmt = SSA_NAME_DEF_STMT (name);
+ stmts_to_fix.safe_push (stmt);
}
while (1);
}
