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PHIOPT: Mark the conditional lhs and rhs as to look at to see if DCEable

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In some cases (usually dealing with bools only), there could be some statements
left behind which are considered trivial dead.
An example is:
```
bool f(bool a, bool b)
{
    if (!a && !b)
        return 0;
    if (!a && b)
        return 0;
    if (a && !b)
        return 0;
    return 1;
}
```
Where during phiopt2, the IR had:
```
  _3 = ~b_7(D);
  _4 = _3 & a_6(D);
  _4 != 0 ? 0 : 1
```
match-and-simplify would transform that into:
```
  _11 = ~a_6(D);
  _12 = b_7(D) | _11;
```
But phiopt would leave around the statements defining _4 and _3.
This helps by marking the conditional's lhs and rhs to see if they are
trivial dead.

OK? Bootstrapped and tested on x86_64-linux-gnu.

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (match_simplify_replacement): Mark's cond
	statement's lhs and rhs to check if trivial dead.
	Rename inserted_exprs to exprs_maybe_dce; also move it so
	bitmap is not allocated if not needed.
This commit is contained in:
Andrew Pinski 2023-06-13 09:17:45 -07:00
parent 21c2815605
commit 7ff1d1b156
1 changed files with 16 additions and 5 deletions
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21
gcc/tree-ssa-phiopt.cc
View file

@ -767,7 +767,6 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
tree result;
gimple *stmt_to_move = NULL;
gimple *stmt_to_move_alt = NULL;
auto_bitmap inserted_exprs;
tree arg_true, arg_false;
/* Special case A ? B : B as this will always simplify to B. */
@ -844,6 +843,18 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
if (!result)
return false;
auto_bitmap exprs_maybe_dce;
/* Mark the cond statements' lhs/rhs as maybe dce. */
if (TREE_CODE (gimple_cond_lhs (stmt)) == SSA_NAME
&& !SSA_NAME_IS_DEFAULT_DEF (gimple_cond_lhs (stmt)))
bitmap_set_bit (exprs_maybe_dce,
SSA_NAME_VERSION (gimple_cond_lhs (stmt)));
if (TREE_CODE (gimple_cond_rhs (stmt)) == SSA_NAME
&& !SSA_NAME_IS_DEFAULT_DEF (gimple_cond_rhs (stmt)))
bitmap_set_bit (exprs_maybe_dce,
SSA_NAME_VERSION (gimple_cond_rhs (stmt)));
gsi = gsi_last_bb (cond_bb);
/* Insert the sequence generated from gimple_simplify_phiopt. */
if (seq)
@ -855,7 +866,7 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
gimple *stmt = gsi_stmt (gsi1);
tree name = gimple_get_lhs (stmt);
if (name && TREE_CODE (name) == SSA_NAME)
bitmap_set_bit (inserted_exprs, SSA_NAME_VERSION (name));
bitmap_set_bit (exprs_maybe_dce, SSA_NAME_VERSION (name));
}
if (dump_file && (dump_flags & TDF_FOLDING))
{
@ -867,10 +878,10 @@ match_simplify_replacement (basic_block cond_bb, basic_block middle_bb,
/* If there was a statement to move, move it to right before
the original conditional. */
move_stmt (stmt_to_move, &gsi, inserted_exprs);
move_stmt (stmt_to_move_alt, &gsi, inserted_exprs);
move_stmt (stmt_to_move, &gsi, exprs_maybe_dce);
move_stmt (stmt_to_move_alt, &gsi, exprs_maybe_dce);
replace_phi_edge_with_variable (cond_bb, e1, phi, result, inserted_exprs);
replace_phi_edge_with_variable (cond_bb, e1, phi, result, exprs_maybe_dce);
/* Add Statistic here even though replace_phi_edge_with_variable already
does it as we want to be able to count when match-simplify happens vs