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rewrite undefined overflow to defined in ifcombine

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When we make stmts to execute unconditionally in ifcombine we have
to make sure to rewrite stmts that can invoke undefined behavior
on overflow into a form with defined overflow.  That's possible
for all but signed division for which we have to avoid the transform.

2022-04-04  Richard Biener  <rguenther@suse.de>

	* tree-ssa-ifcombine.cc (bb_no_side_effects_p): Avoid executing
	divisions with undefined overflow unconditionally.
	(pass_tree_ifcombine::execute): Rewrite stmts with undefined
	overflow to defined.
This commit is contained in:
Richard Biener 2022-04-04 11:29:14 +02:00
parent 000f448000
commit c2a0d2e6f6
1 changed files with 29 additions and 0 deletions
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29
gcc/tree-ssa-ifcombine.cc
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@ -125,10 +125,26 @@ bb_no_side_effects_p (basic_block bb)
if (is_gimple_debug (stmt))
continue;
gassign *ass;
enum tree_code rhs_code;
if (gimple_has_side_effects (stmt)
|| gimple_uses_undefined_value_p (stmt)
|| gimple_could_trap_p (stmt)
|| gimple_vuse (stmt)
/* We need to rewrite stmts with undefined overflow to use
unsigned arithmetic but cannot do so for signed division. */
|| ((ass = dyn_cast <gassign *> (stmt))
&& INTEGRAL_TYPE_P (TREE_TYPE (gimple_assign_lhs (ass)))
&& TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (gimple_assign_lhs (ass)))
&& ((rhs_code = gimple_assign_rhs_code (ass)), true)
&& (rhs_code == TRUNC_DIV_EXPR
|| rhs_code == CEIL_DIV_EXPR
|| rhs_code == FLOOR_DIV_EXPR
|| rhs_code == ROUND_DIV_EXPR)
/* We cannot use expr_not_equal_to since we'd have to restrict
flow-sensitive info to whats known at the outer if. */
&& (TREE_CODE (gimple_assign_rhs2 (ass)) != INTEGER_CST
|| !integer_minus_onep (gimple_assign_rhs2 (ass))))
/* const calls don't match any of the above, yet they could
still have some side-effects - they could contain
gimple_could_trap_p statements, like floating point
@ -847,6 +863,19 @@ pass_tree_ifcombine::execute (function *fun)
/* Clear range info from all stmts in BB which is now executed
conditional on a always true/false condition. */
reset_flow_sensitive_info_in_bb (bb);
for (gimple_stmt_iterator gsi = gsi_start_bb (bb); !gsi_end_p (gsi);
gsi_next (&gsi))
{
gassign *ass = dyn_cast <gassign *> (gsi_stmt (gsi));
if (!ass)
continue;
tree lhs = gimple_assign_lhs (ass);
if ((INTEGRAL_TYPE_P (TREE_TYPE (lhs))
|| POINTER_TYPE_P (TREE_TYPE (lhs)))
&& arith_code_with_undefined_signed_overflow
(gimple_assign_rhs_code (ass)))
rewrite_to_defined_overflow (ass, true);
}
cfg_changed |= true;
}
}