[gcc r13-131] rewrite undefined overflow to defined in ifcombine

[gcc r13-131] rewrite undefined overflow to defined in ifcombine

[Richard Biener]

https://gcc.gnu.org/g:c2a0d2e6f636c6ad7da44256b6bea7470d895100

commit r13-131-gc2a0d2e6f636c6ad7da44256b6bea7470d895100
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Apr 4 11:29:14 2022 +0200

    rewrite undefined overflow to defined in ifcombine
    
    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.

Diff:
---
 gcc/tree-ssa-ifcombine.cc | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/gcc/tree-ssa-ifcombine.cc b/gcc/tree-ssa-ifcombine.cc
index 3a4ab694b71..cb86cc1ea5f 100644
--- a/gcc/tree-ssa-ifcombine.cc
+++ b/gcc/tree-ssa-ifcombine.cc
@@ -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;
 	  }
     }