[gcc r15-67] middle-end/13421 - -ftrapv vs. POINTER_DIFF_EXPR

[gcc r15-67] middle-end/13421 - -ftrapv vs. POINTER_DIFF_EXPR

[Richard Biener]

https://gcc.gnu.org/g:667c19de86b33648f5f4599f589a5e02adbb35cb

commit r15-67-g667c19de86b33648f5f4599f589a5e02adbb35cb
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Apr 16 14:05:35 2024 +0200

    middle-end/13421 - -ftrapv vs. POINTER_DIFF_EXPR
    
    Currently we expand POINTER_DIFF_EXPR using subv_optab when -ftrapv
    (but -fsanitize=undefined does nothing).  That's not consistent
    with the behavior of POINTER_PLUS_EXPR which never uses addv_optab
    with -ftrapv.  Both are because of the way we select whether to use
    the trapping or the non-trapping optab - we look at the result type
    of the expression and check
    
      trapv = INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_TRAPS (type);
    
    the bugreport correctly complains that -ftrapv affects pointer
    subtraction (there's no -ftrapv-pointer).  Now that we have
    POINTER_DIFF_EXPR we can honor that appropriately.
    
    The patch moves both POINTER_DIFF_EXPR and POINTER_PLUS_EXPR
    handling so they will never consider trapping (or saturating)
    optabs.
    
            PR middle-end/13421
            * optabs-tree.cc (optab_for_tree_code): Do not consider
            {add,sub}v or {us,ss}{add,sub} optabs for POINTER_DIFF_EXPR
            or POINTER_PLUS_EXPR.

Diff:
---
 gcc/optabs-tree.cc | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/gcc/optabs-tree.cc b/gcc/optabs-tree.cc
index e7bd0d10892..b69a5bc3676 100644
--- a/gcc/optabs-tree.cc
+++ b/gcc/optabs-tree.cc
@@ -135,6 +135,12 @@ optab_for_tree_code (enum tree_code code, const_tree type,
     case MIN_EXPR:
       return TYPE_UNSIGNED (type) ? umin_optab : smin_optab;
 
+    case POINTER_PLUS_EXPR:
+      return add_optab;
+
+    case POINTER_DIFF_EXPR:
+      return sub_optab;
+
     case REALIGN_LOAD_EXPR:
       return vec_realign_load_optab;
 
@@ -249,13 +255,11 @@ optab_for_tree_code (enum tree_code code, const_tree type,
   trapv = INTEGRAL_TYPE_P (type) && TYPE_OVERFLOW_TRAPS (type);
   switch (code)
     {
-    case POINTER_PLUS_EXPR:
     case PLUS_EXPR:
       if (TYPE_SATURATING (type))
 	return TYPE_UNSIGNED (type) ? usadd_optab : ssadd_optab;
       return trapv ? addv_optab : add_optab;
 
-    case POINTER_DIFF_EXPR:
     case MINUS_EXPR:
       if (TYPE_SATURATING (type))
 	return TYPE_UNSIGNED (type) ? ussub_optab : sssub_optab;