[gcc r14-4768] c++: small tweak for cp_fold_r

[gcc r14-4768] c++: small tweak for cp_fold_r

[Marek Polacek]

https://gcc.gnu.org/g:4d81962ba00ab74c4bc5fac685988f9cf778a9bb

commit r14-4768-g4d81962ba00ab74c4bc5fac685988f9cf778a9bb
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Oct 19 09:57:53 2023 -0400

    c++: small tweak for cp_fold_r
    
    This patch is an optimization tweak for cp_fold_r.  If we cp_fold_r the
    COND_EXPR's op0 first, we may be able to evaluate it to a constant if -O.
    cp_fold has:
    
    3143         if (callee && DECL_DECLARED_CONSTEXPR_P (callee)
    3144             && !flag_no_inline)
    ...
    3151             r = maybe_constant_value (x, /*decl=*/NULL_TREE,
    
    flag_no_inline is 1 for -O0:
    
    1124   if (opts->x_optimize == 0)
    1125     {
    1126       /* Inlining does not work if not optimizing,
    1127          so force it not to be done.  */
    1128       opts->x_warn_inline = 0;
    1129       opts->x_flag_no_inline = 1;
    1130     }
    
    but otherwise it's 0 and cp_fold will maybe_constant_value calls to
    constexpr functions.  And if it doesn't, then folding the COND_EXPR
    will keep both arms, and we can avoid calling maybe_constant_value.
    
    gcc/cp/ChangeLog:
    
            * cp-gimplify.cc (cp_fold_r): Don't call maybe_constant_value.

Diff:
---
 gcc/cp/cp-gimplify.cc | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index a282c3930a37..33e9411f10c6 100644
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -1152,13 +1152,12 @@ cp_fold_r (tree *stmt_p, int *walk_subtrees, void *data_)
 	  auto then_fn = cp_fold_r, else_fn = cp_fold_r;
 	  /* See if we can figure out if either of the branches is dead.  If it
 	     is, we don't need to do everything that cp_fold_r does.  */
-	  tree cond = maybe_constant_value (TREE_OPERAND (stmt, 0));
-	  if (integer_zerop (cond))
+	  cp_walk_tree (&TREE_OPERAND (stmt, 0), cp_fold_r, data, nullptr);
+	  if (integer_zerop (TREE_OPERAND (stmt, 0)))
 	    then_fn = cp_fold_immediate_r;
-	  else if (TREE_CODE (cond) == INTEGER_CST)
+	  else if (integer_nonzerop (TREE_OPERAND (stmt, 0)))
 	    else_fn = cp_fold_immediate_r;
 
-	  cp_walk_tree (&TREE_OPERAND (stmt, 0), cp_fold_r, data, nullptr);
 	  if (TREE_OPERAND (stmt, 1))
 	    cp_walk_tree (&TREE_OPERAND (stmt, 1), then_fn, data,
 			  nullptr);