[gcc r13-6435] [c++] suppress redundant null-addr warn in pfn from pmfn

[Alexandre Oliva <aoliva@gcc.gnu.org>]

https://gcc.gnu.org/g:2e8686cb51896e0f89b353ae599c2c1ac5b960d6

commit r13-6435-g2e8686cb51896e0f89b353ae599c2c1ac5b960d6
Author: Alexandre Oliva <oliva@adacore.com>
Date:   Fri Mar 3 01:46:56 2023 -0300

    [c++] suppress redundant null-addr warn in pfn from pmfn
    
    When TARGET_PTRMEMFUNC_VBIT_LOCATION == ptrmemfunc_vbit_in_delta, when
    we warn about comparing a pointer-to-member-function with NULL, we
    also warn about comparing the pointer-to-function extracted from it
    with NULL, which is redundant.  Suppress the redundant warning.
    
    
    for  gcc/cp/ChangeLog
    
            * typeck.cc (cp_build_binary_op): Suppress redundant warning
            for pfn null test in pmfn test with vbit-in-delta.

Diff:
---
 gcc/cp/typeck.cc | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 4afb5e4f0d4..d5a3e501d8e 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -5780,11 +5780,18 @@ cp_build_binary_op (const op_location_t &location,
 
 	      pfn0 = pfn_from_ptrmemfunc (op0);
 	      delta0 = delta_from_ptrmemfunc (op0);
-	      e1 = cp_build_binary_op (location,
-				       EQ_EXPR,
-	  			       pfn0,
-				       build_zero_cst (TREE_TYPE (pfn0)),
-				       complain);
+	      {
+		/* If we will warn below about a null-address compare
+		   involving the orig_op0 ptrmemfunc, we'd likely also
+		   warn about the pfn0's null-address compare, and
+		   that would be redundant, so suppress it.  */
+		warning_sentinel ws (warn_address);
+		e1 = cp_build_binary_op (location,
+					 EQ_EXPR,
+					 pfn0,
+					 build_zero_cst (TREE_TYPE (pfn0)),
+					 complain);
+	      }
 	      e2 = cp_build_binary_op (location,
 				       BIT_AND_EXPR,
 				       delta0,