[gcc r16-9314] testsuite: skip test for targets that can deref null [PR126261]

[Torbjorn Svensson]

https://gcc.gnu.org/g:307954e9c03aba314d6050d36edc056887df9a5d

commit r16-9314-g307954e9c03aba314d6050d36edc056887df9a5d
Author: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
Date:   Tue Jul 14 16:38:10 2026 +0200

    testsuite: skip test for targets that can deref null [PR126261]
    
    As arm-none-eabi targets might have readable memory at address 0,
    g++.dg/torture/pr101373.C test will "work" on some targets, while others
    might tigger a fault. To avoid the ambiguity, lets skip the test if
    target allows null to be dereferenced.
    
            PR testsuite/126261
    
    gcc/ChangeLog:
    
            * doc/sourcebuild.texi (can_deref_null): Document.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/torture/pr101373.C: Use effective-target can_deref_null.
            * lib/target-supports.exp (check_effective_target_can_deref_null):
            New proc.
    
    Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
    (cherry picked from commit 2e26607f7f14bd32ea8082ee626f207d6a9f87a0)

Diff:
---
 gcc/doc/sourcebuild.texi                |  4 ++++
 gcc/testsuite/g++.dg/torture/pr101373.C |  1 +
 gcc/testsuite/lib/target-supports.exp   | 20 ++++++++++++++++++++
 3 files changed, 25 insertions(+)

diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index cea1fd3872f5..069fd3892a7d 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -2723,6 +2723,10 @@ Target supports the execution of @code{amx-tf32} instructions.
 @item amx_fp8
 Target supports the execution of @code{amx-fp8} instructions.
 
+@item can_deref_null
+Target runtime permits dereferencing a null pointer without trapping, for
+example because address zero is mapped and readable.
+
 @item cell_hw
 Test system can execute AltiVec and Cell PPU instructions.
 
diff --git a/gcc/testsuite/g++.dg/torture/pr101373.C b/gcc/testsuite/g++.dg/torture/pr101373.C
index f8c809739e2d..45f1e455eec3 100644
--- a/gcc/testsuite/g++.dg/torture/pr101373.C
+++ b/gcc/testsuite/g++.dg/torture/pr101373.C
@@ -1,5 +1,6 @@
 // { dg-do run }
 // { dg-xfail-run-if "PR100409" { *-*-* } }
+// { dg-skip-if "PR126261" { can_deref_null } }
 
 int __attribute__((const,noipa)) foo (int j)
 {
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 4037ffe9319b..773ea3af570d 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -15027,3 +15027,23 @@ proc check_effective_target_memtag_exec {} {
       }
     return 1;
 }
+
+# Return 1 if the target runtime can deref null, 0 otherwise.
+# Cache the result.
+
+proc check_effective_target_can_deref_null { } {
+    return [check_runtime can_deref_null {
+	char __attribute__((noipa))
+	read_mem (volatile char *p)
+	{
+	  return *p;
+	}
+
+	int
+	main ()
+	{
+	  read_mem (0);
+	  return 0;
+	}
+      } "-O0 -fno-delete-null-pointer-checks -Wno-null-dereference"]
+}