[gcc r16-6110] middle-end: Fix spurious -Walloc-size-larger-than warning during LTO [PR106409]

[Lewis Hyatt]

https://gcc.gnu.org/g:8e23a9982fa4b885a27608825cbe326d61f20498

commit r16-6110-g8e23a9982fa4b885a27608825cbe326d61f20498
Author: Lewis Hyatt <lhyatt@gmail.com>
Date:   Sun Dec 14 09:51:12 2025 -0500

    middle-end: Fix spurious -Walloc-size-larger-than warning during LTO [PR106409]
    
    The implementation of -Walloc-size-larger-than has logic to avoid issuing
    the warning for ::operator new[] calls emitted by the C++ front end, which
    otherwise produce known false positives.  The logic for suppressing the
    warning only activates in the C++ front end, and so it does not prevent the
    LTO front end from issuing the warning.  Fix by applying the logic in all
    cases.
    
    gcc/ChangeLog:
    
            PR tree-optimization/106409
            * gimple-ssa-warn-access.cc (maybe_warn_alloc_args_overflow): Adjust
            comment for clarity, and augment check to work in LTO as well.
    
    gcc/testsuite/ChangeLog:
    
            PR tree-optimization/106409
            * g++.dg/lto/pr106409_0.C: New test.

Diff:
---
 gcc/gimple-ssa-warn-access.cc         | 10 +++++-----
 gcc/testsuite/g++.dg/lto/pr106409_0.C | 23 +++++++++++++++++++++++
 2 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index d12f797f36b3..0625a36ca35a 100644
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -2334,14 +2334,14 @@ maybe_warn_alloc_args_overflow (gimple *stmt, const tree args[2],
 	    }
 	  else if (tree_int_cst_lt (maxobjsize, args[i]))
 	    {
-	      /* G++ emits calls to ::operator new[](SIZE_MAX) in C++98
-		 mode and with -fno-exceptions as a way to indicate array
-		 size overflow.  There's no good way to detect C++98 here
-		 so avoid diagnosing these calls for all C++ modes.  */
+	      /* G++ emits calls to ::operator new[](SIZE_MAX) in C++98 mode or
+		 with -fno-exceptions as a way to indicate array size overflow.
+		 Avoid diagnosing these calls.  Additionally, see e.g. PR99934,
+		 G++ also potentially generates such calls in C++11 and later as
+		 well, so suppress the diagnostic in all C++ modes.  */
 	      if (i == 0
 		  && fn
 		  && !args[1]
-		  && lang_GNU_CXX ()
 		  && DECL_IS_OPERATOR_NEW_P (fn)
 		  && integer_all_onesp (args[i]))
 		continue;
diff --git a/gcc/testsuite/g++.dg/lto/pr106409_0.C b/gcc/testsuite/g++.dg/lto/pr106409_0.C
new file mode 100644
index 000000000000..464d13a79479
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lto/pr106409_0.C
@@ -0,0 +1,23 @@
+/* PR tree-optimization/106409 */
+/* { dg-lto-do link } */
+/* { dg-lto-options { { -flto -W -Wall -O2 -fno-exceptions } { -flto -W -Wall -O2 -std=c++98 } { -flto -W -Wall -O2 -std=gnu++20 } } } */
+struct bb
+{
+  int t;
+  int t1;
+  int t2;
+  int t3;
+};
+
+[[gnu::noipa]]
+void *f(unsigned long paramCount)
+{
+    if (paramCount == 0)
+      return 0;
+    return new bb[paramCount]();
+}
+
+int main(void)
+{
+  f(100);
+}