[gcc r16-6516] tree-object-size: Deterministic SSA generation [PR123351]

[Jakub Jelinek]

https://gcc.gnu.org/g:c6085ca0ed4cef3bcf4eb382cb71e44219c10f6e

commit r16-6516-gc6085ca0ed4cef3bcf4eb382cb71e44219c10f6e
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jan 6 08:36:20 2026 +0100

    tree-object-size: Deterministic SSA generation [PR123351]
    
    The order of evaluation of function arguments is unspecified in C++.
    The function object_sizes_set_temp called object_sizes_set with two
    calls to make_ssa_name() as arguments.  Since make_ssa_name() has the
    side effect of incrementing the global SSA version counter, different
    architectures of the same compiler evaluated these calls in different
    orders.
    
    This resulted in non-deterministic SSA version numbering between
    x86_64 and aarch64 hosts during cross-compilation, leading to
    divergent object files.
    
    Sequencing the calls into separate statements ensures deterministic
    evaluation order.
    
    2026-01-06  Jakub Jelinek  <jakub@redhat.com>
                Marco Falke  <falke.marco@gmail.com>
    
            PR tree-optimization/123351
            * tree-object-size.cc (object_sizes_set_temp): Separate calls to
            make_ssa_name to ensure deterministic execution order.

Diff:
---
 gcc/tree-object-size.cc | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/gcc/tree-object-size.cc b/gcc/tree-object-size.cc
index 01a59b8434ca..908647b84016 100644
--- a/gcc/tree-object-size.cc
+++ b/gcc/tree-object-size.cc
@@ -322,9 +322,11 @@ object_sizes_set_temp (struct object_size_info *osi, unsigned varno)
   tree val = object_sizes_get (osi, varno);
 
   if (size_initval_p (val, osi->object_size_type))
-    object_sizes_set (osi, varno,
-		      make_ssa_name (sizetype),
-		      make_ssa_name (sizetype));
+    {
+      val = make_ssa_name (sizetype);
+      tree wholeval = make_ssa_name (sizetype);
+      object_sizes_set (osi, varno, val, wholeval);
+    }
 }
 
 /* Initialize OFFSET_LIMIT variable.  */