tree-object-size: Deterministic SSA generation [PR123351]

jakubjelinek · jakubjelinek · commit c6085ca0ed4c · 2026-01-06T08:36:20.000+01:00
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  &lt;jakub@redhat.com&gt;
	    Marco Falke  &lt;falke.marco@gmail.com&gt;

	PR tree-optimization/123351
	* tree-object-size.cc (object_sizes_set_temp): Separate calls to
	make_ssa_name to ensure deterministic execution order.
diff --git 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.  */
