tree-assume: Fix UB in assume_query [PR118605]

The assume_query constructor does
assume_query::assume_query (function *f, bitmap p) : m_parm_list (p),
                                                     m_func (f)
where m_parm_list is bitmap &.  This is compile time UB, because
as soon as the constructor returns, m_parm_list reference is still
bound to the parameter of the constructor which is no longer in scope.

Now, one possible fix would be change the ctor argument to be bitmap &,
but that doesn't really work because in the only user of that class
we have
      auto_bitmap decls;
...
      assume_query query (fun, decls);
and auto_bitmap just has
  operator bitmap () { return &m_bits; }
Could be perhaps const bitmap &, but why?  bitmap is a pointer:
typedef class bitmap_head *bitmap;
and the EXECUTE_IF_SET_IN_BITMAP macros don't really change that point,
they just inspect what is inside of that bitmap_head the pointer points
to.

So, the simplest I think is avoid references (which cause even worse
code as it has to be dereferenced twice rather than once).

2025-01-23  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/118605
	* tree-assume.cc (assume_query::m_parm_list): Change type
	from bitmap & to bitmap.

(cherry picked from commit 27a05f8d11798889ecfb610db9bde781c3d218f7)

diff --git a/gcc/tree-assume.cc b/gcc/tree-assume.cc
index 10c1343492c04aa3d2b6e62026f1264a606d1310..58b800fbe6c1d3d821aff1eb8c21cc7991ae712c 100644 (file)
--- a/gcc/tree-assume.cc
+++ b/gcc/tree-assume.cc
@@ -98,7 +98,7 @@ protected:
   ssa_lazy_cache m_path;   // Values found on path
   ssa_lazy_cache m_parms;  // Cumulative parameter value calculated
   gimple_ranger *m_ranger;
-  bitmap &m_parm_list;    // Parameter ssa-names list.
+  bitmap m_parm_list;     // Parameter ssa-names list.
   function *m_func;
 };