gimple UIDs, LTO and -fanalyzer [PR98599]

gimple UIDs, LTO and -fanalyzer [PR98599]

gimple.h has this comment for gimple's uid field:

  /* UID of this statement.  This is used by passes that want to
     assign IDs to statements.  It must be assigned and used by each
     pass.  By default it should be assumed to contain garbage.  */
  unsigned uid;

and gimple_set_uid has:

   Please note that this UID property is supposed to be undefined at
   pass boundaries.  This means that a given pass should not assume it
   contains any useful value when the pass starts and thus can set it
   to any value it sees fit.

which suggests that any pass can use the uid field as an arbitrary
scratch space.

PR analyzer/98599 reports a case where this error occurs in LTO mode:
  fatal error: Cgraph edge statement index out of range
on certain inputs with -fanalyzer.

The error occurs in the LTRANS phase after -fanalyzer runs in the
WPA phase.  The analyzer pass writes to the uid fields of all stmts.

The error occurs when LTRANS is streaming callgraph edges back in.
The LTO format uses stmt uids to associate call stmts with callgraph
edges between WPA and LTRANS.
For example, in lto-cgraph.c, lto_output_edge writes out the
gimple_uid, and input_edge reads it back in.

lto_prepare_function_for_streaming has code to renumber the stmt UIDs
when the code is streamed back out, but for some reason this isn't
called for clones:
    307	  /* Do body modifications needed for streaming before we fork out
    308	     worker processes.  */
    309	  FOR_EACH_FUNCTION_WITH_GIMPLE_BODY (node)
    310	    if (!node->clone_of && gimple_has_body_p (node->decl))
    311	      lto_prepare_function_for_streaming (node);

Hence the combination of -fanalyzer and -flto will fail in LTRANS's
stream-in if any function clones are encountered.

It's not fully clear to me why this isn't done for clones, and what the
correct fix should be to allow arbitrary changes to uids within WPA
passes.

In the meantime, this patch works around the issue by updating the
analyzer to save and restore the UIDs, fixing the error.

gcc/analyzer/ChangeLog:
	PR analyzer/98599
	* supergraph.cc (saved_uids::make_uid_unique): New.
	(saved_uids::restore_uids): New.
	(supergraph::supergraph): Replace assignments to stmt->uid with
	calls to m_stmt_uids.make_uid_unique.
	(supergraph::~supergraph): New.
	* supergraph.h (class saved_uids): New.
	(supergraph::~supergraph): New decl.
	(supergraph::m_stmt_uids): New field.

gcc/testsuite/ChangeLog:
	PR analyzer/98599
	* gcc.dg/analyzer/pr98599-a.c: New test.
	* gcc.dg/analyzer/pr98599-b.c: New test.