Re: [PATCH] c-family: ICE with -Wconversion and A ?: B [PR101030]

[Marek Polacek <polacek@redhat.com>]

On Tue, Mar 29, 2022 at 10:21:47PM -0400, Jason Merrill wrote:
> On 3/29/22 16:53, Marek Polacek wrote:
> > This patch fixes a crash in conversion_warning on a null expression.
> > It is null because the testcase uses the GNU A ?: B extension.  We
> > could also use op0 instead of op1 in this case, but it doesn't seem
> > to be necessary.
> 
> I wonder why we don't represent the extension as
> 
> SAVE_EXPR(A) ? SAVE_EXPR(A) : B
> 
> so we don't hit this sort of problem.  But the patch is OK.

The reason there are no SAVE_EXPRs is that we don't create them
in a template: cp_save_expr:

  /* There is no reason to create a SAVE_EXPR within a template; if
     needed, we can create the SAVE_EXPR when instantiating the
     template.  Furthermore, the middle-end cannot handle C++-specific
     tree codes.  */
  if (processing_template_decl)
    return expr;

and when instantiating we see the first expression is tree_invariant_p_1
aka constant, so no SAVE_EXPR gets created.

Patch pushed, thanks.

Marek