[ast-optimizer-branch] PATCH to &&, ++ and return

[Jason Merrill]

The bottom ChangeLog bits are infrastructure for the upper three, which are
independent of one another, but I'm checking them in together because I'm
lazy.

get_initialized_tmp_var creates a new initialized temp, so callers don't
  have to deal with building up, simplifying and adding a MODIFY_EXPR.

simplify_expr_common now takes a NULL post_p argument; in this case, if the
  expression being simplified has post-effects, the result will be copied
  to a temp and the post-effects emitted before returning.  This is used in
  simplify_return_stmt here, and will be used in the loop nodes in a later
  patch.

I've changed simplify_return_stmt to accept an RHS, while the grammar says
it should only accept a VAL.  The reason for this is to avoid an extra temp
on code like

  struct A f ();
  struct A g ()
  {
    return f ();
  }

Here, if we require a VAL, we need to copy the returned struct into our
stack frame before returning it.  This can be slow, depending on the size
of A.  And a return statement is already represented with a MODIFY_EXPR,
anyway...

I've fixed simplify_self_mod_expr so that an expression like (*f())++ only
calls f once.  This fixes gcc.dg/20020426-2.c.

I've fixed simplify_boolean_expr so that the temp used to keep track of the
current state has the appropriate boolean type (int, in C); previously it
would get the type of the && expression, which could be an arbitrary type.
In gcc.c-torture/compile/980706-1.c there is a && expression which ends up
having long long type.  I've also reduced the number of comparisons we
build; we know that T is a boolean value, we don't need to keep comparing
it to zero.

Booted and tested i686-pc-linux-gnu.  Also fixes gcc.dg/uninit-A.c, though
that may be transient.

2002-06-10  Jason Merrill  <jason@redhat.com>

	* c-simplify.c (simplify_boolean_expr): Avoid redundant tests.
	Give the temp the appropriate type for a boolean value, and
	reconvert at the end.

	* c-simplify.c (simplify_self_mod_expr): Don't duplicate side-effects.

	* c-simplify.c (simplify_return_stmt): Accept a SIMPLE rhs.
	Just hand off to simplify_expr.

	* c-simplify.c (get_initialized_tmp_var): New fn.
	(simplify_expr_common): Use it.  Handle post-effects internally if
	POST_P is NULL.
	(is_simple_tmp_var): Rename from simple_tmp_var_p.
	* tree-simple.h: Adjust.

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