inline_small_functions speedup

inline_small_functions speedup

After inlining A into B, inline_small_functions updates the information
for (most) callees and callers of the new B:

	  update_callee_keys (&edge_heap, where, updated_nodes);
      [...]
      /* Our profitability metric can depend on local properties
	 such as number of inlinable calls and size of the function body.
	 After inlining these properties might change for the function we
	 inlined into (since it's body size changed) and for the functions
	 called by function we inlined (since number of it inlinable callers
	 might change).  */
      update_caller_keys (&edge_heap, where, updated_nodes, NULL);

These functions in turn call can_inline_edge_p for most of the associated
edges:

	    if (can_inline_edge_p (edge, false)
		&& want_inline_small_function_p (edge, false))
	      update_edge_key (heap, edge);

can_inline_edge_p indirectly calls estimate_calls_size_and_time
on the caller node, which seems to recursively process all callee
edges rooted at the node.  It looks from this like the algorithm
can be at least quadratic in the worst case.

Maybe there's something we can do to make can_inline_edge_p cheaper, but
since neither of these two calls is responsible for reporting an inline
failure reason, it seems cheaper to test want_inline_small_function_p
first, so that we don't calculate an estimate for something that we
already know isn't a "small function".  I think the only change
needed to make that work is to check for CIF_FINAL_ERROR in
want_inline_small_function_p; at the moment we rely on can_inline_edge_p
to make that check.

This cuts the time to build optabs.ii by over 4% with an
--enable-checking=release compiler on x86_64-linux-gnu.  I've seen more
dramatic wins on aarch64-linux-gnu due to the NUM_POLY_INT_COEFFS==2
thing.  The patch doesn't affect the output code.

2018-01-13  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* ipa-inline.c (want_inline_small_function_p): Return false if
	inlining has already failed with CIF_FINAL_ERROR.
	(update_caller_keys): Call want_inline_small_function_p before
	can_inline_edge_p.
	(update_callee_keys): Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@256658 138bc75d-0d04-0410-961f-82ee72b054a4