Re: [PATCH 2/3] Implement CALL_EXPR_MUST_TAIL_CALL

[Jeff Law]

On 05/17/2016 04:01 PM, David Malcolm wrote:
This patch implements support for marking CALL_EXPRs
as being mandatory for tail-call-optimization. expand_call
tries harder to perform the optimization on such CALL_EXPRs,
and issues an error if it fails.
Currently this flag isn't accessible from any frontend,
so the patch uses a plugin for testing the functionality.

Successfully bootstrapped&regrtested on x86_64-pc-linux-gnu;
adds 8 PASS results to gcc.sum.

OK for trunk?

gcc/ChangeLog:
        * calls.c (maybe_complain_about_tail_call): New function.
        (initialize_argument_information): Call
        maybe_complain_about_tail_call when clearing *may_tailcall.
        (can_implement_as_sibling_call_p): Call
        maybe_complain_about_tail_call when returning false.
        (expand_call): Read CALL_EXPR_MUST_TAIL_CALL and, if set,
        ensure try_tail_call is set.  Call maybe_complain_about_tail_call
        if tail-call optimization fails.
        * cfgexpand.c (expand_call_stmt): Initialize
        CALL_EXPR_MUST_TAIL_CALL from gimple_call_must_tail_p.
        * gimple-pretty-print.c (dump_gimple_call): Dump
        gimple_call_must_tail_p.
        * gimple.c (gimple_build_call_from_tree): Call
        gimple_call_set_must_tail with the value of
        CALL_EXPR_MUST_TAIL_CALL.
        * gimple.h (enum gf_mask): Add GF_CALL_MUST_TAIL_CALL.
        (gimple_call_set_must_tail): New function.
        (gimple_call_must_tail_p): New function.
        * print-tree.c (print_node): Update printing of TREE_STATIC
        to reflect its use for CALL_EXPR_MUST_TAIL_CALL.
        * tree-core.h (struct tree_base): Add MUST_TAIL_CALL to the
        trailing comment listing applicable flags.
        * tree.h (CALL_EXPR_MUST_TAIL_CALL): New macro.
It's actually simpler than it looks -- most of the changes are just 
getting better diagnostics when tail call fails, which I wholeheartedly 
support.

OK for the trunk.


Thanks,
Jeff