Re: Do not emit unnecessary NOPs at -O0

[Jeff Law <law at redhat dot com>]

On 06/21/2018 11:04 AM, Eric Botcazou wrote:
> When code is compiled at -O0, the RTL middle-end makes sure that location 
> information is preserved as much as possible by generating NOPs with the 
> location information (goto_locus) present on edges in the CFG, if it thinks 
> that these edges are the only place where a particular location is mentioned.
> 
> The attached patch prevents this from happening in a couple of cases:
>  1. if the function has the DECL_IGNORED_P flag set,
>  2. if the NOP is emitted by merge_blocks and the 2nd block is a forwarder 
> block whose outgoing edge has no location, because in this case the location 
> of the to-be-elided edge is copied onto the aforementioned outgoing edge.
> 
> Tested (GCC and GDB) on x86-64/Linux, applied on the mainline.
> 
> 
> 2018-06-21  Eric Botcazou  <ebotcazou@adacore.com>
> 
> 	* cfgrtl.c (fixup_reorder_chain): Do not emit NOPs in DECL_IGNORED_P
>  	functions.
> 	(rtl_merge_blocks): Likewise.  Do not emit a NOP if the location of the
> 	edge can be forwarded.
> 	(cfg_layout_merge_blocks): Likewise.
> 
OK
Jeff