RE: [RFC] ipa: Adjust references to identify read-only globals

[JiangNing OS <jiangning@os.amperecomputing.com>]

> -----Original Message-----
> From: Gcc-patches <gcc-patches-
> bounces+jiangning=os.amperecomputing.com@gcc.gnu.org> On Behalf Of
> Martin Jambor
> Sent: Wednesday, June 30, 2021 4:19 AM
> To: GCC Patches <gcc-patches@gcc.gnu.org>
> Cc: Jan Hubicka <hubicka@ucw.cz>
> Subject: [RFC] ipa: Adjust references to identify read-only globals
> 
> Hi,
> 
> this patch has been motivated by SPEC 2017's 544.nab_r in which there is a
> static variable which is never written to and so zero throughout the run-time
> of the benchmark.  However, it is passed by reference to a function in which
> it is read and (after some multiplications) passed into __builtin_exp which in
> turn unnecessarily consumes almost 10% of the total benchmark run-time.

I do see ~8.5% runtime reduction on aarch64.

> The situation is illustrated by the added testcase remref-3.c.
> 
> The patch adds a flag to ipa-prop descriptor of each parameter to mark such
> parameters.  IPA-CP and inling then take the effort to remove IPA_REF_ADDR
> references in the caller and only add IPA_REF_LOAD reference to the
> clone/overall inlined function.  This is sufficient for subsequent symbol table
> analysis code to identify the read-only variable as such and optimize the code.
> 
> I plan to compile a number of packages with the patch to test it some more
> and get a bit better idea of its impact.  But it has passed bootstrap,
> LTObootstrap and testing on x86_64-linux and i686-linux and so unless I find
> any problem, I would like to commit it at some point next month without any
> major changes, so I'd be grateful for any feedback even now.

I see 3 cases in SPEC2017 failed to compile on aarch64, i.e. 521.wrf_r, 527.cam4_r, 554.roms_r. For example,

pre_step3d.fppized.f90:1260:35: internal compiler error: Segmentation fault
 1260 |       CALL wclock_on (ng, iNLM, 22)
      |                                   ^
0x1645c6b internal_error(char const*, ...)
	???:0
0xe1f4f4 place_block_symbol(rtx_def*)
	???:0
0x84ab33 use_anchored_address(rtx_def*)
	???:0
0x868203 expand_expr_real_1(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool)
	???:0
0x868793 expand_expr_real_1(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool)
	???:0
0x75b593 expand_call(tree_node*, rtx_def*, int)
	???:0
0x86a09f expand_expr_real_1(tree_node*, rtx_def*, machine_mode, expand_modifier, rtx_def**, bool)
	???:0
Please submit a full bug report

Thanks,
-Jiangning