on 2022/6/15 14:20, Kewen.Lin wrote: > Hi Honza, > > Thanks for the comments! Some replies are inlined below. > > on 2022/6/14 19:37, Jan Hubicka wrote: >>> Hi, >>> >>> Function optimize_function_for_size_p returns OPTIMIZE_SIZE_NO >>> if func->decl is not null but no cgraph node is available for it. >>> As PR105818 shows, this could give unexpected result. For the >>> case in PR105818, when parsing bar decl in function foo, the cfun >>> is a function structure for foo, for which there is none cgraph >>> node, so it returns OPTIMIZE_SIZE_NO. But it's incorrect since >>> the context is to optimize for size, the flag optimize_size is >>> true. >>> >>> The patch is to make optimize_function_for_size_p to check >>> optimize_size as what it does when func->decl is unavailable. >>> >>> One regression failure got exposed on aarch64-linux-gnu: >>> >>> PASS->FAIL: gcc.dg/guality/pr54693-2.c -Os \ >>> -DPREVENT_OPTIMIZATION line 21 x == 10 - i >>> >>> The difference comes from the macro LOGICAL_OP_NON_SHORT_CIRCUIT >>> used in function fold_range_test during c parsing, it uses >>> optimize_function_for_speed_p which is equal to the invertion >>> of optimize_function_for_size_p. At that time cfun->decl is valid >>> but no cgraph node for it, w/o this patch function >>> optimize_function_for_speed_p returns true eventually, while it >>> returns false with this patch. Since the command line option -Os >>> is specified, there is no reason to interpret it as "for speed". >>> I think this failure is expected and adjust the test case >>> accordingly. >>> >>> Is it ok for trunk? >>> >>> BR, >>> Kewen >>> ----- >>> >>> PR target/105818 >>> >>> gcc/ChangeLog: >>> >>> * predict.cc (optimize_function_for_size_p): Check optimize_size when >>> func->decl is valid but its cgraph node is unavailable. >>> >>> gcc/testsuite/ChangeLog: >>> >>> * gcc.target/powerpc/pr105818.c: New test. >>> * gcc.dg/guality/pr54693-2.c: Adjust for aarch64. >>> --- >>> gcc/predict.cc | 2 +- >>> gcc/testsuite/gcc.dg/guality/pr54693-2.c | 2 +- >>> gcc/testsuite/gcc.target/powerpc/pr105818.c | 9 +++++++++ >>> 3 files changed, 11 insertions(+), 2 deletions(-) >>> create mode 100644 gcc/testsuite/gcc.target/powerpc/pr105818.c >>> >>> diff --git a/gcc/predict.cc b/gcc/predict.cc >>> index 5734e4c8516..6c60a973236 100644 >>> --- a/gcc/predict.cc >>> +++ b/gcc/predict.cc >>> @@ -268,7 +268,7 @@ optimize_function_for_size_p (struct function *fun) >>> cgraph_node *n = cgraph_node::get (fun->decl); >>> if (n) >>> return n->optimize_for_size_p (); >>> - return OPTIMIZE_SIZE_NO; >>> + return optimize_size ? OPTIMIZE_SIZE_MAX : OPTIMIZE_SIZE_NO; >> >> We could also do (opt_for_fn (cfun->decl, optimize_size) that is >> probably better since one can change optimize_size with optimization >> attribute. > > Good point, agree! > >> However I think in most cases we check for optimize_size early I think >> we are doing something wrong, since at that time htere is no profile >> available. Why exactly PR105818 hits the flag change issue? > > For PR105818, the reason why the flag changs is that: > > Firstly, the inconsistent flag is OPTION_MASK_SAVE_TOC_INDIRECT bit > of rs6000_isa_flags_explicit, it's set as below: > > /* If we can shrink-wrap the TOC register save separately, then use > -msave-toc-indirect unless explicitly disabled. */ > if ((rs6000_isa_flags_explicit & OPTION_MASK_SAVE_TOC_INDIRECT) == 0 > && flag_shrink_wrap_separate > && optimize_function_for_speed_p (cfun)) > rs6000_isa_flags |= OPTION_MASK_SAVE_TOC_INDIRECT; > > Initially, rs6000 initialize target_option_default_node with > OPTION_MASK_SAVE_TOC_INDIRECT unset, at that time cfun is NULL > and optimize_size is true. > > Later, when c parser handling function foo, it builds target > option node as target_option_default_node in function > handle_optimize_attribute, it does global option saving and > verifying there as well, at that time the cfun is NULL, no > issue is found. And function store_parm_decls allocates > struct_function for foo then, cfun becomes function struct > for foo, when c parser continues to handle the decl bar in > foo, function handle_optimize_attribute works as before, > tries to restore the target options at the end, it calls > targetm.target_option.restore (rs6000_function_specific_restore) > which calls function rs6000_option_override_internal again, > at this time the cfun is not NULL while there is no cgraph > node for its decl, optimize_function_for_speed_p returns true > and gets the OPTION_MASK_SAVE_TOC_INDIRECT bit of flag > rs6000_isa_flags set unexpectedly. It becomes inconsistent > as the one saved previously. > > IMHO, both contexts of global and function decl foo here hold > optimize_size, function optimize_function_for_speed_p should > not return true anyway. > > btw, the aarch64 failed case also gets the unexpected > result for optimize_function_for_speed_p during c parsing > (fold_range_test <- ... <- c_parser_condition). > > IIUC, in parsing time we don't have the profile information > available. >
Hi Honza, Does the above explanation sound reasonable to you? BR, Kewen
