Re: Tree sharing issues...

[law at redhat dot com]

In message <20031119230806.GU11681@kam.mff.cuni.cz>, Jan Hubicka writes:
 >> In message <20031119225619.GR11681@kam.mff.cuni.cz>, Jan Hubicka writes:
 >>  >> In message <20031119224619.GP11681@kam.mff.cuni.cz>, Jan Hubicka writes
 >:
 >>  >>  >>  >OK, I will extend my sharing test by is_gimple_min_invariant.  Do
 >es t
 >>  >hat
 >>  >>  >>  >look right?
 >>  >>  >> is_gimple_min_invariant (blah) && ! IS_EMPTY_STMT (blah) since I
 >>  >>  >> believe the empty statement is (void) 0, but is not shared.
 >>  >>  >> 
 >>  >>  >> Ugh.
 >>  >>  >OK, another positive:
 >>  >>  >../../gcc/caller-save.c:370: error: Wrong sharing of tree nodes
 >>  >>  >#   hard_regs_to_save_6 = VDEF <hard_regs_to_save_624>;
 >>  >>  >hard_regs_to_save[1] = T.329_1370;
 >>  >>  >
 >>  >>  >hard_regs_to_save[1];
 >>  >>  >
 >>  >>  >../../gcc/caller-save.c:370: error: Wrong sharing of tree nodes
 >>  >>  >#   hard_regs_to_save_143 = VDEF <hard_regs_to_save_81>;
 >>  >>  >hard_regs_to_save[1] = T.339_1393;
 >>  >>  >
 >>  >>  >hard_regs_to_save[1];
 >>  >>  >
 >>  >>  >../../gcc/caller-save.c:370: error: Wrong sharing of tree nodes
 >>  >>  >#   hard_regs_to_save_623 = VDEF <hard_regs_to_save_488>;
 >>  >>  >hard_regs_to_save[1] = T.349_1416;
 >>  >>  >
 >>  >>  >hard_regs_to_save[1];
 >>  >>  >
 >>  >>  >../../gcc/caller-save.c:370: error: Wrong sharing of tree nodes
 >>  >>  >#   hard_regs_to_save_80 = VDEF <hard_regs_to_save_5>;
 >>  >>  >hard_regs_to_save[1] = T.357_1437;
 >>  >>  >
 >>  >>  >hard_regs_to_save[1];
 >>  >>  >
 >>  >>  >
 >>  >>  >This looks wrong.  Seems to happen during jump threading...
 >>  >> I'm not sure why we wouldn't be sharing that node
 >>  >> (hard_regs_to_save[1]).
 >>  >> 
 >>  >> Diego?
 >>  >I can add it into my definition of shareable nodes, if you tell me how
 >>  >to recognize these.
 >> 
 >>  TREE_ADDRESSABLE (var)
 >>   || decl_function_context (var) != current_function_decl
 >>   || may_aliases (var)
 >> 
 >> Or something close to that.
 >I am already allowing sharing of all DECL_P nodes.  The node above is
 >ARRAY_REF with constant operand, isn't it?  So I need some kind of test
 >"if array_ref is having all arguments constant, then it can be shared"
 >or am I wrong?
Well, you also need to allow sharing of certain constants, SSA_NAME nodes
and probably other stuff.

Fundamentally trees haven't had well defined sharing rules, so you're going
to largely have to "figure things out and document them".


Jeff