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authorBjörn Gustavsson <[email protected]>2018-11-05 07:35:02 +0100
committerBjörn Gustavsson <[email protected]>2018-11-19 16:11:48 +0100
commit667e0e1213f69344a57c2eb0427d36cd240e16a5 (patch)
tree89fdafd3816a3651c36ae18151c2fd9b4d002849 /lib/compiler/src/beam_ssa_codegen.erl
parent0009fc378109f870472ded41d29c5d81febd5990 (diff)
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beam_ssa_codegen: Improve optimization of allocate instructions
There could be `allocate_zero` instructions where `allocate` would suffice or superfluous `init` instructions because all possible initializations of Y registers were not taken into account. While at it, also add some more comments.
Diffstat (limited to 'lib/compiler/src/beam_ssa_codegen.erl')
-rw-r--r--lib/compiler/src/beam_ssa_codegen.erl39
1 files changed, 35 insertions, 4 deletions
diff --git a/lib/compiler/src/beam_ssa_codegen.erl b/lib/compiler/src/beam_ssa_codegen.erl
index 3c14062d0b..d3facc5911 100644
--- a/lib/compiler/src/beam_ssa_codegen.erl
+++ b/lib/compiler/src/beam_ssa_codegen.erl
@@ -747,7 +747,16 @@ need_live_anno(Op) ->
end.
%%%
-%%% Add annotations for defined Y registers.
+%%% Add the following annotations for Y registers:
+%%%
+%%% def_yregs An ordset with variables that refer to live Y registers.
+%%% That is, Y registers that that have been killed
+%%% are not included. This annotation is added to all
+%%% instructions that require Y registers to be initialized.
+%%%
+%%% kill_yregs This annotation is added to call instructions. It is
+%%% an ordset containing variables referring to Y registers
+%%% that will no longer be used after the call instruction.
%%%
defined(Linear, #cg{regs=Regs}) ->
@@ -863,13 +872,35 @@ opt_allocate(Linear, #cg{regs=Regs}) ->
opt_allocate_1([{L,#cg_blk{is=[#cg_alloc{stack=Stk}=I0|Is]}=Blk0}|Bs]=Bs0, Regs)
when is_integer(Stk) ->
- Yregs = opt_alloc_def(Bs0, gb_sets:singleton(L), []),
- I = I0#cg_alloc{def_yregs=Yregs},
- [{L,Blk0#cg_blk{is=[I|Is]}}|opt_allocate_1(Bs, Regs)];
+ %% Collect the variables that are initialized by copy
+ %% instruction in this block.
+ case ordsets:from_list(opt_allocate_defs(Is, Regs)) of
+ Yregs when length(Yregs) =:= Stk ->
+ %% Those copy instructions are sufficient to fully
+ %% initialize the stack frame.
+ I = I0#cg_alloc{def_yregs=Yregs},
+ [{L,Blk0#cg_blk{is=[I|Is]}}|opt_allocate_1(Bs, Regs)];
+ Yregs0 ->
+ %% Determine a conservative approximation of the Y
+ %% registers that are guaranteed to be initialized by all
+ %% successors of this block, and to it add the variables
+ %% initialized by copy instructions in this block.
+ Yregs1 = opt_alloc_def(Bs0, gb_sets:singleton(L), []),
+ Yregs = ordsets:union(Yregs0, Yregs1),
+ I = I0#cg_alloc{def_yregs=Yregs},
+ [{L,Blk0#cg_blk{is=[I|Is]}}|opt_allocate_1(Bs, Regs)]
+ end;
opt_allocate_1([B|Bs], Regs) ->
[B|opt_allocate_1(Bs, Regs)];
opt_allocate_1([], _) -> [].
+opt_allocate_defs([#cg_set{op=copy,dst=Dst}|Is], Regs) ->
+ case is_yreg(Dst, Regs) of
+ true -> [Dst|opt_allocate_defs(Is, Regs)];
+ false -> []
+ end;
+opt_allocate_defs(_, _Regs) -> [].
+
opt_alloc_def([{L,#cg_blk{is=Is,last=Last}}|Bs], Ws0, Def0) ->
case gb_sets:is_member(L, Ws0) of
false ->