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authorMagnus Lång <[email protected]>2016-09-24 09:37:46 +0200
committerMagnus Lång <[email protected]>2017-03-16 20:49:42 +0100
commitcc115ebc67a465233c7740efb42e0bc9584ad352 (patch)
tree766d1f10b40e4a4c145bad262d2bbd372eb3f636 /lib/hipe/x86/hipe_x86_cfg.erl
parente99f1d41bc8a7e035e35fd5aef6f3ea023d7f12e (diff)
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hipe: Add branch prediction accessor ra callbacks
Adds a new register allocator callback Target:branch_preds(Instr, Context) which, for a control flow instruction Instr, returns a list of tuples {Target, Probability} for each label name Target that Instr may branch to. Probability is a float between 0.0 and 1.0 and corresponds to the predicted probability that control flow branches to the corresponding target. The probabilities may sum to at most 1.0 (rounding errors aside). Note that a sum less than 1.0 is valid.
Diffstat (limited to 'lib/hipe/x86/hipe_x86_cfg.erl')
-rw-r--r--lib/hipe/x86/hipe_x86_cfg.erl22
1 files changed, 21 insertions, 1 deletions
diff --git a/lib/hipe/x86/hipe_x86_cfg.erl b/lib/hipe/x86/hipe_x86_cfg.erl
index a4544e1086..0a3c0fc9d6 100644
--- a/lib/hipe/x86/hipe_x86_cfg.erl
+++ b/lib/hipe/x86/hipe_x86_cfg.erl
@@ -19,7 +19,7 @@
succ/2, pred/2,
bb/2, bb_add/3, map_bbs/2, fold_bbs/3]).
-export([postorder/1, reverse_postorder/1]).
--export([linearise/1, params/1, arity/1, redirect_jmp/3]).
+-export([linearise/1, params/1, arity/1, redirect_jmp/3, branch_preds/1]).
%%% these tell cfg.inc what to define (ugly as hell)
-define(PRED_NEEDED,true).
@@ -72,6 +72,26 @@ branch_successors(Branch) ->
#ret{} -> []
end.
+branch_preds(Branch) ->
+ case Branch of
+ #jmp_switch{labels=Labels} ->
+ Prob = 1.0/length(Labels),
+ [{L, Prob} || L <- Labels];
+ #pseudo_call{contlab=ContLab, sdesc=#x86_sdesc{exnlab=[]}} ->
+ %% A function can still cause an exception, even if we won't catch it
+ [{ContLab, 1.0-hipe_bb_weights:call_exn_pred()}];
+ #pseudo_call{contlab=ContLab, sdesc=#x86_sdesc{exnlab=ExnLab}} ->
+ CallExnPred = hipe_bb_weights:call_exn_pred(),
+ [{ContLab, 1.0-CallExnPred}, {ExnLab, CallExnPred}];
+ #pseudo_jcc{true_label=TrueLab,false_label=FalseLab,pred=Pred} ->
+ [{FalseLab, 1.0-Pred}, {TrueLab, Pred}];
+ _ ->
+ case branch_successors(Branch) of
+ [] -> [];
+ [Single] -> [{Single, 1.0}]
+ end
+ end.
+
-ifdef(REMOVE_TRIVIAL_BBS_NEEDED).
fails_to(_Instr) -> [].
-endif.