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.

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.