From cc115ebc67a465233c7740efb42e0bc9584ad352 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Magnus=20L=C3=A5ng?= <margnus1@telia.com>
Date: Sat, 24 Sep 2016 09:37:46 +0200
Subject: 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.
---
 lib/hipe/ppc/hipe_ppc_cfg.erl | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

(limited to 'lib/hipe/ppc')

diff --git a/lib/hipe/ppc/hipe_ppc_cfg.erl b/lib/hipe/ppc/hipe_ppc_cfg.erl
index 58a4d5c8c3..d44d38f38d 100644
--- a/lib/hipe/ppc/hipe_ppc_cfg.erl
+++ b/lib/hipe/ppc/hipe_ppc_cfg.erl
@@ -22,6 +22,7 @@
 -export([postorder/1]).
 -export([linearise/1, params/1, reverse_postorder/1]).
 -export([redirect_jmp/3, arity/1]).
+-export([branch_preds/1]).
 
 %%% these tell cfg.inc what to define (ugly as hell)
 -define(BREADTH_ORDER,true).
@@ -74,6 +75,26 @@ branch_successors(Branch) ->
     #pseudo_tailcall{} -> []
   end.
 
+branch_preds(Branch) ->
+  case Branch of
+    #bctr{labels=Labels} ->
+      Prob = 1.0/length(Labels),
+      [{L, Prob} || L <- Labels];
+    #pseudo_bc{true_label=TrueLab,false_label=FalseLab,pred=Pred} ->
+      [{FalseLab, 1.0-Pred}, {TrueLab, Pred}];
+    #pseudo_call{contlab=ContLab, sdesc=#ppc_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=#ppc_sdesc{exnlab=ExnLab}} ->
+      CallExnPred = hipe_bb_weights:call_exn_pred(),
+      [{ContLab, 1.0-CallExnPred}, {ExnLab, CallExnPred}];
+    _ ->
+      case branch_successors(Branch) of
+	[] -> [];
+	[Single] -> [{Single, 1.0}]
+      end
+  end.
+
 -ifdef(REMOVE_TRIVIAL_BBS_NEEDED).
 fails_to(_Instr) -> [].
 -endif.
-- 
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