From 904caa71a3754e3ee7f681cc7d4106d4a9979f1f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Magnus=20L=C3=A5ng?= <margnus1@telia.com>
Date: Wed, 31 Aug 2016 14:48:45 +0200
Subject: hipe: Make sure prepass temps are below SpillLimit

If temps introduced by hipe_regalloc_prepass end up above SpillLimit,
the register allocators will not spill them. This constraint is
unnecessarily limiting the allocators and might theoretically lead to
unallocatable programs (more temps above SpillLimit alive at a time than
there are physical registers).
---
 lib/hipe/regalloc/hipe_regalloc_loop.erl | 59 ++++++++++++++++++++++----------
 1 file changed, 41 insertions(+), 18 deletions(-)

(limited to 'lib/hipe/regalloc/hipe_regalloc_loop.erl')

diff --git a/lib/hipe/regalloc/hipe_regalloc_loop.erl b/lib/hipe/regalloc/hipe_regalloc_loop.erl
index 8d564c35ae..3b21a377df 100644
--- a/lib/hipe/regalloc/hipe_regalloc_loop.erl
+++ b/lib/hipe/regalloc/hipe_regalloc_loop.erl
@@ -34,31 +34,29 @@ ra(CFG, SpillIndex, Options, RegAllocMod, TargetMod) ->
 ra_fp(CFG, Options, RegAllocMod, TargetMod) ->
   ra_common(CFG, 0, Options, RegAllocMod, TargetMod).
 
-ra_common(CFG, SpillIndex, Options, RegAllocMod, TargetMod) ->
+ra_common(CFG0, SpillIndex, Options, RegAllocMod, TargetMod) ->
   ?inc_counter(ra_calls_counter, 1),
+  SpillLimit0 = TargetMod:number_of_temporaries(CFG0),
+  {Coloring, _, CFG, MaybeLiveness} =
+    call_allocator_initial(CFG0, SpillLimit0, SpillIndex, Options, RegAllocMod,
+			   TargetMod),
+  %% The first iteration, the hipe_regalloc_prepass may create new temps, these
+  %% should not end up above SpillLimit.
   SpillLimit = TargetMod:number_of_temporaries(CFG),
-  alloc(CFG, SpillLimit, SpillIndex, Options, RegAllocMod, TargetMod).
+  alloc(Coloring, CFG, MaybeLiveness, SpillLimit, SpillIndex, Options,
+	RegAllocMod, TargetMod).
 
-alloc(CFG0, SpillLimit, SpillIndex, Options, RegAllocMod, TargetMod) ->
+alloc(Coloring, CFG0, MaybeLiveness0, SpillLimit, SpillIndex, Options,
+      RegAllocMod, TargetMod) ->
   ?inc_counter(ra_iteration_counter, 1),
-  {Coloring, _NewSpillIndex, CFG, MaybeLiveness} =
-    case proplists:get_bool(ra_prespill, Options) of
-      true ->
-	hipe_regalloc_prepass:regalloc(
-	  RegAllocMod, CFG0, SpillIndex, SpillLimit, TargetMod, Options);
-      false ->
-	{C, SI, L} = RegAllocMod:regalloc(CFG0, SpillIndex, SpillLimit,
-					  TargetMod, Options),
-	{C, SI, CFG0, L}
-    end,
-  {NewCFG, DidSpill} = TargetMod:check_and_rewrite(CFG, Coloring),
+  {CFG, DidSpill} = TargetMod:check_and_rewrite(CFG0, Coloring),
   case DidSpill of
     false -> %% No new temps, we are done.
       ?add_spills(Options, _NewSpillIndex),
       TempMap = hipe_temp_map:cols2tuple(Coloring, TargetMod),
-      Liveness = liveness_force(TargetMod, CFG, MaybeLiveness),
+      Liveness = liveness_force(TargetMod, CFG0, MaybeLiveness0),
       {TempMap2, NewSpillIndex2} =
-	hipe_spillmin:stackalloc(CFG, Liveness, [], SpillIndex, Options,
+	hipe_spillmin:stackalloc(CFG0, Liveness, [], SpillIndex, Options,
 				 TargetMod, TempMap),
       Coloring2 = 
 	hipe_spillmin:mapmerge(hipe_temp_map:to_substlist(TempMap), TempMap2),
@@ -68,11 +66,36 @@ alloc(CFG0, SpillLimit, SpillIndex, Options, RegAllocMod, TargetMod) ->
       %%   false ->
       %%     ok
       %% end,
-      {NewCFG, Coloring2, NewSpillIndex2};
+      {CFG, Coloring2, NewSpillIndex2};
     _ ->
       %% Since SpillLimit is used as a low-water-mark
       %% the list of temps not to spill is uninteresting.
-      alloc(NewCFG, SpillLimit, SpillIndex, Options, RegAllocMod, TargetMod)
+      {NewColoring, _NewSpillIndex, Liveness} =
+	call_allocator(CFG, SpillLimit, SpillIndex, Options, RegAllocMod,
+		       TargetMod),
+      alloc(NewColoring, CFG, Liveness, SpillLimit, SpillIndex, Options,
+	    RegAllocMod, TargetMod)
+  end.
+
+call_allocator_initial(CFG, SpillLimit, SpillIndex, Options, RegAllocMod,
+		       TargetMod) ->
+  case proplists:get_bool(ra_prespill, Options) of
+    true ->
+      hipe_regalloc_prepass:regalloc_initial(
+	RegAllocMod, CFG, SpillIndex, SpillLimit, TargetMod, Options);
+    false ->
+      {C, SI, L} = RegAllocMod:regalloc(CFG, SpillIndex, SpillLimit,
+					TargetMod, Options),
+      {C, SI, CFG, L}
+  end.
+
+call_allocator(CFG, SpillLimit, SpillIndex, Options, RegAllocMod, TargetMod) ->
+  case proplists:get_bool(ra_prespill, Options) of
+    true ->
+      hipe_regalloc_prepass:regalloc(
+	RegAllocMod, CFG, SpillIndex, SpillLimit, TargetMod, Options);
+    false ->
+      RegAllocMod:regalloc(CFG, SpillIndex, SpillLimit, TargetMod, Options)
   end.
 
 liveness_force(TargetMod, CFG, undefined) -> TargetMod:analyze(CFG);
-- 
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