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).

1 files changed, 39 insertions, 15 deletions

diff --git a/lib/hipe/regalloc/hipe_regalloc_prepass.erl b/lib/hipe/regalloc/hipe_regalloc_prepass.erl
index 6015c4a042..5a52e5ad51 100644
--- a/lib/hipe/regalloc/hipe_regalloc_prepass.erl
+++ b/lib/hipe/regalloc/hipe_regalloc_prepass.erl
@@ -44,7 +44,7 @@
 %%    hipe_regalloc_loop iteration, skipping directly to rewrite without ever
 %%    calling RegAllocMod.
 -module(hipe_regalloc_prepass).
--export([regalloc/6]).
+-export([regalloc/6, regalloc_initial/6]).
 
 -ifndef(DEBUG).
 -compile(inline).
@@ -137,12 +137,37 @@
 
 -spec regalloc(module(), target_cfg(), spillno(), spillno(), module(),
 	       proplists:proplist())
-	      -> {hipe_map(), spillno(), target_cfg(),
-		  undefined | target_liveness()}.
-regalloc(RegAllocMod, CFG0, SpillIndex0, SpillLimit, Target, Options) ->
+	      -> {hipe_map(), spillno(), target_liveness()}.
+regalloc(RegAllocMod, CFG, SpillIndex0, SpillLimit, Target, Options) ->
+  Liveness = Target:analyze(CFG),
+  {Coloring, SpillIndex, same} =
+    regalloc_1(RegAllocMod, CFG, SpillIndex0, SpillLimit, Target, Options,
+	       Liveness),
+  {Coloring, SpillIndex, Liveness}.
+
+%% regalloc_initial/6 is allowed to introduce new temporaries, unlike regalloc/6
+-spec regalloc_initial(module(), target_cfg(), spillno(), spillno(), module(),
+		       proplists:proplist())
+		      -> {hipe_map(), spillno(), target_cfg(),
+			  undefined | target_liveness()}.
+regalloc_initial(RegAllocMod, CFG0, SpillIndex0, SpillLimit, Target, Options) ->
   Liveness0 = Target:analyze(CFG0),
+  {Coloring, SpillIndex, NewCFG} =
+    regalloc_1(RegAllocMod, CFG0, SpillIndex0, SpillLimit, Target, Options,
+	       Liveness0),
+  %% It's not worth it to add rewriting of the liveness information; just return
+  %% 'undefined' and let it be recomputed when needed.
+  {CFG, Liveness} =
+    case NewCFG of
+      same -> {CFG0, Liveness0};
+      {rewritten, CFG1} -> {CFG1, undefined}
+    end,
+  {Coloring, SpillIndex, CFG, Liveness}.
+
+regalloc_1(RegAllocMod, CFG0, SpillIndex0, SpillLimit, Target, Options,
+	   Liveness) ->
   {ScanBBs, Seen, SpillMap, SpillIndex1} =
-    scan_cfg(CFG0, Liveness0, SpillIndex0, Target),
+    scan_cfg(CFG0, Liveness, SpillIndex0, Target),
 
   AllPrecoloured = Target:all_precoloured(),
 
@@ -157,14 +182,6 @@ regalloc(RegAllocMod, CFG0, SpillIndex0, SpillLimit, Target, Options) ->
 		       CFG0, Target, RegAllocMod, Options)
     end,
 
-  %% It's not worth it to add rewriting of the liveness information; just return
-  %% 'undefined' and let it be recomputed when needed.
-  {CFG, Liveness} =
-    case NewCFG of
-      same -> {CFG0, Liveness0};
-      {rewritten, CFG1} -> {CFG1, undefined}
-    end,
-
   SpillColors = [{T, {spill, S}} || {T, S} <- maps:to_list(SpillMap)],
   Coloring = SpillColors ++ PartColoring,
 
@@ -174,10 +191,17 @@ regalloc(RegAllocMod, CFG0, SpillIndex0, SpillLimit, Target, Options) ->
 			    SpillMap, CFG0, Target),
 	    unused_unused(Unused, CFG0, Target)
 	  end),
-  ?ASSERT(check_coloring(Coloring, CFG, Target)), % Sanity-check
+  ?ASSERT(begin
+	    CFG =
+	      case NewCFG of
+		same -> CFG0;
+		{rewritten, CFG1} -> CFG1
+	      end,
+	    check_coloring(Coloring, CFG, Target)
+	  end), % Sanity-check
   ?ASSERT(just_as_good_as(RegAllocMod, CFG, SpillIndex0, SpillLimit,
 			  Target, Options, SpillMap, Coloring, Unused)),
-  {Coloring, SpillIndex, CFG, Liveness}.
+  {Coloring, SpillIndex, NewCFG}.
 
 regalloc_whole(Seen, SpillMap, SpillIndex0, SpillLimit, ScanBBs,
 	       CFG, Target, RegAllocMod, Options) ->