beam_bool: Fix generation of code that does not validate

The following code (by Simon Cornish)

bad(XDo1, XDo2, Do3) ->
    Do1    = (XDo1 =/= []),
    Do2    = (XDo2 =/= []),
    CH1 = if Do1 == true;
	     Do1 == false,Do2==false,Do3 == blah ->
		  ch1;
	     true ->
		  no
	  end,
    CH2 = if Do1 == true;
	     Do1 == false,Do2==false,Do3 == xx ->
		  ch2;
	     true ->
		  no
	  end,
    {CH1,CH2}.

is optimized by beam_bool even though the optimization is not
safe. The trouble is that an assignment to {y,0} no longer
occurs on all paths leading to its use.

The bug is in dst_regs/2 which is supposed to return a set
of all registers assigned in a code block, but it ignores
registers assigned in 'move' instructions.

Fix the bug by taking 'move' instructions into account. This change
is safe since it can only cause more registers to be added
to the MustBeKilled and MustBeUnused sets in ensure_opt_safe/6,
which means that it can only cause the optimization to be turned
off for code that used to be optimized.

1 files changed, 30 insertions, 0 deletions

diff --git a/lib/compiler/test/andor_SUITE.erl b/lib/compiler/test/andor_SUITE.erl
index 6e3ac4d4f4..a460d54239 100644
--- a/lib/compiler/test/andor_SUITE.erl
+++ b/lib/compiler/test/andor_SUITE.erl
@@ -390,6 +390,15 @@ before_and_inside_if(Config) when is_list(Config) ->
     ?line yes = before_and_inside_if([], [], x),
     ?line yes = before_and_inside_if([], [b], delete),
     ?line yes = before_and_inside_if([], [b], x),
+
+    ?line {ch1,ch2} = before_and_inside_if_2([a], [b], blah),
+    ?line {ch1,ch2} = before_and_inside_if_2([a], [b], xx),
+    ?line {ch1,ch2} = before_and_inside_if_2([a], [], blah),
+    ?line {ch1,ch2} = before_and_inside_if_2([a], [], xx),
+    ?line {no,no} = before_and_inside_if_2([], [b], blah),
+    ?line {no,no} = before_and_inside_if_2([], [b], xx),
+    ?line {ch1,no} = before_and_inside_if_2([], [], blah),
+    ?line {no,ch2} = before_and_inside_if_2([], [], xx),
     ok.
 
 %% Thanks to Simon Cornish and Kostis Sagonas.
@@ -408,6 +417,27 @@ before_and_inside_if(XDo1, XDo2, Do3) ->
 	    yes
     end.
 
+%% Thanks to Simon Cornish.
+%% Used to generate code that would not set {y,0} on
+%% all paths before its use (and therefore fail
+%% validation by the beam_validator).
+before_and_inside_if_2(XDo1, XDo2, Do3) ->
+    Do1    = (XDo1 =/= []),
+    Do2    = (XDo2 =/= []),
+    CH1 = if Do1 == true;
+	     Do1 == false,Do2==false,Do3 == blah ->
+		  ch1;
+	     true ->
+		  no
+	  end,
+    CH2 = if Do1 == true;
+	     Do1 == false,Do2==false,Do3 == xx ->
+		  ch2;
+	     true ->
+		  no
+	  end,
+    {CH1,CH2}.
+
 %% Utilities.
 
 check(V1, V0) ->