Refactor string operands

There are two instructions that take string operands:

     {bs_put_string,Fail,NumberOfBytes,{string,String}}
     {bs_match_string,Fail,Register,NumberOfBits,{string,String}}

In the canonical BEAM code that is passed to beam_asm, string String
is currently represented as a list. (The string in bs_match_string is
a bitstring before the beam_z compiler pass.) That is wasteful,
because there will be unnecessary conversions between lists and
binaries.

Change the representation of String to be a binary.

Furthermore, bs_put_string is an optimization of a bs_put_binary
instruction with a literal binary operand. Currently, the
bs_put_string instruction is introduced in beam_bs. Delay the
introduction of bs_put_string to the beam_z pass. That will simplify
optimizations and allow us to do the optimization currently done
in beam_bs in a SSA pass in a future commit.

1 files changed, 7 insertions, 8 deletions

diff --git a/lib/compiler/src/beam_dict.erl b/lib/compiler/src/beam_dict.erl
index 990e86062a..b2056332e6 100644
--- a/lib/compiler/src/beam_dict.erl
+++ b/lib/compiler/src/beam_dict.erl
@@ -126,18 +126,17 @@ import(Mod0, Name0, Arity, #asm{imports=Imp0,next_import=NextIndex}=D0)
 	    {NextIndex,D2#asm{imports=Imp,next_import=NextIndex+1}}
     end.
 
-%% Returns the index for a string in the string table (adding the string to the
-%% table if necessary).
+%% Returns the index for a binary string in the string table (adding
+%% the string to the table if necessary).
 %%    string(String, Dict) -> {Offset, Dict'}
--spec string(string(), bdict()) -> {non_neg_integer(), bdict()}.
+-spec string(binary(), bdict()) -> {non_neg_integer(), bdict()}.
 
-string(Str, Dict) when is_list(Str) ->
+string(BinString, Dict) when is_binary(BinString) ->
     #asm{strings=Strings,string_offset=NextOffset} = Dict,
-    StrBin = list_to_binary(Str),
-    case old_string(StrBin, Strings) of
+    case old_string(BinString, Strings) of
 	none ->
-	    NewDict = Dict#asm{strings = <<Strings/binary,StrBin/binary>>,
-			       string_offset=NextOffset+byte_size(StrBin)},
+	    NewDict = Dict#asm{strings = <<Strings/binary,BinString/binary>>,
+			       string_offset=NextOffset+byte_size(BinString)},
 	    {NextOffset,NewDict};
 	Offset when is_integer(Offset) ->
 	    {NextOffset-Offset,Dict}